Accessing Amazon CloudWatch logs for AWS Lambda - AWS Lambda

Accessing Amazon CloudWatch logs for AWS Lambda

AWS Lambda automatically monitors Lambda functions on your behalf, reporting metrics through Amazon CloudWatch. To help you troubleshoot failures in a function, after you set up permissions, Lambda logs all requests handled by your function and also automatically stores logs generated by your code through Amazon CloudWatch Logs.

You can insert logging statements into your code to help you validate that your code is working as expected. Lambda automatically integrates with CloudWatch Logs and pushes all logs from your code to a CloudWatch Logs group associated with a Lambda function, which is named /aws/lambda/<function name>.

You can view logs for Lambda functions using the Lambda console, the CloudWatch console, the AWS Command Line Interface (AWS CLI), or the CloudWatch API.

Note

It may take 5 to 10 minutes for logs to show up after a function invocation.

Prerequisites

Your execution role needs permission to upload logs to CloudWatch Logs. You can add CloudWatch Logs permissions using the AWSLambdaBasicExecutionRole AWS managed policy provided by Lambda. To add this policy to your role, run the following command:

aws iam attach-role-policy --role-name your-role --policy-arn arn:aws:iam::aws:policy/service-role/AWSLambdaBasicExecutionRole

For more information, see AWS managed policies for Lambda features.

Pricing

There is no additional charge for using Lambda logs; however, standard CloudWatch Logs charges apply. For more information, see CloudWatch pricing.

Using the Lambda console

To view logs using the Lambda console
  1. Open the Functions page of the Lambda console.

  2. Choose a function.

  3. Choose Monitor.

  4. Choose View logs in CloudWatch.

Using the AWS Command Line Interface

The AWS CLI is an open-source tool that enables you to interact with AWS services using commands in your command line shell. To complete the steps in this section, you must have the following:

You can use the AWS CLI to retrieve logs for an invocation using the --log-type command option. The response contains a LogResult field that contains up to 4 KB of base64-encoded logs from the invocation.

Example retrieve a log ID

The following example shows how to retrieve a log ID from the LogResult field for a function named my-function.

aws lambda invoke --function-name my-function out --log-type Tail

You should see the following output:

{ "StatusCode": 200, "LogResult": "U1RBUlQgUmVxdWVzdElkOiA4N2QwNDRiOC1mMTU0LTExZTgtOGNkYS0yOTc0YzVlNGZiMjEgVmVyc2lvb...", "ExecutedVersion": "$LATEST" }
Example decode the logs

In the same command prompt, use the base64 utility to decode the logs. The following example shows how to retrieve base64-encoded logs for my-function.

aws lambda invoke --function-name my-function out --log-type Tail \ --query 'LogResult' --output text | base64 -d

You should see the following output:

START RequestId: 57f231fb-1730-4395-85cb-4f71bd2b87b8 Version: $LATEST "AWS_SESSION_TOKEN": "AgoJb3JpZ2luX2VjELj...", "_X_AMZN_TRACE_ID": "Root=1-5d02e5ca-f5792818b6fe8368e5b51d50;Parent=191db58857df8395;Sampled=0"",ask/lib:/opt/lib", END RequestId: 57f231fb-1730-4395-85cb-4f71bd2b87b8 REPORT RequestId: 57f231fb-1730-4395-85cb-4f71bd2b87b8 Duration: 79.67 ms Billed Duration: 80 ms Memory Size: 128 MB Max Memory Used: 73 MB

The base64 utility is available on Linux, macOS, and Ubuntu on Windows. macOS users may need to use base64 -D.

Example get-logs.sh script

In the same command prompt, use the following script to download the last five log events. The script uses sed to remove quotes from the output file, and sleeps for 15 seconds to allow time for the logs to become available. The output includes the response from Lambda and the output from the get-log-events command.

Copy the contents of the following code sample and save in your Lambda project directory as get-logs.sh.

The cli-binary-format option is required if you're using AWS CLI version 2. To make this the default setting, run aws configure set cli-binary-format raw-in-base64-out. For more information, see AWS CLI supported global command line options.

#!/bin/bash aws lambda invoke --function-name my-function --cli-binary-format raw-in-base64-out --payload '{"key": "value"}' out sed -i'' -e 's/"//g' out sleep 15 aws logs get-log-events --log-group-name /aws/lambda/my-function --log-stream-name stream1 --limit 5
Example macOS and Linux (only)

In the same command prompt, macOS and Linux users may need to run the following command to ensure the script is executable.

chmod -R 755 get-logs.sh
Example retrieve the last five log events

In the same command prompt, run the following script to get the last five log events.

./get-logs.sh

You should see the following output:

{ "StatusCode": 200, "ExecutedVersion": "$LATEST" } { "events": [ { "timestamp": 1559763003171, "message": "START RequestId: 4ce9340a-b765-490f-ad8a-02ab3415e2bf Version: $LATEST\n", "ingestionTime": 1559763003309 }, { "timestamp": 1559763003173, "message": "2019-06-05T19:30:03.173Z\t4ce9340a-b765-490f-ad8a-02ab3415e2bf\tINFO\tENVIRONMENT VARIABLES\r{\r \"AWS_LAMBDA_FUNCTION_VERSION\": \"$LATEST\",\r ...", "ingestionTime": 1559763018353 }, { "timestamp": 1559763003173, "message": "2019-06-05T19:30:03.173Z\t4ce9340a-b765-490f-ad8a-02ab3415e2bf\tINFO\tEVENT\r{\r \"key\": \"value\"\r}\n", "ingestionTime": 1559763018353 }, { "timestamp": 1559763003218, "message": "END RequestId: 4ce9340a-b765-490f-ad8a-02ab3415e2bf\n", "ingestionTime": 1559763018353 }, { "timestamp": 1559763003218, "message": "REPORT RequestId: 4ce9340a-b765-490f-ad8a-02ab3415e2bf\tDuration: 26.73 ms\tBilled Duration: 27 ms \tMemory Size: 128 MB\tMax Memory Used: 75 MB\t\n", "ingestionTime": 1559763018353 } ], "nextForwardToken": "f/34783877304859518393868359594929986069206639495374241795", "nextBackwardToken": "b/34783877303811383369537420289090800615709599058929582080" }

Runtime function logging

To debug and validate that your code is working as expected, you can output logs with the standard logging functionality for your programming language. The Lambda runtime uploads your function's log output to CloudWatch Logs. For language-specific instructions, see the following topics:

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