Logging

When your app is deployed to AWS Lambda, logging to stdout logs are sent to CloudWatch logs. You can configure the log verbosity level Lambda writes to CloudWatch logs. These are the Jets defaults.

config/jets/deploy.rb

Jets.deploy.configure do
  config.lambda.function.logging_config = {
    ApplicationLogLevel: "INFO",
    LogFormat: "JSON", # Text | JSON
    SystemLogLevel: "WARN"
  }
end

Important: To set log levels, you must use LogFormat: "JSON".

  • Application Log Levels: TRACE DEBUG INFO WARN ERROR FATAL
  • System Log Levels: DEBUG INFO WARN

The System WARN level removes initStart, runtimeDone, report logs which usually look like this

START RequestId: aef5f99f-3eea-4963-bc17-02717248a83f Version: $LATEST
...
END RequestId: aef5f99f-3eea-4963-bc17-02717248a83f
REPORT RequestId: aef5f99f-3eea-4963-bc17-02717248a83f Duration: 9.69 ms Billed Duration: 10 ms Memory Size: 1536 MB Max Memory Used: 405 MB

To reset it to default AWS Lambda logging behavior, use:

config/jets/deploy.rb

Jets.deploy.configure do
  config.lambda.function.logging_config = {
    LogFormat: "Text",
  }
end

Note, you cannot set log levels when using LogFormat: "Text".

Related:

Prewarm Logging

When using LogFormat: "Text", prewarming requests can add noise to the logs.

If you want to see the noisy prewarming logs.

config/jets/deploy.rb

Jets.deploy.configure do
  config.lambda.function.logging_config = {
    LogFormat: "Text",
  }
  config.prewarm.quiet = false
end

The prewarming request logs then look like this

$ jets logs -f
START RequestId: aef5f99f-3eea-4963-bc17-02717248a83f Version: $LATEST
Prewarm request: {"boot_at":"2024-04-26 02:00:36 UTC","gid":"7ac4ad98","prewarm_at":"2024-04-26 02:17:59 UTC","prewarm_count":18}
END RequestId: aef5f99f-3eea-4963-bc17-02717248a83f
REPORT RequestId: aef5f99f-3eea-4963-bc17-02717248a83f Duration: 9.69 ms Billed Duration: 10 ms Memory Size: 1536 MB Max Memory Used: 405 MB

Rails Logging Format

The Rails logging format includes it’s own timestamp and process info.

$ jets logs -f
I, [2024-04-26T03:14:22.572735 #9] INFO -- : [a989a1f7-7f83-4984-bf52-dd86d9c96c0c] Started GET "/" for 66.234.208.210 at 2024-04-26 03:14:22 +0000
I, [2024-04-26T03:14:22.573489 #9] INFO -- : [a989a1f7-7f83-4984-bf52-dd86d9c96c0c] Processing by ApplicationController#home as HTML
I, [2024-04-26T03:14:22.776744 #9] INFO -- : [a989a1f7-7f83-4984-bf52-dd86d9c96c0c] Completed 200 OK in 203ms (Views: 118.3ms | ActiveRecord: 79.6ms | Allocations: 52194)

If you want to remove Rails timestamp and pid

config/environments/production.rb

Rails.application.configure do
  # Use default logging formatter so that PID and timestamp are not suppressed.
  config.log_formatter = ::Logger::Formatter.new

  # Uncomment to also remove the id hash, but SimpleFormatter strips the leading spaces
  # logger = ActiveSupport::Logger.new(STDOUT)
  # logger.formatter = ActiveSupport::Logger::SimpleFormatter.new
  # config.logger = logger
end

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