Logs and metrics for backend services

This document shows you how to configure and use Cloud Logging and Cloud Monitoring with classic Application Load Balancers, global external Application Load Balancers, and Cloud CDN.

Logging

You can enable, disable, and view logs for an external Application Load Balancer backend service. For external Application Load Balancers with backend buckets, logging is automatically enabled and cannot be disabled.

You enable or disable logging for each backend service. You can configure whether to log all requests or a randomly sampled fraction.

You must ensure that you don't have a logs exclusion that applies to external Application Load Balancers. For information about how to verify that Cloud HTTP Load Balancer logs are allowed, see Exclusion filters.

Logs sampling and collection

The requests (and corresponding responses) handled by load balancer backend virtual machine (VM) instances are sampled. These sampled requests are then processed to generate logs. You control the fraction of the requests that are emitted as log entries according to the logConfig.sampleRate parameter. When logConfig.sampleRate is 1.0 (100%), this means that logs are generated for all of the requests and written to Cloud Logging.

Optional fields

Log records contain required fields and optional fields. The What is logged section lists which fields are optional and which are required. All required fields are always included. You can customize which optional fields you keep.

If you select include all optional, all optional fields in the log record format are included in the logs. When new optional fields are added to the record format, the logs automatically include the new fields.
If you select exclude all optional, all optional fields are omitted.
If you select custom, you can specify the optional fields that you want to include, such as tls.protocol,tls.cipher,orca_load_report.cpu_utilization,orca_load_report.mem_utilization.

For information about customizing optional fields, see Enable logging on a new backend service.

Enabling logging on a new backend service

Console

In the Google Cloud console, go to the Load Balancing page.

Go to Load balancing
Click the name of your load balancer.
Click Edit.
Click Backend Configuration.
Select Create a backend service.
Complete the required backend service fields.
In the Logging section, select the Enable logging checkbox.
Set a Sample rate fraction. You can set a number from 0.0 through 1.0, where 0.0 means that no requests are logged and 1.0 means that 100% of the requests are logged. The default value is 1.0.
Optional: To include all the optional fields in the logs, in the Optional fields section, click Include all optional fields.
Pro tip: To specify the CUSTOM option, use the gcloud CLI and the REST API.
To finish editing the backend service, click Update.
To finish editing the load balancer, click Update.

gcloud: Global mode

Create a backend service and enable logging by using the gcloud compute backend-services create command.

gcloud compute backend-services create BACKEND_SERVICE \
    --global \
    --enable-logging \
    --logging-sample-rate=VALUE \
    --load-balancing-scheme=EXTERNAL_MANAGED \
    --logging-optional=LOGGING_OPTIONAL_MODE \
    --logging-optional-fields=OPTIONAL_FIELDS

The gcloud compute backend-services create command supports the following fields:

--global indicates that the backend service is global. Use this field for backend services used with global external Application Load Balancers.
--enable-logging enables logging for that backend service.
--logging-sample-rate lets you specify a value from 0.0 through 1.0, where 0.0 means that no requests are logged and 1.0 means that 100% of the requests are logged. This field is only meaningful with the --enable-logging parameter. Enabling logging but setting the sampling rate to 0.0 is equivalent to disabling logging. The default value is 1.0.
--logging-optional lets you specify the optional fields that you want to include in the logs:
- INCLUDE_ALL_OPTIONAL to include all optional fields.
- EXCLUDE_ALL_OPTIONAL (default) to exclude all optional fields.
- CUSTOM to include a custom list of optional fields that you specify in OPTIONAL_FIELDS.

--logging-optional-fields lets you specify a comma-separated list of optional fields that you want to include in the logs.

For example, tls.protocol,tls.cipher can only be set if LOGGING_OPTIONAL_MODE is set to CUSTOM.

If you use custom metrics and want to log elements of the ORCA load report, you set LOGGING_OPTIONAL_MODE to CUSTOM and specify which elements must be logged in the OPTIONAL_FIELDS field. For example, orca_load_report.cpu_utilization,orca_load_report.mem_utilization.

Enabling logging on an existing backend service

Console

In the Google Cloud console, go to the Load Balancing page.

Go to Load balancing
Click the name of your load balancer.
Click Edit.
Click Backend Configuration.
Click Edit next to your backend service.
In the Logging section, select the Enable logging checkbox.
In the Sample rate field, set the sampling probability. You can set a number from 0.0 through 1.0, where 0.0 means that no requests are logged and 1.0 means that 100% of the requests are logged. The default value is 1.0.
To finish editing the backend service, click Update.
To finish editing the load balancer, click Update.

gcloud: Global mode

Enable logging on an existing backend service with the gcloud compute backend-services update command.

gcloud compute backend-services update BACKEND_SERVICE \
    --global \
    --enable-logging \
    --logging-sample-rate=VALUE \
    --logging-optional=LOGGING_OPTIONAL_MODE \
    --logging-optional-fields=OPTIONAL_FIELDS

where

--global indicates that the backend service is global. Use this field for backend services used with global external Application Load Balancers.
--enable-logging enables logging for that backend service.
--logging-sample-rate lets you specify a value from 0.0 through 1.0, where 0.0 means that no requests are logged and 1.0 means that 100% of the requests are logged. Only meaningful with the --enable-logging parameter. Enabling logging but setting the sampling rate to 0.0 is equivalent to disabling logging. The default value is 1.0.
--logging-optional lets you specify the optional fields that you want to include in the logs.
- INCLUDE_ALL_OPTIONAL to include all optional fields.
- EXCLUDE_ALL_OPTIONAL (default) to exclude all optional fields.
- CUSTOM to include a custom list of optional fields that you specify in OPTIONAL_FIELDS.

--logging-optional-fields lets you specify a comma-separated list of optional fields that you want to include in the logs.

For example, tls.protocol,tls.cipher. Can only be set if LOGGING_OPTIONAL_MODE is set to CUSTOM. If you use custom metrics and want to log elements of the ORCA load report, you set LOGGING_OPTIONAL_MODE to CUSTOM and specify which elements must be logged in the OPTIONAL_FIELDS field. For example, orca_load_report.cpu_utilization,orca_load_report.mem_utilization. * { gcloud: Classic mode }

Enable logging on an existing backend service with the gcloud compute backend-services update command.

<pre class="devsite-click-to-copy">
gcloud compute backend-services update <var>BACKEND_SERVICE</var> \
    --global \
    --enable-logging \
    --logging-sample-rate=<var>VALUE</var>
</pre>

where

* `--global` indicates that the backend service is global. Use this field
  for backend services used with a classic Application Load Balancer.
* `--enable-logging` enables logging for that backend service.
* `--logging-sample-rate` lets you specify a value from
    `0.0` through `1.0`, where `0.0` means that no requests are logged and
    `1.0` means that 100% of the requests are logged. Only meaningful with
    the `--enable-logging` parameter. Enabling logging but setting the
    sampling rate to `0.0` is equivalent to disabling logging. The default
    value is `1.0`.

Disabling or modifying logging on an existing backend service

Console

In the Google Cloud console, go to the Load Balancing page.

Go to Load balancing
Click the name of your load balancer.
Click Edit.
Click Backend Configuration.
Click Edit next to your backend service.
To disable logging entirely, in the Logging section, clear the Enable logging checkbox.
If you leave logging enabled, you can set a different Sample rate fraction. You can set a number from 0.0 through 1.0, where 0.0 means that no requests are logged and 1.0 means that 100% of the requests are logged. The default value is 1.0. For example, 0.2 means 20% of the sampled requests generate logs.
To finish editing the backend service, click Update.
To finish editing the load balancer, click Update.

gcloud: Global mode

Disable logging on a backend service with the gcloud compute backend-services update command.

Disabling logging entirely

gcloud compute backend-services update BACKEND_SERVICE \
    --global \
    --no-enable-logging

where

--global indicates that the backend service is global. Use this field for backend services used with global external Application Load Balancers.
--no-enable-logging disables logging for that backend service.

Enabling logging optional fields on an existing backend service

gcloud compute backend-services update BACKEND_SERVICE \
    --global \
    --enable-logging \
    --logging-sample-rate=VALUE \
    --logging-optional=LOGGING_OPTIONAL_MODE \
    --logging-optional-fields=OPTIONAL_FIELDS

where

--logging-sample-rate lets you specify a value from 0.0 through 1.0, where 0.0 means that no requests are logged and 1.0 means that 100% of the requests are logged. Only meaningful with the --enable-logging parameter. Enabling logging but setting the sampling rate to 0.0 is equivalent to disabling logging. The default value is 1.0.
--logging-optional lets you specify the optional fields that you want to include in the logs:
- INCLUDE_ALL_OPTIONAL to include all optional fields.
- EXCLUDE_ALL_OPTIONAL (default) to exclude all optional fields.
- CUSTOM to include a custom list of optional fields that you specify in OPTIONAL_FIELDS.
--logging-optional-fields lets you specify a comma-separated list of optional fields that you want to include in the logs.

For example, tls.protocol,tls.cipher can only be set if LOGGING_OPTIONAL_MODE is set to CUSTOM. If you use custom metrics and want to log elements of the ORCA load report, you set LOGGING_OPTIONAL_MODE to CUSTOM and specify which elements must be logged in the OPTIONAL_FIELDS field. For example, orca_load_report.cpu_utilization,orca_load_report.mem_utilization.

Updating logging optional mode from CUSTOM to others

gcloud compute backend-services update BACKEND_SERVICE \
    --global \
    --enable-logging \
    --logging-sample-rate=VALUE \
    --logging-optional=LOGGING_OPTIONAL_MODE \
    --logging-optional-fields=

where

--logging-optional lets you specify the optional fields that you want to include in the logs:
- INCLUDE_ALL_OPTIONAL to include all optional fields.
- EXCLUDE_ALL_OPTIONAL (default) to exclude all optional fields.
--logging-optional-fields must be explicitly configured as shown to clear any existing CUSTOM fields. The API doesn't let you combine a non-CUSTOM mode with CUSTOM fields.

Modifying the logging sample rate

gcloud compute backend-services update BACKEND_SERVICE \
    --global \
    --logging-sample-rate=VALUE

gcloud: Classic mode

Disable logging on a backend service with the gcloud compute backend-services update command.

Disabling logging entirely

gcloud compute backend-services update BACKEND_SERVICE \
    --global \
    --no-enable-logging

where

--global indicates that the backend service is global. Use this field for backend services used with a classic Application Load Balancer.
--no-enable-logging disables logging for that backend service.

Modifying the logging sample rate

gcloud compute backend-services update BACKEND_SERVICE \
    --global \
    --logging-sample-rate=VALUE

where

--global indicates that the backend service is global. Use this field for backend services used with a classic Application Load Balancer.
--logging-sample-rate lets you specify a value from 0.0 through 1.0, where 0.0 means that no requests are logged and 1.0 means that 100% of the requests are logged. Only meaningful with the --enable-logging parameter. Enabling logging but setting the sampling rate to 0.0 is equivalent to disabling logging.

View logs

To follow step-by-step guidance for this task directly in the Google Cloud console, click Guide me:

Guide me

HTTP(S) logs are indexed first by a forwarding rule, then by a URL map.

To view logs, go to the Logs Explorer page:

Go to Logs Explorer

To view all logs, in the Resource filter menu, select Cloud HTTP Load Balancer > All forwarding rules.
To view logs for one forwarding rule, select a single forwarding rule name.
To view logs for one URL map, select a forwarding rule, and then select a URL map.

Log fields of type boolean typically only appear if they have a value of true. If a boolean field has a value of false, that field is omitted from the log.

UTF-8 encoding is enforced for log fields. Characters that are not UTF-8 characters are replaced with question marks. For classic Application Load Balancers and global external Application Load Balancers, you can export logs-based metrics using resource logs (resource.type="http_load_balancer"). The metrics created are based on the Application Load Balancer Rule (Logs-based Metrics) resource (l7_lb_rule), which is available under Cloud Monitoring dashboards instead of under the https_lb_rule resource.

What is logged

External Application Load Balancer log entries contain information useful for monitoring and debugging your HTTP(S) traffic. Log records contain required fields, which are the default fields of every log record.

Log records contain optional fields that add additional information about your HTTP(S) traffic. Optional fields can be omitted to save storage costs.

Some log fields are in a multi-field format, with more than one piece of data in a given field. For example, the tls field is of the TlsInfo format, which contains the earlyDataRequest field. These multi-field fields are described in the following record format table.

Field	Field format	Field type: Required or Optional	Description
Field	Field format	Field type: Required or Optional	Description	severity insertID logName	LogEntry	Required	The general fields as described in a log entry.
timestamp	string (Timestamp format)	Optional	The time when the first layer GFE receives the request.
httpRequest	HttpRequest	Required	A common protocol for logging HTTP requests. `HttpRequest.protocol` isn't populated for `resource.type="http_load_balancer"` .
resource	MonitoredResource	Required	The MonitoredResource is the resource type associated with a log entry. The MonitoredResourceDescriptor describes the schema of a `MonitoredResource` object by using a type name and a set of labels. For more information, see Resource labels.
jsonPayload	object (Struct format)	Required	The log entry payload that is expressed as a JSON object. The JSON object contains the following fields: `statusDetails` `backendTargetProjectNumber` `overrideResponseCode` `errorService` `errorBackendStatusDetails` `authzPolicyInfo` `loadBalancingScheme` `tls` `orca_load_report`
	string	Required	The `statusDetails` field holds a string that explains why the load balancer returned the HTTP status code that it did. For more information about these log strings, see statusDetails HTTP success messages and statusDetails HTTP failure messages.
	string	Required	The `backendTargetProjectNumber` field holds the project number where the backend target—backend service or backend bucket—has been created. This field is in the format: `"projects/PROJECT_NUMBER"`. This information is only available for global external Application Load Balancers using custom error responses.
	integer	Required	The `overrideResponseCode` holds the override response code applied to the response sent to the client. This information is only available for global external Application Load Balancers using custom error responses.
	string	Required	The `errorService` field holds the backend service that provided the custom error response. This information is only available for global external Application Load Balancers using custom error responses.
	string	Required	The `errorBackendStatusDetails` field holds the `statusDetails` of the final response served to the client. This information is only available for global external Application Load Balancers using custom error responses.
	AuthzPolicyInfo	Required	The `authzPolicyInfo` field stores information about the authorization policy result. This information is only available for global external Application Load Balancers that have enabled authorization policies. For more information, see what is logged for authorization policies.
	string	Optional	The `loadBalancingScheme` field is only populated if you use the classic Application Load Balancer migration feature. This field holds a string that describes which load balancing scheme was used to route the request. The possible values are either `EXTERNAL` or `EXTERNAL_MANAGED`.
	TlsInfo	Required	The `tls` field holds the TlsInfo field that specifies the TLS metadata for the connection between the client and the load balancer. This field is only available if the client is using TLS/SSL encryption. Use the `--logging-optional-fields` parameter to specify which elements must be logged: Optional: `tls.protocol` Optional: `tls.cipher` Required: `tls.earlyDataRequest` You can't set `--logging-optional-fields` to `tls` to specify all elements.
	OrcaLoadReport	Optional	The `orca_load_report` field contains some or all elements of the ORCA load report returned by the backend. This field is only present if the backend returns an ORCA load report and you configured the load balancer to log the ORCA load report. Use the `--logging-optional-fields` parameter to specify which of the following elements of the ORCA load report must be logged: `orca_load_report.cpu_utilization` `orca_load_report.mem_utilization` `orca_load_report.request_cost` `orca_load_report.utilization` `orca_load_report.rps_fractional` `orca_load_report.eps` `orca_load_report.named_metrics` `orca_load_report.application_utilization` You can also set `--logging-optional-fields` to `orca_load_report` to specify that all elements must be logged.

Note: Redirects (HTTP response status code 302 Found) that are issued from the load balancer are not logged. Redirects issued from the backend instances are logged.

TlsInfo field format

Field	Field format	Field type: Required or Optional	Description
protocol	string	Optional	TLS protocol that clients use to establish a connection with the load balancer. Possible values are `TLSv1`, `TLSv1.1`, `TLSv1.2`, `TLSv1.3`, or `QUIC`. This value is set to `NULL` if the client is not using TLS/SSL encryption.
cipher	string	Optional	TLS cipher that clients use to establish a connection with the load balancer. This value is set to `NULL` if the client isn't using HTTP(S) or the client isn't using TLS/SSL encryption.
earlyDataRequest	boolean	Required	The request includes early data in the TLS handshake.

Resource labels

The following table lists the resource labels for resource.type="http_load_balancer".

Field	Type	Description
`backend_service_name`	string	The name of the backend service.
`forwarding_rule_name`	string	The name of the forwarding rule object.
`project_id`	string	The identifier of the Google Cloud project associated with this resource.
`target_proxy_name`	string	The name of the target proxy object referenced by the forwarding rule.
`url_map_name`	string	The name of the URL map object configured to select a backend service.
`zone`	string	The zone in which the load balancer is running. The zone is `global`.

statusDetails HTTP success messages

statusDetails (successful)	Meaning	Common accompanying response codes
`byte_range_caching`	The HTTP request was served using Cloud CDN byte range caching.	Any cacheable response code is possible.
`response_from_cache`	The HTTP request was served from a Cloud CDN cache.	Any cacheable response code is possible.
`response_from_cache_validated`	The return code was set from a Cloud CDN cached entry that was validated by a backend.	Any cacheable response code is possible.
`response_sent_by_backend`	The HTTP request was proxied successfully to the backend, and the response was returned by the backend.	The HTTP response code is set by the software running on the backend.

statusDetails HTTP failure messages

Filter this table:

statusDetails (failure)	Meaning	Common accompanying status codes
`aborted_request_due_to_backend_early_response`	A request with body was aborted due to the backend sending an early response with a status code. The response was forwarded to the client. The request was terminated.	`4XX` or `5XX`
`backend_connection_closed_after_partial_response_sent`	The backend connection closed unexpectedly after a partial response had been sent to the client.	The HTTP status code is set by the software running on the backend. HTTP status code `0` (zero) means that the backend sent incomplete HTTP headers. The HTTP status code is `101` if the HTTP(S) connection was upgraded to a websocket connection.
`backend_connection_closed_before_data_sent_to_client`	The backend unexpectedly closed its connection to the load balancer before the response was proxied to the client.	502, 503 The HTTP status code is `101` if the HTTP(S) connection was upgraded to a websocket connection.
`backend_early_response_with_non_error_status`	The backend sent a non-error status code (`1XX` or `2XX`) to a request before receiving the whole request body.	`502`, `503`
`backend_interim_response_not_supported`	The backend sent an interim `1XX` status code to the request in a context where interim responses aren't supported.	`502`, `503`
`backend_response_corrupted`	The HTTP response body sent by the backend has invalid chunked transfer-encoding or is otherwise corrupted.	Any status code possible depending on the nature of the corruption. Often `502`, `503`.
`backend_response_headers_too_long`	The HTTP response headers sent by the backend exceeded the allowed limit. See the Header size for external Application Load Balancers section for more information.	`502`, `503`
`backend_timeout`	The backend timed out while generating a response. For a websocket connection: For global external Application Load Balancer, a status code is generated when the GFE closes the websocket connection in idle state after the backend service timeout expires. For classic Application Load Balancer, a status code is generated when the GFE closes the websocket connection in either idle or active state, after the backend service timeout expires.	`502`, `503` The HTTP status code is `101` if the HTTP(S) connection was upgraded to a websocket connection.
`banned_by_security_policy`	The request was banned by a Cloud Armor rate-based ban rule.	`429`
`body_not_allowed`	The client sent an HTTP request with a body, but the HTTP method used doesn't allow a body.	`400`
`byte_range_caching_aborted`	The load balancer previously received a response indicating that the resource was cacheable and supported byte ranges. Cloud CDN received an inconsistent response (for example, one with a status code other than the expected `206 Partial Content`). This happened when attempting to perform cache fill using a byte range request. As a result, the load balancer aborted the response to the client.	`2XX`
`byte_range_caching_forwarded_backend_response`	The load balancer previously received a response indicating that the resource was cacheable and supported byte ranges. Cloud CDN received an inconsistent response (for example, one with a status code other than the expected `206 Partial Content`). This happened when attempting to perform cache fill using a byte range request. The load balancer then forwarded the inconsistent response to the client.	Returned from the backend—any status code is possible.
`byte_range_caching_retrieval_abandoned`	The client canceled a byte range request or validation request initiated by Cloud CDN.	Returned from the backend—any status code is possible.
`byte_range_caching_retrieval_from_backend_failed_after_partial_response`	A byte range request or validation request initiated by Cloud CDN encountered an error. Refer to the corresponding Cloud Logging log entry for the request initiated by Cloud CDN for the detailed backend status.	`2XX`
`cache_lookup_failed_after_partial_response`	The load balancer failed to serve a full response from Cloud CDN cache due to an internal error.	`2XX`
`cache_lookup_timeout_after_partial_response`	The Cloud CDN cache lookup stream timed out because the client didn't retrieve the content in a timely manner.	`2XX`
`client_disconnected_after_partial_response`	The connection to the client was broken after the load balancer sent a partial response.	Returned from the backend—any status code is possible. The HTTP status code is `101` if the HTTP(S) connection was upgraded to a websocket connection.
`client_disconnected_before_any_response`	The connection to the client was broken before the load balancer sent any response.	`0` The HTTP status code is `101` if the HTTP(S) connection was upgraded to a websocket connection.
`client_timed_out`	The Google Front End (GFE) idled out the client connection due to lack of progress while it was proxying either the request or the response.	`0` or `408`
`client_cert_invalid_rsa_key_size`	A client leaf or intermediate certificate had an invalid RSA key size. For more information, see Logged errors for closed connections.	`0`
`client_cert_unsupported_elliptic_curve_key`	A client or intermediate certificate is using an unsupported elliptic curve. For more information, see Logged errors for closed connections.	`0`
`client_cert_unsupported_key_algorithm`	A client or intermediate certificate is using a non-RSA or non-ECDSA algorithm. For more information, see Logged errors for closed connections.	`0`
`client_cert_pki_too_large`	The PKI to be used for validation has more than ten intermediate certificates that share the same Subject and Subject Public Key Info. For more information, see Logged errors for closed connections.	`0`
`client_cert_chain_max_name_constraints_exceeded`	An intermediate certificate provided for validation had more than ten name constraints. For more information, see Logged errors for closed connections.	`0`
`client_cert_chain_invalid_eku`	Either the client certificate or its issuer doesn't have Extended Key Usage (EKU) that includes `clientAuth`. For more information, see Logged errors for closed connections.	`0`
`client_cert_validation_timed_out`	Time limit exceeded while validating the certificate chain. For more information, see Logged errors for closed connections.	`0`
`client_cert_validation_search_limit_exceeded`	The depth or iteration limit is reached while attempting to validate the certificate chain. For more information, see Logged errors for closed connections.	`0`
`client_cert_validation_not_performed`	You have configured mTLS without setting up a `TrustConfig`. For more information, see Logged errors for closed connections.	`0`
`client_cert_not_provided`	The client didn't provide the requested certificate during the handshake. For more information, see Logged errors for closed connections.	`0`
`client_cert_validation_failed`	Client certificate fails validation with the `TrustConfig` when hashing algorithms such as MD4, MD5, and SHA-1 are used. For more information, see Logged errors for closed connections.	`0`
`config_not_found`	The load balancer is missing project configuration. This can occur intermittently after you've made configuration changes that add a new resource. Another cause of the error is that the first-layer GFE fails to communicate with the second-layer GFE. This can be due to an internal error, such as an in-progress rollout, load balancer overload, or intermittent configuration issues. These errors are transient in nature and are expected to fall well within the SLA. However, if the error rate exceeds 0.01%, please contact Google Cloud support for further assistance.	`404`, `502`, `503`
`direct_response`	The load balancer overrode this request and returned a fixed response.	You might see any HTTP status code depending on the nature of the issue. For example, the HTTP `410` status code means that the backend is unavailable due to payment delinquency.
`denied_by_security_policy`	The load balancer denied this request because of a Google Cloud Armor security policy.	Configured in the security policy.
`error_uncompressing_gzipped_body`	There was an error uncompressing a gzipped HTTP response.	`502`, `503`
`failed_to_connect_to_backend`	The load balancer failed to connect to the backend. This includes timeouts during the connection phase.	`502`, `503`
`failed_to_pick_backend`	The load balancer failed to pick a healthy backend to handle the request.	`502`, `503`
`failed_to_negotiate_alpn`	The load balancer and the backend failed to negotiate an application layer protocol (such as HTTP/2) to use to communicate with each other over TLS.	`502`, `503`
`headers_too_long`	The request headers were larger than the maximum allowed.	`413`
`http_version_not_supported`	HTTP version not supported. Only HTTP 0.9, 1.0, 1.1, and 2.0 are supported.	`400`
`internal_error`	Internal error at the load balancer. Normally represents a transient error in the load balancer infrastructure. Retry your query.	`4XX` or `5XX`
`invalid_chunk_framing`	Requests and responses sent with the `Transfer-Encoding: Chunked` header are not RFC 9112 compliant. As per the RFC, both the `chunked_body` and the `last-chunk` fields must end in `CRLF`.	`400`
`invalid_external_origin_endpoint`	The configuration for the external backend is invalid. Review the internet NEG configuration and ensure that it specifies a valid FQDN/IP address and port.	`4XX`
`invalid_request_headers`	The HTTP request headers received from a client contain at least one character that isn't allowed under an applicable HTTP specification. For example, header field names that include a double quotation mark (`"`) or any characters outside of the standard ASCII range (that is, any byte >= `0x80`) are invalid. For more information, see: The "5.5. Field Values" section of RFC 9110 The "5. Field Syntax" section of RFC 9112 The "8.2.1. Field Validity" section of RFC 9113	`400`
`invalid_http2_client_header_format`	The HTTP/2 headers from a client are invalid. For more information, see `invalid_request_headers`.	`400`
`invalid_http2_client_request_path`	The HTTP/2 request path from a client contains at least one character that isn't allowed under the URI specification. For more information, see the "3.3. Path" section of RFC 3986.	`400`
`multiple_iap_policies`	Multiple Identity-Aware Proxy (IAP) policies cannot be combined. If you have an IAP policy attached to a backend service and another policy attached to a serverless object, remove one of the policies and try again. Serverless objects include App Engine, Cloud Run, and Cloud Run functions.	`500`
`malformed_chunked_body`	The request body was improperly chunk encoded.	`411`
`request_loop_detected`	The load balancer detected a request loop. This loop might be caused by a misconfiguration where the backend forwarded the request back to the load balancer.	`502`, `503`
`required_body_but_no_content_length`	The HTTP request requires a body but the request headers don't include a content length or transfer-encoding chunked header.	`400`, `403`, `411`
`retriable_error`	The load balancer has encountered an infrastructure error and the request can be retried. This can occur intermittently after you've made configuration changes that add or reference a new resource. This can also occur when the first-layer GFE fails to communicate with the second-layer GFE due to an internal error, such as an in-progress rollout, load balancer overload, or intermittent configuration issue. These errors are transient in nature and are expected to fall well within the SLA. However, if the error rate exceeds 0.01% over a sustained period, please contact Google Cloud support for further assistance.	`404`, `502`, `503`
`secure_url_rejected`	A request with an `https://` URL was received over a plaintext HTTP/1.1 connection.	`400`
`server_cert_chain_exceeded_limit`	The server certificate chain is too long (more than 10 intermediate certificates included with the server certificate).	`502`, `503`
`server_cert_chain_invalid_eku`	The server certificate has an `Extended Key Usage (EKU)` extension field but that field doesn't include `serverAuth`.
`server_cert_chain_max_name_constraints_exceeded`	An intermediate certificate provided for validation had more than 10 name constraints.	`502`, `503`
`server_cert_exceeded_size_limit`	The server certificate payload (including any intermediate certificates) is too large (more than 16 KB).	`503`
`server_cert_invalid_rsa_key_size`	A server or an intermediate certificate has an invalid RSA key size. No validation is performed. RSA keys can range from 2048 to 4096 bits.	`503`
`server_cert_not_provided`	The server did not provide the requested certificate during the handshake.	`503`
`server_cert_pki_too_large`	The PKI to be used for validation has more than ten intermediate certificates that share the same Subject and Subject Public Key Info. No validation is performed.	`503`
`server_cert_trust_config_not_found`	Matching `TrustConfig` not found.	`503`
`server_cert_unsupported_elliptic_curve_key`	A server or an intermediate certificate is using an unsupported elliptic curve. No validation is performed. Valid curves are P-256 and P-384.	`503`
`server_cert_unsupported_key_algorithm`	A server or an intermediate certificate is using a non-RSA or non-ECDSA algorithm. No validation is performed.	`503`
`server_cert_validation_internal_error`	Internal error validating certificate chain.	`503`
`server_cert_validation_not_performed`	You configured mTLS without setting up a `TrustConfig` resource.	`503`
`server_cert_validation_search_limit_exceeded`	The depth or iteration limit is reached while attempting to validate the certificate chain. The maximum depth for a certificate chain is ten, including the root and server certificates. The maximum number of iterations is 100 (certificates examined to validate the server certificate chain).	`503`
`server_cert_validation_timed_out`	The time limit is exceeded while attempting to validate the certificate chain.	`503`
`server_cert_validation_unavailable`	Service is unable to perform certificate chain validation.	`503`
`ssl_certificate_san_verification_failed`	The load balancer cannot find a Subject Alternative Name (SAN) in the SSL certificate presented by the backend that matches the configured hostname.	`502`, `503`
`ssl_certificate_chain_verification_failed`	The SSL certificate presented by the backend failed SSL certificate verification.	`502`, `503`
`throttled_by_security_policy`	The request was blocked by a Cloud Armor throttle rule.	`429`
`unsupported_method`	The client supplied an unsupported HTTP request method.	`400`
`unsupported_100_continue`	The client request included the 'Expect: 100-continue' header on a protocol that doesn't support it.	`400`
`upgrade_header_rejected`	The client HTTP request contained the Upgrade header and was refused.	`400`
`websocket_closed`	The websocket connection was closed.	`101`
`websocket_handshake_failed`	The websocket handshake failed.	Any status code possible depending on the nature of the handshake failure.
`request_body_too_large`	The HTTP request body exceeded the maximum supported by the backend. Not applicable for VM backends.	`413`
`handled_by_identity_aware_proxy`	This response was generated by Identity-Aware Proxy during identity verification of the client before allowing access.	`200`, `302`, `400`, `401`, `403`, `500`, `502`, `503` `429` (throttled by IAP)
`serverless_neg_routing_failed`	The serverless NEG request cannot be dispatched. This error can happen when the region specified in the NEG cannot be reached, or when the resource name (for example, the Cloud Run functions name) cannot be found.	`404`, `502`, `503`
`fault_filter_abort`	This error can happen if the customer has configured a fault filter and the fault filter was triggered for the given request.	The value must be from `200` to `599`.
`early_data_rejected`	The request sent in TLS early data was invalid. This might occur in the following cases but isn't limited to them: The `TargetHttpsProxy` has TLS early data set to `STRICT`, but the request included query parameters. The `TargetHttpsProxy` has TLS early data set to `STRICT` or `PERMISSIVE`, but the request used a nonidempotent HTTP method (such as POST or PUT).	425
`service_extension_error`	There was an error calling out to a service extension used by the load balancer. This might occur if the Wasm plugin is slow to respond and exceeds the 1 millisecond limit to send its response.	425

View logs for mTLS client certificate validation

To view the logged errors for closed connections during mutual TLS client certificate validation, complete the following steps.

Console query

In the Google Cloud console, go to the Logs Explorer page.

Go to Logs Explorer
Click the Show query toggle.

Paste the following into the query field. Replace FORWARDING_RULE_NAME with the name of your forwarding rule.

jsonPayload.statusDetails=~"client_cert"
jsonPayload.@type="type.googleapis.com/google.cloud.loadbalancing.type.LoadBalancerLogEntry"
resource.labels.forwarding_rule_name=FORWARDING_RULE_NAME

Click Run query.

Authorization policy request logs

The authz_info object in the Load Balancer Log Entry JSON payload contains information about authorization policies. You can configure log-based metrics for traffic allowed or denied by these policies. Check more authorization policies log details.

Field	Type	Description
`authz_info.policies[]`	object	The list of policies that match the request.
`authz_info.policies[].name`	string	The name of the authorization policy that matches the request. The name is empty for the following reasons: No `ALLOW` policy matches the request and the request is denied. No `DENY` policy matches the request and the request is allowed.
`authz_info.policies[].result`	enum	The result can be `ALLOWED` or `DENIED`.
`authz_info.policies[].details`	string	The details include the following: `allowed_as_no_deny_policies_matched_request` `denied_as_no_allow_policies_matched_request` `denied_by_authz_extension` `denied_by_cloud_iap`
`authz_info.overall_result`	enum	The result can be `ALLOWED` or `DENIED`.

Logging for Cloud Armor

The table for statusDetail HTTP failure messages contains some messages that apply to Cloud Armor. For more information about what Cloud Armor logs, see Use request logging.

Logging for Shared VPC deployments

Application Load Balancer logs and metrics are typically exported to the project that has the forwarding rule. Therefore, service admins—owners or users of projects where the backend service is created—won't have access to the load balancer's logs and metrics by default. You can use IAM roles to grant these permissions to service admins. To learn more about the IAM roles that are available, and the steps to provide access, see Grant access to Monitoring.

Interacting with the logs

You can interact with the external Application Load Balancer logs by using the Cloud Logging API. The Logging API provides ways to interactively filter logs that have specific fields set. It exports matching logs to Cloud Logging, Cloud Storage, BigQuery, or Pub/Sub. For more information about the Logging API, see Logging API overview.

Monitoring

The load balancer exports monitoring data to Monitoring.

You can use monitoring metrics to do the following:

Evaluate a load balancer's configuration, usage, and performance
Troubleshoot problems
Improve resource utilization and user experience

Metric reporting frequency and retention

Metrics for the external Application Load Balancers are exported to Cloud Monitoring in 1-minute granularity batches. Monitoring data is retained for six (6) weeks.

The dashboard provides data analysis in default intervals of 1H (one hour), 6H (six hours), 1D (one day), 1W (one week), and 6W (six weeks). You can manually request analysis in any interval from 6W to 1 minute.

Monitoring metrics

You can monitor the following metrics for external Application Load Balancers.

The following metrics for global external Application Load Balancers are reported into Cloud Monitoring. These metrics are prepended with loadbalancing.googleapis.com/.

Filter this table:

Metric	Name	Description
Request count	`https/request_count`	The number of requests served by the external Application Load Balancer
Request bytes count	`https/request_bytes_count`	The number of bytes sent as requests from clients to the external Application Load Balancer
Response bytes count	`https/response_bytes_count`	The number of bytes sent as responses from the external Application Load Balancer to clients
Total latencies	`https/total_latencies`	A distribution of the total latency. Total latency is the time in milliseconds between the first byte of the request received by the proxy and the last byte of the response sent by the proxy. It includes: the time taken by the proxy to process the request, the time taken for the request to be sent from the proxy to the backend, the time taken by the backend to process the request, the time taken for the response to be sent back to the proxy, and the time taken for the proxy to process the response and send the response to the client. It doesn't include the RTT between the client and the proxy. Additionally, pauses between requests on the same connection that use `Connection: keep-alive` do not affect the measurement. This measurement is typically reduced to the 95th percentile in Cloud Monitoring views. For websocket connections, this field refers to the entire time duration of the connection.^* Example: A load balancer has 1 request per second from the UK, all with 100 ms latency, and 9 requests per second from the US, all with 50 ms latency. Over a certain minute there were 60 requests from the UK and 540 requests from the US. Monitoring metrics preserves the distribution over all dimensions. You can request information such as the following: median overall latency (300/600) - 50 ms median UK latency (30/60) - 100 ms 95th percentile overall latency (570/600) - 100 ms
Frontend RTT^†	`https/frontend_tcp_rtt`	A distribution of the frontend RTT. Frontend RTT is the time in milliseconds it takes for data to travel from the client to the proxy and back again. It includes the time taken for a request to travel from the client to the proxy and back from the proxy to the client. This is not updated during the lifetime of the connection. For example, setting up a (TCP) connection with a 3-way handshake would take 1.5 RTTs. When requests are processed, the load balancer samples and averages the time it takes for data to travel back and forth between the client and the proxy, and then logs a smoothed RTT value. Smoothed RTT is an algorithm that deals with variations and anomalies that might occur in RTT measurements.
Backend latencies^†	`https/backend_latencies`	A distribution of the backend latency. Backend latency is the time in milliseconds between the first byte of the request received by the backend and the last byte of the response received by the proxy. It includes: the time taken for the request to be sent from the proxy to the backend, the time taken by the backend to process the request, and the time taken for the response to be sent back to the proxy.
Response code class fraction		Fraction of total external Application Load Balancer responses that are in each response code class (`2xx`, `4xx`, ...). In Monitoring, this value is only available on default dashboards. It isn't available for custom dashboards. You can use the Monitoring API to set alerts for it.
Backend request count	`https/backend_request_count`	The number of requests sent from the external Application Load Balancer to the backends.
Backend request bytes count	`https/backend_request_bytes_count`	The number of bytes sent as requests from the external Application Load Balancer to the backends.
Backend response bytes count	`https/backend_response_bytes_count`	The number of bytes sent as responses from the backends (including cache) to the external Application Load Balancer.

^* For monitoring websocket connections, create a backend service specifically for websockets.

^† The sum of Frontend RTT and Backend latencies might not be less than or equal to Total latencies. This is because although we poll RTT over the socket from the GFE to the client at the time the HTTP response is acknowledged, we rely on kernel reporting for some of these measurements, and we cannot be sure that the kernel will have an RTT measurement for the given HTTP response. The end result is a smoothed RTT value that is also affected by previous HTTP responses, SYN/ACKs, and SSL handshakes that aren't affecting current HTTP request actual timings.

Filtering dimensions for metrics

You can apply filters for metrics for external Application Load Balancers.

Metrics are aggregated for each classic Application Load Balancer and global external Application Load Balancer. You can filter aggregated metrics by the following dimensions for resource.type="http_load_balancer" or resource.type="https_lb_rule". Note that not all dimensions are available on all metrics.

Filter this table:

Property	Description
`backend_scope`	The Google Cloud scope (region or zone) of the backend service instance group that served the connection. If no instance group was available or if the request was served by another entity, you see one of the following values instead of the region or zone of the backend service instance group. `FRONTEND_5xx`: an internal error occurred before the GFE could select a backend. The GFE returned `5xx` to the client. INVALID_BACKEND: the GFE couldn't find a healthy backend to assign the request to, so it returned a `5xx` status code to the requestor. NO_BACKEND_SELECTED: either an error or interruption occurred before a backend was selected, a URL redirect occurred, or a classic Application Load Balancer with serverless backends returned a `200 OK` response. MULTIPLE_BACKENDS: the request was served by potentially multiple backends. This can happen when Cloud CDN has served the request partially from its cache and has also sent one or more byte range requests to the backend. Use the `backend_scope` breakdown to visualize each load balancer-to-backend request. When this breakdown is chosen, the charts show backend metrics (load balancer-to-backends), not frontend metrics (client-to-load balancer).
`backend_type`	The name of the backend group that served the client's request. Can be `INSTANCE GROUP`, `NETWORK_ENDPOINT_GROUP`, or `UNKNOWN` is returned if the backend wasn't assigned. If no backend group was available or if the request was served by another entity, one of the following values is displayed instead of a backend group. FRONTEND_5XX: an internal error occurred before the GFE could select a backend. The GFE returned `5xx` to the client. INVALID_BACKEND: the GFE couldn't find a healthy backend to assign the request to, so it returned a `5xx` status code to the requestor. NO_BACKEND_SELECTED: either an error or interruption occurred before a backend was selected, a URL redirect occurred, or a classic Application Load Balancer with serverless backends returned a `200 OK` response. MULTIPLE_BACKENDS: the request was served by potentially multiple backends. This can happen when Cloud CDN has served the request partially from its cache and has also sent one or more byte range requests to the backend. Use the `backend_scope` breakdown to visualize each load balancer-to-backend request.
`backend_target_type`	The name of the backend service that served the request. Can be `BACKEND_SERVICE`, `BACKEND_BUCKET`, `UNKNOWN` if the backend wasn't assigned, or `NO_BACKEND_SELECTED` if an error or interruption occurred before a backend was selected, a URL redirect occurred, or a classic Application Load Balancer with serverless backends returned a `200 OK` response.
`matched_url_path_rule`	The URL map path rule that matched the prefix of the HTTP(S) request (up to 50 characters).
`forwarding_rule_name`	The name of the forwarding rule used by the client to send the request.
`url_map_name`	The URL map path rule or route rule configured as part of the URL map key. Can be `UNMATCHED` or `UNKNOWN` as fallbacks. `UNMATCHED` refers to a request that doesn't match any URL path rules, so `url_map_name` uses the default path rule. `UNKNOWN` indicates an internal error.
`target_proxy_name`	The name of the target HTTP(S) proxy object referenced by the forwarding rule.
`backend_target_name`	The name of the backend target. The target can be either a backend service or backend bucket. `UNKNOWN` is returned if a backend wasn't assigned.
`backend_name`	The name of the backend instance group, bucket, or NEG. `UNKNOWN` is returned if the backend wasn't assigned, or `NO_BACKEND_SELECTED` if an error or interruption occurred before a backend was selected, a URL redirect occurred, or a classic Application Load Balancer with serverless backends returned a `200 OK` response.
`backend_scope_type`	The type of the scope of the backend group. Can be `GLOBAL`, `REGION`, `ZONE`, `MULTIPLE_BACKENDS`, or `NO_BACKEND_SELECTED` if an error or interruption occurred before a backend was selected, a URL redirect occurred, or a classic Application Load Balancer with serverless backends returned a `200 OK` response, or other possible backend_type outputs. `MULTIPLE_BACKENDS` is used when chunk caching is used. Multiple queries are sent to the same backend for different chunks of data to support a single client request.
`proxy_continent`	Continent of the HTTP(S) GFE that terminated the HTTP(S) connection—for example, `America`, `Europe`, `Asia`
`protocol`	Protocol used by the client, one of `HTTP/1.0`, `HTTP/1.1`, `HTTP/2.0`, `QUIC/HTTP/2.0`, `UNKNOWN`.
`response_code`	The HTTP status code of the request.
`response_code_class`	The HTTP status code class of the request: `200`, `300`, `400`, `500` or `0` for none.
`cache_result`	Cache result for serving HTTP request by proxy: `HIT`, `MISS`, `DISABLED`, `PARTIAL_HIT` (for a request served partially from cache and partially from backend), or `UNKNOWN`.
`client_country`	Country of the client that issued the HTTP request—for example, `United States` or `Germany`.
`load_balancing_scheme`	The load balancing scheme used. If classic Application Load Balancer is used, the value is `EXTERNAL`. If global external Application Load Balancer is used, the value is `EXTERNAL_MANAGED`.

What's next

Read the overview of Cloud CDN logging
Read about caching.
Read about signed URLs and signed cookies.