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Application logging

docs/root/configuration/observability/application_logging.rst

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.. _config_application_logs:

Application logging

Envoy and its filters write application logs for debuggability. Envoy can be configured to output application logs in a format that is compatible with common log viewers. This section documents how Envoy can be configured to enable integration with each log viewer.

Stackdriver Logging with GKE

Stackdriver Logging <https://cloud.google.com/logging/>_ can read logs from containers running on Google Kubernetes Engine <https://cloud.google.com/kubernetes-engine/>_. Envoy should be configured with the following :ref:command line options <operations_cli>:

  • --log-format '%L%m%d %T.%e %t envoy/%@] [%t][%n]%v': Logs are formatted in glog <https://github.com/google/glog>_ format, allowing Stackdriver to parse the log severity and timestamp.
  • --log-format-escaped: Each string that is logged will be printed in a single line. C-style escape sequences (such as \n) will be escaped and prevent a single string from spanning multiple lines. This ensures each log line is structured with the glog prefix.
  • The --log-path flag does not need to be set, since Stackdriver can read logs from STDERR.
  • The --log-level flag can be set to control the log severity logged to Stackdriver.

Reference documentation <https://cloud.google.com/run/docs/logging#container-logs>_ for Stackdriver on GKE.

Printing logs in JSON format

It is possible to use the bootstrap config :ref:json_format <envoy_v3_api_field_config.bootstrap.v3.Bootstrap.ApplicationLogConfig.LogFormat.json_format> to print the logs in custom JSON format. The json format struct can support all the format flags that are specified in :ref:command line options <operations_cli>, except for the %v and %_ flags, as they may break the JSON structure log. Instead, use the %j flag. Example:

.. code-block:: yaml

application_log_config: log_format: json_format: Timestamp: "%Y-%m-%dT%T.%F" ThreadId: "%t" SourceLine: "%s:%#" Level: "%l" Message: "%j" FixedValue: "SomeFixedValue"

.. note:: Setting both application_log_config.log_format and CLI option --log-format is not allowed, and will cause a bootstrap error.