AWS Lambda
Developer Guide

AWS Lambda Function Logging in Ruby

Your Lambda function comes with a CloudWatch Logs log group, with a log stream for each instance of your function. The runtime sends details about each invocation to the log stream, and relays logs and other output from your function's code.

To view your Lambda function's logs

  1. Open the Logs page of the CloudWatch console.

  2. Choose the log group for your function (/aws/lambda/function-name).

  3. Choose the first stream in the list.

To output logs from your function code, you can use puts statements, or any logging library that writes to stdout or stderr.

To get logs for an invocation from the command line, use the --log-type option. The response includes a LogResult field that contains up to 4 KB of base64-encoded logs from the invocation.

$ aws lambda invoke --function-name ruby-function out --log-type Tail { "StatusCode": 200, "LogResult": "U1RBUlQgUmVxdWVzdElkOiA4N2QwNDRiOC1mMTU0LTExZTgtOGNkYS0yOTc0YzVlNGZiMjEgVmVyc2lvb...", "ExecutedVersion": "$LATEST" }

You can use the base64 utility to decode the logs.

$ aws lambda invoke --function-name ruby-function out --log-type Tail \ --query 'LogResult' --output text | base64 -d START RequestId: 8e827ab1-f155-11e8-b06d-018ab046158d Version: $LATEST Processing event... END RequestId: 8e827ab1-f155-11e8-b06d-018ab046158d REPORT RequestId: 8e827ab1-f155-11e8-b06d-018ab046158d Duration: 29.40 ms Billed Duration: 100 ms Memory Size: 128 MB Max Memory Used: 19 MB

base64 is available on Linux, macOS, and Ubuntu on Windows. For macOS, the command is base64 -D.