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observability.md

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Observability Options

Logging

Consul Template can print verbose debugging output. To set the log level for Consul Template, use the -log-level flag:

$ consul-template -log-level info ...

Or set it via the CONSUL_TEMPLATE_LOG_LEVEL environment variable.

<timestamp> [INFO] (cli) received redis from Watcher
<timestamp> [INFO] (cli) invoking Runner
# ...

You can also specify the level as debug:

$ consul-template -log-level debug ...
<timestamp> [DEBUG] (cli) creating Runner
<timestamp> [DEBUG] (cli) creating Consul API client
<timestamp> [DEBUG] (cli) creating Watcher
<timestamp> [DEBUG] (cli) looping for data
<timestamp> [DEBUG] (watcher) starting watch
<timestamp> [DEBUG] (watcher) all pollers have started, waiting for finish
<timestamp> [DEBUG] (redis) starting poll
<timestamp> [DEBUG] (service redis) querying Consul with &{...}
<timestamp> [DEBUG] (service redis) Consul returned 2 services
<timestamp> [DEBUG] (redis) writing data to channel
<timestamp> [DEBUG] (redis) starting poll
<timestamp> [INFO] (cli) received redis from Watcher
<timestamp> [INFO] (cli) invoking Runner
<timestamp> [DEBUG] (service redis) querying Consul with &{...}
# ...

Logging to file

Consul Template can log to file as well. Particularly useful in use cases where it's not trivial to capture stdout and/or stderr like for example when Consul Template is deployed as a Windows Service.

These are the relevant CLI flags:

  • -log-file - writes all the Consul Template log messages to a file. This value is used as a prefix for the log file name. The current timestamp is appended to the file name. If the value ends in a path separator, consul-template- will be appended to the value. If the file name is missing an extension, .log is appended. For example, setting log-file to /var/log/ would result in a log file path of /var/log/consul-template-{timestamp}.log. log-file can be combined with -log-rotate-bytes and -log-rotate-duration for a fine-grained log rotation experience.

  • -log-rotate-bytes - to specify the number of bytes that should be written to a log before it needs to be rotated. Unless specified, there is no limit to the number of bytes that can be written to a log file.

  • -log-rotate-duration - to specify the maximum duration a log should be written to before it needs to be rotated. Must be a duration value such as 30s. Defaults to 24h.

  • -log-rotate-max-files - to specify the maximum number of older log file archives to keep. Defaults to 0 (no files are ever deleted). Set to -1 to discard old log files when a new one is created.