Configuring Task Log Output and Retention

Task environment variables that influence logging

You can modify the destination and log retention of task logs by specifying any of the following environment variables within the task definition:

Environment Variable Default Short Description
CONTAINER_LOGGER_DESTINATION_TYPE logrotate Where the task logs should be directed: either the task’s sandbox or journald.
CONTAINER_LOGGER_LOGROTATE_MAX_STDOUT_SIZE 2MB The maximum size of the stdout file in the sandbox before log rotation is triggered.
CONTAINER_LOGGER_LOGROTATE_STDOUT_OPTIONS rotate 9 Options to pass to logrotate when rotating the stdout file.
CONTAINER_LOGGER_LOGROTATE_MAX_STDERR_SIZE 2MB The maximum size of the stderr file in the sandbox before log rotation is triggered.
CONTAINER_LOGGER_LOGROTATE_STDERR_OPTIONS rotate 9 Options to pass to logrotate when rotating the stderr file.
CONTAINER_LOGGER_EXTRA_LABELS "{}" Extra key-value pairs to tag each log line when outputting to journald.


WARNING: Specifying invalid values for these options will cause the task launch to fail.

Destination Type

The CONTAINER_LOGGER_DESTINATION_TYPE takes three possible arguments:

  • logrotate (default)
  • journald
  • journald+logrotate

The use of journald options is not recommended, due to journald performance issues. When enabled, logs are piped directly into the node’s journald, along with some labels like the AGENT_ID, EXECUTOR_ID, and CONTAINER_ID.

The logrotate option will place logs (files named stdout and stderr) inside the task sandbox and create additional files for rotating these logs (*.logrotate.conf and *.logrotate.state).

See the Logging API for information on how to read these logs.

Max Sizes

The CONTAINER_LOGGER_LOGROTATE_MAX_STDOUT_SIZE and CONTAINER_LOGGER_LOGROTATE_MAX_STDERR_SIZE options control the maximum size of these log files. Upon reaching this threshold, logrotation is triggered.

Sizes must be an integer of less than 2^64 and must be suffixed with a unit such as B (bytes), KB, MB, GB, or TB. There should be no whitespace between the integer and unit.


  • 2MB
  • 1234B
  • 1TB

IMPORTANT: The hard cap on size is 2^64 bytes. Attempting to specify a higher value (for example, 2^64 TB) will lead to undetermined results.

Logrotate Options

The CONTAINER_LOGGER_LOGROTATE_STDOUT_OPTIONS and CONTAINER_LOGGER_LOGROTATE_STDERR_OPTIONS options control the parameters passed to logrotate for each rotation. There are no restrictions on arguments. Refer to the man page for possible values.

Each logrotate rule should be newline (\n) separated. For example:

  • rotate 10\ncompress\ndelaycompress
  • daily\nmaxage 10\nnomail

Some rules are unnecessary or will be overriden:

  • Time-based rotation will not work as expected. Rotation is triggered based purely on how much has been written. So if rotation is set to fire at 2MB, but less than 2MB is written, then rotation will never occur.
  • copy and copytruncate are not necessary because the log files will not be written to while rotating. This means no log lines can be lost (although they can be cut into separate files if too long).