Internal Application Load Balancer logging and monitoring

This document provides you with the information that you need to understand logging and monitoring metrics for internal Application Load Balancers. The logging and monitoring metrics for both regional internal Application Load Balancers and cross-region internal Application Load Balancers are the same.

Logging

You can enable logging on a per-backend service basis. A single internal Application Load Balancer's URL map can reference more than one backend service. You might need to enable logging for multiple backend services depending on your configuration.

Logs sampling and collection

Google Cloud samples the packets that leave and enter load balancer backend virtual machine (VM) instances. Those sampled packets are processed to generate logs.

Not every packet is sampled. Google Cloud samples a variable subset of packets depending on the amount of traffic on the physical host. The lowest possible sampling rate is one out of 1,024 packets. The sampling rate is dynamically controlled by Google Cloud. You cannot adjust the sampling rate.

The packet sampling interacts with firewall rules in the following ways:

Packets are sampled before egress firewall rules are applied.
Packets are sampled after ingress firewall rules are applied.

After packet sampling, Google Cloud processes the sampled packets according to the following procedure:

Aggregation: Sampled packets are aggregated over a five-second interval to produce a single flow entry.
Configurable (secondary) log sampling: This is a second sampling process, sampling the flows. You control the fraction of the flow entries that are emitted as log entries according to the logConfig.sampleRate parameter. When logConfig.sampleRate is 1.0 (100%), this means that all of the sampled packets are processed.
Write to logging: The log entries are 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 flow logs. When new optional fields are added to the record format, the flow 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 an existing backend service.

Enabling logging on an existing backend service

For regional internal Application Load Balancers, use the following steps:

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.
Click Advanced configurations (Session affinity, connection draining timeout).
Click Enable logging.
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

To update the backend service to enable logging, use the gcloud compute backend-services update command.

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

where

--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 no requests are logged and 1.0 means 100% of 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.

For cross-region internal Application Load Balancers, use the following steps:

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.
Click Advanced configurations (Session affinity, connection draining timeout).
Click Enable logging.
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

To update the backend service to enable logging, use the gcloud compute backend-services update command.

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

where

--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 no requests are logged and 1.0 means 100% of 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.

After you enable logging on the backend service, each HTTP(S) request is logged by using Cloud Logging.

How to view logs

To view logs, in the Google Cloud console, go to the Logs Explorer page.

Internal Application Load Balancer logs are indexed first by network and then by region.

To see logs for all internal Application Load Balancers, in the first pull-down menu, select Internal Application Load Balancer Rule.
To see logs for only one network, select Internal Application Load Balancer Rule, and then select the name of a network.
To see logs for just one region of the network, select Internal Application Load Balancer Rule > NETWORK > REGION.

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.

You can configure export of logs-based metrics for resource logs (resource.type="internal_http_lb_rule"). The metrics created are based on the "Internal Application Load Balancer Rule" resource, which is available under Cloud Monitoring dashboards:

Go to Monitoring

What is logged

Internal 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, and optional fields that add additional information about your HTTP(S) traffic. Optional fields can be omitted to save storage costs. Log entries contain the following types of information:

General information shown in most Google Cloud logs, such as severity, project ID, project number, and timestamp as described in the LogEntry.
HttpRequest log fields.

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	Type	Field type: Required or Optional	Description
Field	Type	Field type: Required or Optional	Description	`logName`	string	Required	The resource name of the log to which this log entry belongs. In the form `"projects/PROJECT_ID/logs/requests"`.
`timestamp`	string	Required	The time at which the request began.
`severity`	LogSeverity format	Required	The severity of the log entry. Defaults to `LogSeverity.DEFAULT`.
`httpRequest`	HttpRequest object	Required	An HttpRequest proto that describes the HTTP(S) request being logged.
`trace`	string	Required	The resource name of the trace associated with the log entry, if any. If it contains a relative resource name, the name is assumed to be relative to `https://tracing.googleapis.com`. Example: `projects/PROJECT_ID/traces/06796866738c859f2f19b7cfb3214824`. Internal Application Load Balancers don't support this field.
`spanId`	string	Required	The span ID within the trace associated with the log entry. For Trace spans, this string has the same format that the Trace API v2 uses: a 16-character hexadecimal encoding of an 8-byte array, such as `000000000000004a`. Internal Application Load Balancers don't support this field.
`resource`	MonitoredResource object	Required	The monitored resource that produced this log entry. The `MonitoredResourceDescriptor` object describes the schema of a `MonitoredResource` object by using a type name and a set of labels. For example, monitored resource descriptors for internal Application Load Balancers have a resource type of `internal_http_lb_rule` and use resource labels to identify the actual resource and its attributes. For a list of resource labels, see the Resource labels for `resource.type="internal_http_lb_rule"`.
jsonPayload	object (Struct format)	Required	The log entry payload that is expressed as a JSON object. The JSON object contains the following fields: `tls` `proxyStatus` `backendTargetProjectNumber` `serviceDirectoryService` `cloudFitExperiment` `cloudFitFault` `serviceExtensionInfo` `mtls`
	string	Required	The `proxyStatus` field holds a string that specifies why the internal Application Load Balancer returned the `HttpRequest.status`. This field is populated only when the proxy returns an error code. 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
	string	Required	The `backendTargetProjectNumber` field holds the project number that identifies the owner of the backend service or backend bucket.
	string	Required	The `serviceDirectoryService` field holds the name of the Service Directory service on which the Cloud FIT fault was configured.
	string	Required	The `cloudFitExperiment` field holds the name of the Cloud FIT experiment.
	string	Required	The `cloudFitFault` field holds the name of the fault injected by a Cloud FIT fault experiment in this request path.
	ServiceExtensionInfo	Required	The `serviceExtensionInfo` field stores information about the gRPC streams from the load balancer to Service Extensions. For more information, see what is logged for callout extensions.
	TlsDetails	Optional	The `tls` field holds the TlsDetails that specifies the TLS metadata for the connection between the client and the internal 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 internal Application Load Balancer. This field is only available if the load balancer uses frontend mutual TLS (mTLS).

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.

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 is generating a client (4xx) response on the client's behalf.	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 are invalid.	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 timeout was exceeded. The timeout value is 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"

Resource labels

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

Field	Type	Description
`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.
`url_map_name`	string	The name of the URL map object configured to select a backend service.
`forwarding_rule_name`	string	The name of the forwarding rule object.
`target_proxy_name`	string	The name of the target proxy object referenced by the forwarding rule.
`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.
`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 (`BACKEND_SERVICE` / `UNKNOWN`).
`backend_name`	string	The name of the backend instance group or NEG.
`backend_type`	string	The type of backend, either an instance group or a NEG, or unknown. Cloud Logging logs requests when the `backend_type` is `UNKNOWN` even if logging is disabled. For example, if a client closes the connection to the load balancer before the load balancer can pick a backend, the `backend_type` is set to `UNKNOWN` and the request is logged. These logs provide useful debugging information about client requests that were closed because the load balancer could not select a backend.
`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.

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

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

Go to Logs Explorer
Click the Show query toggle to enable the query editor.

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.

Monitoring

Internal Application Load Balancers export monitoring data to Monitoring.

Monitoring metrics can be used for the following purposes:

Evaluating a load balancer's configuration, usage, and performance
Troubleshooting problems
Improving resource utilization and user experience

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

Viewing Cloud Monitoring metrics

Console

To view the metrics for a monitored resource by using the Metrics Explorer, do the following:

In the Google Cloud console, go to the Metrics explorer page:
Go to Metrics explorer

If you use the search bar to find this page, then select the result whose subheading is Monitoring.
In the Metric element, expand the Select a metric menu, enter Internal Application Load Balancer Rule in the filter bar, and then use the submenus to select a specific resource type and metric:
1. In the Active resources menu, select Internal Application Load Balancer Rule.
2. To select a metric, use the Active metric categories and Active metrics menus.
3. Click Apply.
To remove time series from the display, use the Filter element.
To combine time series, use the menus on the Aggregation element. For example, to display the CPU utilization for your VMs, based on their zone, set the first menu to Mean and the second menu to zone.

All time series are displayed when the first menu of the Aggregation element is set to Unaggregated. The default settings for the Aggregation element are determined by the metric type you selected.
For quota and other metrics that report one sample per day, do the following:
1. In the Display pane, set the Widget type to Stacked bar chart.
2. Set the time period to at least one week.

Defining alerting policies

Console

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 Internal 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 Internal 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 Monitoring custom dashboards

Console

You can create custom Monitoring dashboards over internal Application Load Balancer metrics:

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

Go to Monitoring
Select Dashboards > Create Dashboard.
Click Add Chart.
Give the chart a title.
Select metrics and filters. For metrics, the resource type is Internal HTTP/S Load Balancer.
Click Save.

Metric reporting frequency and retention

Metrics for the load balancers are exported to 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 for internal Application Load Balancers

The following metrics for internal Application Load Balancers are reported into Monitoring:

Metric	FQDN	Description
Request count	`loadbalancing.googleapis.com/https/internal/request_count`	The number of requests served by the internal Application Load Balancer.
Request bytes count	`loadbalancing.googleapis.com/https/internal/request_bytes`	The number of bytes sent as requests from clients to the internal Application Load Balancer.
Response bytes count	`loadbalancing.googleapis.com/https/internal/response_bytes`	The number of bytes sent as responses from the internal HTTP(S) load balancer to the client.
Total latencies	`loadbalancing.googleapis.com/https/internal/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	`loadbalancing.googleapis.com/https/internal/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 internal Application Load Balancer metrics

Metrics are aggregated for each internal Application Load Balancer. You can filter aggregated metrics by the following dimensions.

Property	Description
BACKEND_SCOPE	The Google Cloud zone or region of the backend group that served the client request, or a special string for cases in which the backend group wasn't assigned. Examples: `us-central1-a`, `europe-west1-b`, `asia-east1`, `UNKNOWN`.
PROXY_REGION	Region of the internal Application Load Balancer, client, and backend. Examples: `us-central1`, `europe-west1` or `asia-east1`.
BACKEND	The name of the backend instance group or NEG that served the client request.
BACKEND_TARGET	The name of the backend service that served the client request.
MATCHED_URL_RULE	The URL map path rule or route rule that matched the prefix of the client HTTP(S) request (up to 50 characters).

The Response code class fraction metric is supported for the entire load balancer. No further granularity is supported.

What's next

Read conceptual information about internal Application Load Balancers.
Create an internal Application Load Balancer.
See Internal load balancing and DNS names for available DNS name options your load balancer can use.