Regional external Application Load Balancer logging and monitoring

This document shows you how to configure and use Cloud Logging and Cloud Monitoring with regional external Application Load Balancers.

Logging

You can enable, disable, and view logs for an external Application Load Balancer backend service.

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 instructions about how to verify that Cloud HTTP Load Balancer logs are allowed, see Viewing resource-type exclusions.

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.

For instructions 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: Regional mode

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

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

where

--region indicates that the backend service is regional. Use this field for backend services used with regional 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.

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.
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: Regional mode

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

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

where

--region indicates that the backend service is regional. Use this field for backend services used with regional 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.

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: Regional 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 \
    --region=REGION \
    --no-enable-logging

where

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

Modifying the logging sample rate

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

View logs

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 regional external Application Load Balancers, you can export logs-based metrics using resource logs (resource.type="http_external_regional_lb_rule").

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 TlsDetails format, which contains the TLS protocol and TLS cipher in a single 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 timestamp logName	LogEntry	Required	The general fields as described in a log entry.
httpRequest	HttpRequest	Required	A common protocol for logging HTTP requests.
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: `proxyStatus` `tls` `backendTargetProjectNumber` `mtls`
	string	Required	The `proxyStatus` field holds a string that specifies why the regional external Application Load Balancer returned the `HttpRequest.status`. The field is not logged if the value is an empty string. This can happen if the proxy or backend doesn't return an error or the error code that is not `0`, `4XX`, or `5XX`. The `proxyStatus` field has two parts: proxyStatus error Optional: proxyStatus details
	TlsDetails	Optional	The `tls` field holds the TlsDetails that specifies the TLS metadata for the connection between the client and the regional external Application Load Balancer. This field is only available if the client is using TLS/SSL encryption.
	MtlsDetails	Optional	The `mtls` field holds the MtlsDetails value that specifies the mTLS metadata for the connection between the client and the regional external Application Load Balancer. This field is only available if the load balancer uses frontend mutual TLS (mTLS).

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

TlsDetails 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 can be TLS `1.0, 1.1, 1.2, 1.3`, 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 is not using HTTP(S) or the client is not using TLS/SSL encryption.

MtlsDetails field format

Field	Field format	Field type: Required or Optional	Description
clientCertPresent	bool	Optional	`true` if the client has provided a certificate during the TLS handshake; otherwise, `false`.
clientCertChainVerified	bool	Optional	`true` if the client certificate chain is verified against a configured `TrustStore`; otherwise, `false`.
clientCertError	string	Optional	Predefined strings representing the error conditions. For more information about the error strings, see mTLS client validation modes.
clientCertSha256Fingerprint	string	Optional	Base64-encoded SHA-256 fingerprint of the client certificate.
clientCertSerialNumber	string	Optional	The serial number of the client certificate. If the serial number is longer than 50 bytes, the string `client_cert_serial_number_exceeded_size_limit` is added to `client_cert_error`, and the serial number is set to an empty string.
clientCertValidStartTime	string	Optional	Timestamp (RFC 3339 date string format) before which the client certificate is not valid. For example, `2022-07-01T18:05:09+00:00`.
clientCertValidEndTime	string	Optional	Timestamp (RFC 3339 date string format) after which the client certificate is not valid. For example, `2022-07-01T18:05:09+00:00`.
clientCertSpiffeId	string	Optional	The SPIFFE ID from the subject alternative name (SAN) field. If the value is not valid or exceeds 2048 bytes, the SPIFFE ID is set to an empty string. If the SPIFFE ID is longer than 2048 bytes, the string `client_cert_spiffe_id_exceeded_size_limit` is added to `client_cert_error`.
clientCertUriSans	string	Optional	Comma-separated Base64-encoded list of the SAN extensions of type URI. The SAN extensions are extracted from the client certificate. The SPIFFE ID is not included in the `client_cert_uri_sans` field. If the `client_cert_uri_sans` field is longer than 512 bytes, the string `client_cert_uri_sans_exceeded_size_limit` is added to `client_cert_error`, and the comma-separated list is set to an empty string.
clientCertDnsnameSans	string	Optional	Comma-separated Base64-encoded list of the SAN extensions of type DNSName. The SAN extensions are extracted from the client certificate. If the `client_cert_dnsname_sans` field is longer than 512 bytes, the string `client_cert_dnsname_sans_exceeded_size_limit` is added to `client_cert_error`, and the comma-separated list is set to an empty string.
clientCertIssuerDn	string	Optional	Base64-encoded full Issuer field from the certificate. If the `client_cert_issuer_dn` field is longer than 512 bytes, the string `client_cert_issuer_dn_exceeded_size_limit` is added to `client_cert_error`, and `client_cert_issuer_dn` is set to an empty string.
clientCertSubjectDn	string	Optional	Base64-encoded full Subject field from the certificate. If the `client_cert_subject_dn` field is longer than 512 bytes, the string `client_cert_subject_dn_exceeded_size_limit` is added to `client_cert_error`, and `client_cert_subject_dn` is set to an empty string.
clientCertLeaf	string	Optional	The client leaf certificate for an established mTLS connection where the certificate passed validation. Certificate encoding is compliant with RFC 9440: the binary DER certificate is encoded using Base64 (without line breaks, spaces, or other characters outside the Base64 alphabet) and delimited with colons on either side. If `client_cert_leaf` exceeds 16 KB unencoded, the string `client_cert_validated_leaf_exceeded_size_limit` is added to `client_cert_error`, and `client_cert_leaf` is set to an empty string.
clientCertChain	string	Optional	The comma-delimited list of certificates, in standard TLS order, of the client certificate chain for an established mTLS connection where the client certificate passed validation, not including the leaf certificate. Certificate encoding is compliant with RFC 9440. If the combined size of `client_cert_leaf` and `client_cert_chain` before Base64 encoding exceeds 16 KB, the string `client_cert_validated_chain_exceeded_size_limit` is added to `client_cert_error`, and `client_cert_chain` is set to an empty string.

Resource labels

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

Field	Type	Description
`backend_name`	string	The name of the backend instance group or NEG. However, the label is empty for a failed TLS connection.
`backend_scope`	string	The scope of the backend (either a zone name or a region name). Might be `UNKNOWN` whenever `backend_name` is unknown.
`backend_scope_type`	string	The scope of the backend (`REGION`/`ZONE`). Might be `UNKNOWN` whenever `backend_name` is unknown.
`backend_target_name`	string	The name of the backend selected to handle the request, based on the URL map path rule or route rule that matches the request.
`backend_target_type`	string	The type of backend target. Can be `BACKEND_SERVICE`, or `UNKNOWN` is returned if the backend wasn't assigned.
`backend_type`	string	The type of the backend group. Can be `INSTANCE_GROUP`, `NETWORK_ENDPOINT_GROUP`, or `UNKNOWN` is returned if the backend wasn't assigned.
`forwarding_rule_name`	string	The name of the forwarding rule object.
`matched_url_path_rule`	string	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 matches no URL path rules, so it uses the default path rule. `UNKNOWN` indicates an internal error or a failed TLS connection.
`network_name`	string	The name of the load balancer's VPC network.
`project_id`	string	The identifier of the Google Cloud project associated with this resource.
`region`	string	The region in which the load balancer is defined.
`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. It is empty for a failed TLS connection.

proxyStatus error field

The proxyStatus field contains a string that specifies why the load balancer returned an error. There are two parts in the proxyStatus field, proxyStatus error and proxyStatus details. This section describes the strings that are supported in the proxyStatus error field.

The proxyStatus error field is applicable to the following load balancers:

Regional external Application Load Balancer
Cross-region internal Application Load Balancer
Regional internal Application Load Balancer

Filter this table:

proxyStatus error	Description	Common accompanying response codes
`destination_unavailable`	The load balancer considers the backend to be unavailable. For example, recent attempts to communicate with the backend have failed, or a health check might have resulted in a failure.	500, 503
`connection_timeout`	The load balancer's attempt to open a connection to the backend has timed out.	504
`connection_terminated`	The load balancer's connection to the backend ended before a complete response is received. This `proxyStatus error` is returned during any of the following scenarios: The load balancer's connection to the backend ended before a complete response is received. The TLS connection failed on the SSL handshake, and the client didn't establish a connection with the load balancer.	0, 502, 503
`connection_refused`	The load balancer's connection to the backend is refused.	502, 503
`connection_limit_reached`	The load balancer is configured to limit the number of connections it has to the backend, and that limit has been exceeded. This `proxyStatus error` is returned during any of the following scenarios: If any backend is in maintenance mode, the traffic can't be routed to the backend. If the request is locally rate limited. Envoy is handling error conditions such as running out of memory.	502, 503
`destination_not_found`	The load balancer can't determine the appropriate backend to use for this request. For example, the backend might not be configured.	500, 404
`dns_error`	The load balancer encountered a DNS error when trying to find an IP address for the backend hostname.	502, 503
`proxy_configuration_error`	The load balancer encountered an internal configuration error.	500
`proxy_internal_error`	The load balancer encountered an internal error.	0, 500, 502
`proxy_internal_response`	The load balancer generated the response without attempting to connect to the backend.	Any response code depending on the type of problem. For example, the `410` response code means that the backend is unavailable due to payment delinquency.
`http_response_timeout`	The load balancer reached a configured backend service timeout limit while waiting for the complete response from the backend.	504, 408
`http_request_error`	The load balancer encountered an HTTP 4xx error, indicating problems with the client request.	400, 403, 405, 406, 408, 411, 413, 414, 415, 416, 417, or 429
`http_protocol_error`	The load balancer encountered an HTTP protocol error while communicating with the backend.	502
`tls_protocol_error`	The load balancer encountered a TLS error during the TLS handshake.	0
`tls_certificate_error`	The load balancer encountered an error at the time of verifying the certificate presented by the server or by the client when mTLS is enabled.	0
`tls_alert_received`	The load balancer encountered a fatal TLS alert during the TLS handshake.	0

proxyStatus details field

The proxyStatus field contains a string that specifies why the load balancer returned an error. There are two parts in the proxyStatus field, proxyStatus error and proxyStatus details. The proxyStatus details field is optional and is shown only when additional information is available. This section describes the strings that are supported in the proxyStatus details field.

The proxyStatus details field is applicable to the following load balancers:

Regional external Application Load Balancer
Regional internal Application Load Balancer
Cross-region internal Application Load Balancer

Filter this table:

proxyStatus details	Description	Common accompanying response codes
`client_disconnected_before_any_response`	The connection to the client was broken before the load balancer sent any response.	0
`backend_connection_closed`	The backend unexpectedly closed its connection to the load balancer. This can happen if the load balancer is sending traffic to another entity such as a third-party application that has a TCP timeout shorter than the 10-minute (600-second) timeout of the load balancer.	502
`failed_to_connect_to_backend`	The load balancer failed to connect to the backend. This failure includes timeouts during the connection phase.	503
`failed_to_pick_backend`	The load balancer failed to pick a healthy backend to handle the request.	502
`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.
`client_timed_out`	The connection between the load balancer and client exceeded the idle timeout. For more information about regional external Application Load Balancer, see Client HTTP keepalive timeout. For more information about internal Application Load Balancer, see Client HTTP keepalive timeout.	0, 408
`backend_timeout`	The backend timed out while generating a response.	502
`http_protocol_error_from_backend_response`	The backend response contains an HTTP protocol error.	501, 502
`http_protocol_error_from_request`	The client request contains an HTTP protocol error.	400, 503
`http_version_not_supported`	The HTTP protocol version is not supported. Only HTTP 0.9, 1.0, 1.1, and 2.0 are supported.	400
`handled_by_identity_aware_proxy`	This response was generated by Identity-Aware Proxy (IAP) during verifying the identity of the client before allowing access.	200, 302, 400, 401, 403, 500, 502
`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, 404
`ip_detection_failed`	The original IP address couldn't be detected.	Any response code possible depending on the nature of the failure. The value must be from 400 to 599.
`request_body_too_large`	The HTTP request body exceeded the maximum length supported by the load balancer.	413, 507
`request_header_timeout`	The request header timed out because the load balancer didn't receive the complete request within 5 seconds.	408, 504
`denied_by_security_policy`	The load balancer denied this request because of a Google Cloud Armor security policy.	403
`throttled_by_security_policy`	The request was blocked by a Google Cloud Armor throttle rule.	429
`client_cert_chain_invalid_eku`	Either the client certificate or its issuer doesn't have extended key usage that includes clientAuth. 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 10 name constraints. For more information, see Logged errors for closed connections.	0
`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_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_pki_too_large`	The PKI to be used for validation has more than three intermediate certificates that share the same `Subject` and `Subject Public Key Info`. 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_validation_failed`	The client certificate fails validation with the `TrustConfig`. For more information, see Logged errors for closed connections.	0
`client_cert_validation_not_performed`	You have configured mutual TLS without setting up a `TrustConfig`. 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_timed_out`	The time limit exceeded (200 ms) while validating the certificate chain. For more information, see Logged errors for closed connections.	0
`tls_version_not_supported`	The TLS protocol version is recognized but not supported. The error results in a closed TLS connection.	0
`unknown_psk_identity`	Servers send this error when PSK key establishment is required, but the client doesn't provide an acceptable PSK identity. The error results in a closed TLS connection.	0
`no_application_protocol`	Sent by servers when a client "application_layer_protocol_negotiation" extension advertises only protocols that the server doesn't support. See TLS application-layer protocol negotiation extension. The error results in a closed TLS connection.	0
`no_certificate`	No certificate was found. The error results in a closed TLS connection.	0
`bad_certificate`	A certificate is invalid, or it contains signatures that couldn't be verified. The error results in a closed TLS connection.	0
`unsupported_certificate`	A certificate is of an unsupported type. The error results in a closed TLS connection.	0
`certificate_revoked`	A certificate was revoked by its signer. The error results in a closed TLS connection.	0
`certificate_expired`	A certificate has expired or it is not valid. The error results in a closed TLS connection.	0
`certificate_unknown`	Some unspecified issues arose while processing the certificate, rendering it unacceptable. The error results in a closed TLS connection.	0
`unknown_ca`	A valid certificate chain or partial chain was received, but the certificate was not accepted because the CA certificate couldn't be located or matched with a known trust anchor. The error results in a closed TLS connection.	0
`unexpected_message`	An inappropriate message, such as a wrong handshake message or premature application data was received. The error results in a closed TLS connection.	0
`bad_record_mac`	A record is received that can't be deprotected. The error results in a closed TLS connection.	0
`record_overflow`	A `TLSCiphertext` record was received that has a length more than 2¹⁴+256 bytes, or a record was decrypted to a `TLSPlaintext` record with more than 2¹⁴ bytes (or some other negotiated limit). The error results in a closed TLS connection.	0
`handshake_failure`	Unable to negotiate an acceptable set of security parameters given the options available. The error results in a closed TLS connection.	0
`illegal_parameter`	A field in the handshake was incorrect or inconsistent with other fields. The error results in a closed TLS connection.	0
`access_denied`	A valid certificate or PSK was received, but when access control was applied, the client didn't proceed with negotiation. The error results in a closed TLS connection.	0
`decode_error`	A message couldn't be decoded because some fields were out of the specified range, or the length of the message was incorrect. The error results in a closed TLS connection.	0
`decrypt_error`	A handshake (not record layer) cryptographic operation failed, including being unable to correctly verify a signature or validate a finished message or a PSK binder. The error results in a closed TLS connection.	0
`insufficient_security`	A negotiation has failed specifically because the server requires parameters more secure than those supported by the client. The error results in a closed TLS connection.	0
`inappropriate_fallback`	Sent by a server in response to an invalid connection retry attempt from a client. The error results in a closed TLS connection.	0
`user_cancelled`	The user is cancels the handshake for some reason unrelated to a protocol failure. The error results in a closed TLS connection.	0
`missing_extension`	Sent by endpoints that receive a handshake message not containing an extension that is mandatory to send for the offered TLS version or other negotiated parameters. The error results in a closed TLS connection.	0
`unsupported_extension`	Sent by endpoints that receive any handshake message containing an extension known to be prohibited for inclusion in the given handshake message, or including any extensions in `ServerHello` or `Certificate` that was not first offered in the corresponding `ClientHello` or `CertificateRequest`. The error results in a closed TLS connection.	0
`unrecognized_name`	Sent by servers when no server exists that can be identified by the name provided by the client through the "server_name" extension. See TLS extension definitions.	0
`bad_certificate_status_response`	Sent by clients when an invalid or unacceptable OCSP response is provided by the server through the "status_request" extension. See TLS extension definitions. The error results in a closed TLS connection.	0
`load_balancer_configured_resource_limits_reached`	The load balancer has reached the configured resource limits, such as the maximum number of connections.	400, 500, 503

Failed TLS connection log entries

When the TLS connection between the client and the load balancer fails before any backend is selected, log entries record the errors. You can configure the backend services with different log sample rates. When a TLS connection fails, the failed TLS connection log sample rate is the highest sample rate for any backend service. For example, if you have configured two backend services with logging sample rate as 0.3 and 0.5, the failed TLS connection log sample rate is 0.5.

You can identify failed TLS connections by checking for these log entry details:

proxyStatus error type is tls_alert_received, tls_certificate_error, tls_protocol_error, or connection_terminated.
There is no backend information.

The following sample shows a failed TLS log entry with the proxyStatus error field:

   json_payload:    {
   @type: "type.googleapis.com/google.cloud.loadbalancing.type.LoadBalancerLogEntry"
   proxyStatus: "error="tls_alert_received"; details="server_to_client: handshake_failure""
   log_name: "projects/529254013417/logs/mockservice.googleapis.com%20name"
   }
   http_request {
    latency {
      nanos: 12412000
    }
    protocol: "HTTP/1.0"
    remote_ip: "127.0.0.2"
   }
  resource {
    type: "mock_internal_http_lb_rule"
    labels {
      backend_name: ""
      backend_scope: ""
      backend_scope_type: "UNKNOWN"
      backend_target_name: ""
      backend_target_type: "UNKNOWN"
      backend_type: "UNKNOWN"
      forwarding_rule_name: "l7-ilb-https-forwarding-rule-dev"
      matched_url_path_rule: "UNKNOWN"
      network_name: "lb-network"
      region: "REGION"
      target_proxy_name: "l7-ilb-https-proxy-dev"
      url_map_name: ""
    }
  }
  timestamp: "2023-08-15T16:49:30.850785Z"

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.

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`.

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 Cloud Logging API overview.

Monitoring

The load balancer exports monitoring data to Cloud 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

In addition to the predefined dashboards in Cloud Monitoring, you can create custom dashboards, set up alerts, and query the metrics through the Cloud Monitoring API.

Defining alerting policies

You can create alerting policies to monitor the values of metrics and to notify you when those metrics violate a condition.

In the Google Cloud console, go to the Alerting page:
Go to Alerting

If you use the search bar to find this page, then select the result whose subheading is Monitoring.
If you haven't created your notification channels and if you want to be notified, then click Edit Notification Channels and add your notification channels. Return to the Alerting page after you add your channels.
From the Alerting page, select Create policy.
To select the metric, expand the Select a metric menu and then do the following:
1. To limit the menu to relevant entries, enter Regional External Application Load Balancer Rule into the filter bar. If there are no results after you filter the menu, then disable the Show only active resources & metrics toggle.
2. For the Resource type, select Regional External Application Load Balancer Rule.
3. Select a Metric category and a Metric, and then select Apply.
Click Next.
The settings in the Configure alert trigger page determine when the alert is triggered. Select a condition type and, if necessary, specify a threshold. For more information, see Create metric-threshold alerting policies.
Click Next.
Optional: To add notifications to your alerting policy, click Notification channels. In the dialog, select one or more notification channels from the menu, and then click OK.
Optional: Update the Incident autoclose duration. This field determines when Monitoring closes incidents in the absence of metric data.
Optional: Click Documentation, and then add any information that you want included in a notification message.
Click Alert name and enter a name for the alerting policy.
Click Create Policy.

For more information, see Alerting policies.

Defining Cloud Monitoring custom dashboards

You can create custom Cloud Monitoring dashboards for the load balancer's metrics:

In the Google Cloud console, go to the Monitoring page.

Go to Monitoring
Select Dashboards > Create Dashboard.
Click Add Chart, and then give the chart a title.
To identify the time series to be displayed, choose a resource type and metric type:
1. In the Resource & Metric section, click the chart, and then in the Select a metric section, select from the available options:
2. For a regional external Application Load Balancer, select the resource type Regional External Application Load Balancer Rule.
3. Click Apply.
To specify monitoring filters, click Filters > Add filter.
Click Save.

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 regional 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/external/regional/request_count`	The number of requests served by the regional external Application Load Balancer.
Request bytes count	`https/external/regional/request_bytes`	The number of bytes sent as requests from clients to the regional external Application Load Balancer.
Response bytes count	`https/external/regional/response_bytes`	The number of bytes sent as responses from the regional external Application Load Balancer to the client.
Total latencies	`https/external/regional/total_latencies`	A distribution of the latency, in milliseconds. Latency is measured from the time when the proxy receives the first byte of the request to the time when the proxy sends the last byte of the response.
Backend latencies	`https/external/regional/backend_latencies`	A distribution of the latency, in milliseconds. Latency is measured from the time when the proxy sends the first byte of the request to the backend to the time when the proxy receives the last byte of the response from the backend.

Filtering dimensions for metrics

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

Metrics are aggregated for each regional external Application Load Balancer. You can filter aggregated metrics by using the following dimensions for resource.type="http_external_regional_lb_rule".

Filter this table:

Property	Description
`backend_name`	The name of the backend instance group or NEG.
`backend_scope`	The scope of the backend (either a zone name or a region name). Might be `UNKNOWN` whenever `backend_name` is unknown.
`backend_scope_type`	The scope of the backend (`REGION`/`ZONE`). Might be `UNKNOWN` whenever `backend_name` is unknown.
`backend_target_name`	The name of the backend selected to handle the request, based on the URL map path rule or route rule that matches the request.
`backend_target_type`	The type of backend target. Can be `BACKEND_SERVICE`, or `UNKNOWN` is returned if the backend wasn't assigned.
`backend_type`	The type of the backend group. Can be `INSTANCE_GROUP`, `NETWORK_ENDPOINT_GROUP`, or `UNKNOWN` is returned if the backend wasn't assigned.
`forwarding_rule_name`	The name of the forwarding rule object.
`matched_url_path_rule`	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 it uses the default path rule. `UNKNOWN` indicates an internal error.
`network_name`	The name of the load balancer's VPC network.
`project_id`	The identifier of the Google Cloud project associated with this resource.
`region`	The region in which the load balancer is defined.
`target_proxy_name`	The name of the target proxy object referenced by the forwarding rule.
`url_map_name`	The name of the URL map object configured to select a backend service.

What's next

Read conceptual information about external Application Load Balancers.