Amazon Lambda function logging in Java - Amazon Lambda
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Amazon Lambda function logging in Java

Amazon Lambda automatically monitors Lambda functions and sends log entries to Amazon CloudWatch. Your Lambda function comes with a CloudWatch Logs log group and a log stream for each instance of your function. The Lambda runtime environment sends details about each invocation and other output from your function's code to the log stream. For more information about CloudWatch Logs, see Using Amazon CloudWatch logs with Amazon Lambda.

To output logs from your function code, you can use methods on java.lang.System, or any logging module that writes to stdout or stderr.

Creating a function that returns logs

To output logs from your function code, you can use methods on java.lang.System, or any logging module that writes to stdout or stderr. The aws-lambda-java-core library provides a logger class named LambdaLogger that you can access from the context object. The logger class supports multiline logs.

The following example uses the LambdaLogger logger provided by the context object.

// Handler value: example.Handler public class Handler implements RequestHandler<Object, String>{ Gson gson = new GsonBuilder().setPrettyPrinting().create(); @Override public String handleRequest(Object event, Context context) { LambdaLogger logger = context.getLogger(); String response = new String("SUCCESS"); // log execution details logger.log("ENVIRONMENT VARIABLES: " + gson.toJson(System.getenv())); logger.log("CONTEXT: " + gson.toJson(context)); // process event logger.log("EVENT: " + gson.toJson(event)); return response; } }
Example log format
START RequestId: 6bc28136-xmpl-4365-b021-0ce6b2e64ab0 Version: $LATEST ENVIRONMENT VARIABLES: { "_HANDLER": "example.Handler", "AWS_EXECUTION_ENV": "AWS_Lambda_java8", "AWS_LAMBDA_FUNCTION_MEMORY_SIZE": "512", ... } CONTEXT: { "memoryLimit": 512, "awsRequestId": "6bc28136-xmpl-4365-b021-0ce6b2e64ab0", "functionName": "java-console", ... } EVENT: { "records": [ { "messageId": "19dd0b57-xmpl-4ac1-bd88-01bbb068cb78", "receiptHandle": "MessageReceiptHandle", "body": "Hello from SQS!", ... } ] } END RequestId: 6bc28136-xmpl-4365-b021-0ce6b2e64ab0 REPORT RequestId: 6bc28136-xmpl-4365-b021-0ce6b2e64ab0 Duration: 198.50 ms Billed Duration: 200 ms Memory Size: 512 MB Max Memory Used: 90 MB Init Duration: 524.75 ms

The Java runtime logs the START, END, and REPORT lines for each invocation. The report line provides the following details:

REPORT line data fields
  • RequestId – The unique request ID for the invocation.

  • Duration – The amount of time that your function's handler method spent processing the event.

  • Billed Duration – The amount of time billed for the invocation.

  • Memory Size – The amount of memory allocated to the function.

  • Max Memory Used – The amount of memory used by the function.

  • Init Duration – For the first request served, the amount of time it took the runtime to load the function and run code outside of the handler method.

  • XRAY TraceId – For traced requests, the Amazon X-Ray trace ID.

  • SegmentId – For traced requests, the X-Ray segment ID.

  • Sampled – For traced requests, the sampling result.

Using Lambda advanced logging controls with Java

To give you more control over how your functions’ logs are captured, processed, and consumed, you can configure the following logging options for supported Java runtimes:

  • Log format - select between plain text and structured JSON format for your function’s logs

  • Log level - for logs in JSON format, choose the detail level of the logs Lambda sends to CloudWatch, such as ERROR, DEBUG, or INFO

  • Log group - choose the CloudWatch log group your function sends logs to

For more information about these logging options, and instructions on how to configure your function to use them, see Configuring advanced logging controls for Lambda functions.

To use the log format and log level options with your Java Lambda functions, see the guidance in the following sections.

Using structured JSON log format with Java

If you select JSON for your function's log format, Lambda will send logs output using the LambdaLogger class as structured JSON. Each JSON log object contains at least four key value pairs with the following keys:

  • "timestamp" - the time the log message was generated

  • "level" - the log level assigned to the message

  • "message" - the contents of the log message

  • "AWSrequestId" - the unique request ID for the function invocation

Depending on the logging method you use, log outputs from your function captured in JSON format can also contain additional key value pairs.

To assign a level to logs you create using the LambdaLogger logger, you need to provide a LogLevel argument in your logging command as shown in the following example.

Example Java logging code
LambdaLogger logger = context.getLogger(); logger.log("This is a debug log", LogLevel.DEBUG);

This log output by this example code would be captured in CloudWatch Logs as follows:

Example JSON log record
{ "timestamp":"2023-11-01T00:21:51.358Z", "level":"DEBUG", "message":"This is a debug log", "AWSrequestId":"93f25699-2cbf-4976-8f94-336a0aa98c6f" }

If you don't assign a level to your log output, Lambda will automatically assign it the level INFO.

If your code already uses another logging library to produce JSON structured logs, you don’t need to make any changes. Lambda doesn’t double-encode any logs that are already JSON encoded. Even if you configure your function to use the JSON log format, your logging outputs appear in CloudWatch in the JSON structure you define.

Using log-level filtering with Java

For Amazon Lambda to filter your application logs according to their log level, your function must use JSON formatted logs. You can achieve this in two ways:

When you configure your function to use log-level filtering, you must select from the following options for the level of logs you want Lambda to send to CloudWatch Logs:

Log level Standard usage
TRACE (most detail) The most fine-grained information used to trace the path of your code's execution
DEBUG Detailed information for system debugging
INFO Messages that record the normal operation of your function
WARN Messages about potential errors that may lead to unexpected behavior if unaddressed
ERROR Messages about problems that prevent the code from performing as expected
FATAL (least detail) Messages about serious errors that cause the application to stop functioning

For Lambda to filter your function's logs, you must also include a "timestamp" key value pair in your JSON log output. The time must be specified in valid RFC 3339 timestamp format. If you don't supply a valid timestamp, Lambda will assign the log the level INFO and add a timestamp for you.

Lambda sends logs of the selected level and lower to CloudWatch. For example, if you configure a log level of WARN, Lambda will send logs corresponding to the WARN, ERROR, and FATAL levels.

Advanced logging with Log4j2 and SLF4J


Amazon Lambda does not include Log4j2 in its managed runtimes or base container images. These are therefore not affected by the issues described in CVE-2021-44228, CVE-2021-45046, and CVE-2021-45105.

For cases where a customer function includes an impacted Log4j2 version, we have applied a change to the Lambda Java managed runtimes and base container images that helps to mitigate the issues in CVE-2021-44228, CVE-2021-45046, and CVE-2021-45105. As a result of this change, customers using Log4J2 may see an additional log entry, similar to "Transforming org/apache/logging/log4j/core/lookup/JndiLookup (". Any log strings that reference the jndi mapper in the Log4J2 output will be replaced with "Patched JndiLookup::lookup()".

Independent of this change, we strongly encourage all customers whose functions include Log4j2 to update to the latest version. Specifically, customers using the aws-lambda-java-log4j2 library in their functions should update to version 1.5.0 (or later), and redeploy their functions. This version updates the underlying Log4j2 utility dependencies to version 2.17.0 (or later). The updated aws-lambda-java-log4j2 binary is available at the Maven repository and its source code is available in Github.

Lastly, take note that any libraries related to aws-lambda-java-log4j (v1.0.0 or 1.0.1) should not be used under any circumstance. These libraries are related to version 1.x of log4j which went end of life in 2015. The libraries are not supported, not maintained, not patched, and have known security vulnerabilities.

To customize log output, support logging during unit tests, and log Amazon SDK calls, use Apache Log4j2 with SLF4J. Log4j is a logging library for Java programs that enables you to configure log levels and use appender libraries. SLF4J is a facade library that lets you change which library you use without changing your function code.

To add the request ID to your function's logs, use the appender in the aws-lambda-java-log4j2 library.

Example src/main/resources/log4j2.xml – Appender configuration
<Configuration> <Appenders> <Lambda name="Lambda" format="${env:AWS_LAMBDA_LOG_FORMAT:-TEXT}"> <LambdaTextFormat> <PatternLayout> <pattern>%d{yyyy-MM-dd HH:mm:ss} %X{AWSRequestId} %-5p %c{1} - %m%n </pattern> </PatternLayout> </LambdaTextFormat> <LambdaJSONFormat> <JsonTemplateLayout eventTemplateUri="classpath:LambdaLayout.json" /> </LambdaJSONFormat> </Lambda> </Appenders> <Loggers> <Root level="${env:AWS_LAMBDA_LOG_LEVEL:-INFO}"> <AppenderRef ref="Lambda"/> </Root> <Logger name="" level="WARN" /> <Logger name="" level="DEBUG" /> </Loggers> </Configuration>

You can decide how your Log4j2 logs are configured for either plain text or JSON outputs by specifying a layout under the <LambdaTextFormat> and <LambdaJSONFormat> tags.

In this example, in text mode, each line is prepended with the date, time, request ID, log level, and class name. In JSON mode, the <JsonTemplateLayout> is used with a configuration that ships together with the aws-lambda-java-log4j2 library.

SLF4J is a facade library for logging in Java code. In your function code, you use the SLF4J logger factory to retrieve a logger with methods for log levels like info() and warn(). In your build configuration, you include the logging library and SLF4J adapter in the classpath. By changing the libraries in the build configuration, you can change the logger type without changing your function code. SLF4J is required to capture logs from the SDK for Java.

In the following example code, the handler class uses SLF4J to retrieve a logger.

Example src/main/java/example/ – Logging with SLF4J
package example; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import; import; import; import static org.apache.logging.log4j.CloseableThreadContext.put; public class HandlerS3 implements RequestHandler<S3Event, String>{ private static final Logger logger = LoggerFactory.getLogger(HandlerS3.class); @Override public String handleRequest(S3Event event, Context context) { for(var record : event.getRecords()) { try (var loggingCtx = put("awsRegion", record.getAwsRegion())) { loggingCtx.put("eventName", record.getEventName()); loggingCtx.put("bucket", record.getS3().getBucket().getName()); loggingCtx.put("key", record.getS3().getObject().getKey());"Handling s3 event"); } } return "Ok"; } }

This code produces log outputs like the following:

Example log format
{ "timestamp": "2023-11-15T16:56:00.815Z", "level": "INFO", "message": "Handling s3 event", "logger": "example.HandlerS3", "AWSRequestId": "0bced576-3936-4e5a-9dcd-db9477b77f97", "awsRegion": "eu-south-1", "bucket": "java-logging-test-input-bucket", "eventName": "ObjectCreated:Put", "key": "test-folder/" }

The build configuration takes runtime dependencies on the Lambda appender and SLF4J adapter, and implementation dependencies on Log4j2.

Example build.gradle – Logging dependencies
dependencies { ... 'com.amazonaws:aws-lambda-java-log4j2:[1.6.0,)', 'com.amazonaws:aws-lambda-java-events:[3.11.3,)', 'org.apache.logging.log4j:log4j-layout-template-json:[2.17.1,)', 'org.apache.logging.log4j:log4j-slf4j2-impl:[2.19.0,)', ... }

When you run your code locally for tests, the context object with the Lambda logger is not available, and there's no request ID for the Lambda appender to use. For example test configurations, see the sample applications in the next section.

Other tools and libraries

Powertools for Amazon Lambda (Java) is a developer toolkit to implement Serverless best practices and increase developer velocity. The Logging utility provides a Lambda optimized logger which includes additional information about function context across all your functions with output structured as JSON. Use this utility to do the following:

  • Capture key fields from the Lambda context, cold start and structures logging output as JSON

  • Log Lambda invocation events when instructed (disabled by default)

  • Print all the logs only for a percentage of invocations via log sampling (disabled by default)

  • Append additional keys to structured log at any point in time

  • Use a custom log formatter (Bring Your Own Formatter) to output logs in a structure compatible with your organization’s Logging RFC

Using Powertools for Amazon Lambda (Java) and Amazon SAM for structured logging

Follow the steps below to download, build, and deploy a sample Hello World Java application with integrated Powertools for Amazon Lambda (Java)~ modules using the Amazon SAM. This application implements a basic API backend and uses Powertools for emitting logs, metrics, and traces. It consists of an Amazon API Gateway endpoint and a Lambda function. When you send a GET request to the API Gateway endpoint, the Lambda function invokes, sends logs and metrics using Embedded Metric Format to CloudWatch, and sends traces to Amazon X-Ray. The function returns a hello world message.


To complete the steps in this section, you must have the following:

Deploy a sample Amazon SAM application
  1. Initialize the application using the Hello World Java template.

    sam init --app-template hello-world-powertools-java --name sam-app --package-type Zip --runtime java11 --no-tracing
  2. Build the app.

    cd sam-app && sam build
  3. Deploy the app.

    sam deploy --guided
  4. Follow the on-screen prompts. To accept the default options provided in the interactive experience, press Enter.


    For HelloWorldFunction may not have authorization defined, Is this okay?, make sure to enter y.

  5. Get the URL of the deployed application:

    aws cloudformation describe-stacks --stack-name sam-app --query 'Stacks[0].Outputs[?OutputKey==`HelloWorldApi`].OutputValue' --output text
  6. Invoke the API endpoint:


    If successful, you'll see this response:

    {"message":"hello world"}
  7. To get the logs for the function, run sam logs. For more information, see Working with logs in the Amazon Serverless Application Model Developer Guide.

    sam logs --stack-name sam-app

    The log output looks like this:

    2023/02/03/[$LATEST]851411a899b545eea2cffeba4cfbec81 2023-02-03T09:24:34.095000 INIT_START Runtime Version: java:11.v15 Runtime Version ARN: arn:aws:lambda:eu-central-1::runtime:0a25e3e7a1cc9ce404bc435eeb2ad358d8fa64338e618d0c224fe509403583ca 2023/02/03/[$LATEST]851411a899b545eea2cffeba4cfbec81 2023-02-03T09:24:34.114000 Picked up JAVA_TOOL_OPTIONS: -XX:+TieredCompilation -XX:TieredStopAtLevel=1 2023/02/03/[$LATEST]851411a899b545eea2cffeba4cfbec81 2023-02-03T09:24:34.793000 Transforming org/apache/logging/log4j/core/lookup/JndiLookup (lambdainternal.CustomerClassLoader@1a6c5a9e) 2023/02/03/[$LATEST]851411a899b545eea2cffeba4cfbec81 2023-02-03T09:24:35.252000 START RequestId: 7fcf1548-d2d4-41cd-a9a8-6ae47c51f765 Version: $LATEST 2023/02/03/[$LATEST]851411a899b545eea2cffeba4cfbec81 2023-02-03T09:24:36.531000 { "_aws": { "Timestamp": 1675416276051, "CloudWatchMetrics": [ { "Namespace": "sam-app-powerools-java", "Metrics": [ { "Name": "ColdStart", "Unit": "Count" } ], "Dimensions": [ [ "Service", "FunctionName" ] ] } ] }, "function_request_id": "7fcf1548-d2d4-41cd-a9a8-6ae47c51f765", "traceId": "Root=1-63dcd2d1-25f90b9d1c753a783547f4dd;Parent=e29684c1be352ce4;Sampled=1", "FunctionName": "sam-app-HelloWorldFunction-y9Iu1FLJJBGD", "functionVersion": "$LATEST", "ColdStart": 1.0, "Service": "service_undefined", "logStreamId": "2023/02/03/[$LATEST]851411a899b545eea2cffeba4cfbec81", "executionEnvironment": "AWS_Lambda_java11" } 2023/02/03/[$LATEST]851411a899b545eea2cffeba4cfbec81 2023-02-03T09:24:36.974000 Feb 03, 2023 9:24:36 AM com.amazonaws.xray.AWSXRayRecorder <init> 2023/02/03/[$LATEST]851411a899b545eea2cffeba4cfbec81 2023-02-03T09:24:36.993000 Feb 03, 2023 9:24:36 AM com.amazonaws.xray.config.DaemonConfiguration <init> 2023/02/03/[$LATEST]851411a899b545eea2cffeba4cfbec81 2023-02-03T09:24:36.993000 INFO: Environment variable AWS_XRAY_DAEMON_ADDRESS is set. Emitting to daemon on address XXXX.XXXX.XXXX.XXXX:2000. 2023/02/03/[$LATEST]851411a899b545eea2cffeba4cfbec81 2023-02-03T09:24:37.331000 09:24:37.294 [main] INFO helloworld.App - {"version":null,"resource":"/hello","path":"/hello/","httpMethod":"GET","headers":{"Accept":"*/*","CloudFront-Forwarded-Proto":"https","CloudFront-Is-Desktop-Viewer":"true","CloudFront-Is-Mobile-Viewer":"false","CloudFront-Is-SmartTV-Viewer":"false","CloudFront-Is-Tablet-Viewer":"false","CloudFront-Viewer-ASN":"16509","CloudFront-Viewer-Country":"IE","Host":"","User-Agent":"curl/7.86.0","Via":"2.0 (CloudFront)","X-Amz-Cf-Id":"t9W5ByT11HaY33NM8YioKECn_4eMpNsOMPfEVRczD7T1RdhbtiwV1Q==","X-Amzn-Trace-Id":"Root=1-63dcd2d1-25f90b9d1c753a783547f4dd","X-Forwarded-For":"XX.XXX.XXX.XX, XX.XXX.XXX.XX","X-Forwarded-Port":"443","X-Forwarded-Proto":"https"},"multiValueHeaders":{"Accept":["*/*"],"CloudFront-Forwarded-Proto":["https"],"CloudFront-Is-Desktop-Viewer":["true"],"CloudFront-Is-Mobile-Viewer":["false"],"CloudFront-Is-SmartTV-Viewer":["false"],"CloudFront-Is-Tablet-Viewer":["false"],"CloudFront-Viewer-ASN":["16509"],"CloudFront-Viewer-Country":["IE"],"Host":[""],"User-Agent":["curl/7.86.0"],"Via":["2.0 (CloudFront)"],"X-Amz-Cf-Id":["t9W5ByT11HaY33NM8YioKECn_4eMpNsOMPfEVRczD7T1RdhbtiwV1Q=="],"X-Amzn-Trace-Id":["Root=1-63dcd2d1-25f90b9d1c753a783547f4dd"],"X-Forwarded-For":["XXX, XXX"],"X-Forwarded-Port":["443"],"X-Forwarded-Proto":["https"]},"queryStringParameters":null,"multiValueQueryStringParameters":null,"pathParameters":null,"stageVariables":null,"requestContext":{"accountId":"XXX","stage":"Prod","resourceId":"at73a1","requestId":"ba09ecd2-acf3-40f6-89af-fad32df67597","operationName":null,"identity":{"cognitoIdentityPoolId":null,"accountId":null,"cognitoIdentityId":null,"caller":null,"apiKey":null,"principalOrgId":null,"sourceIp":"","cognitoAuthenticationType":null,"cognitoAuthenticationProvider":null,"userArn":null,"userAgent":"curl/7.86.0","user":null,"accessKey":null},"resourcePath":"/hello","httpMethod":"GET","apiId":"XXX","path":"/Prod/hello/","authorizer":null},"body":null,"isBase64Encoded":false} 2023/02/03/[$LATEST]851411a899b545eea2cffeba4cfbec81 2023-02-03T09:24:37.351000 09:24:37.351 [main] INFO helloworld.App - Retrieving 2023/02/03/[$LATEST]851411a899b545eea2cffeba4cfbec81 2023-02-03T09:24:39.313000 { "function_request_id": "7fcf1548-d2d4-41cd-a9a8-6ae47c51f765", "traceId": "Root=1-63dcd2d1-25f90b9d1c753a783547f4dd;Parent=e29684c1be352ce4;Sampled=1", "xray_trace_id": "1-63dcd2d1-25f90b9d1c753a783547f4dd", "functionVersion": "$LATEST", "Service": "service_undefined", "logStreamId": "2023/02/03/[$LATEST]851411a899b545eea2cffeba4cfbec81", "executionEnvironment": "AWS_Lambda_java11" } 2023/02/03/[$LATEST]851411a899b545eea2cffeba4cfbec81 2023-02-03T09:24:39.371000 END RequestId: 7fcf1548-d2d4-41cd-a9a8-6ae47c51f765 2023/02/03/[$LATEST]851411a899b545eea2cffeba4cfbec81 2023-02-03T09:24:39.371000 REPORT RequestId: 7fcf1548-d2d4-41cd-a9a8-6ae47c51f765 Duration: 4118.98 ms Billed Duration: 4119 ms Memory Size: 512 MB Max Memory Used: 152 MB Init Duration: 1155.47 ms XRAY TraceId: 1-63dcd2d1-25f90b9d1c753a783547f4dd SegmentId: 3a028fee19b895cb Sampled: true
  8. This is a public API endpoint that is accessible over the internet. We recommend that you delete the endpoint after testing.

    sam delete

Managing log retention

Log groups aren't deleted automatically when you delete a function. To avoid storing logs indefinitely, delete the log group, or configure a retention period after which CloudWatch automatically deletes the logs. To set up log retention, add the following to your Amazon SAM template:

Resources: HelloWorldFunction: Type: AWS::Serverless::Function Properties: # Omitting other properties LogGroup: Type: AWS::Logs::LogGroup Properties: LogGroupName: !Sub "/aws/lambda/${HelloWorldFunction}" RetentionInDays: 7

Using the Lambda console

You can use the Lambda console to view log output after you invoke a Lambda function.

If your code can be tested from the embedded Code editor, you will find logs in the execution results. When you use the console test feature to invoke a function, you'll find Log output in the Details section.

Using the CloudWatch console

You can use the Amazon CloudWatch console to view logs for all Lambda function invocations.

To view logs on the CloudWatch console
  1. Open the Log groups page on the CloudWatch console.

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

  3. Choose a log stream.

Each log stream corresponds to an instance of your function. A log stream appears when you update your Lambda function, and when additional instances are created to handle multiple concurrent invocations. To find logs for a specific invocation, we recommend instrumenting your function with Amazon X-Ray. X-Ray records details about the request and the log stream in the trace.

Using the Amazon Command Line Interface (Amazon CLI)

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

You can use the Amazon 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 --cli-binary-format raw-in-base64-out | base64 --decode

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

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 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

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

#!/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
Example retrieve the last five log events

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


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" }

Deleting logs

Log groups aren't deleted automatically when you delete a function. To avoid storing logs indefinitely, delete the log group, or configure a retention period after which logs are deleted automatically.

Sample logging code

The GitHub repository for this guide includes sample applications that demonstrate the use of various logging configurations. Each sample application includes scripts for easy deployment and cleanup, an Amazon SAM template, and supporting resources.

Sample Lambda applications in Java
  • java17-examples – A Java function that demonstrates how to use a Java record to represent an input event data object.

  • java-basic – A collection of minimal Java functions with unit tests and variable logging configuration.

  • java-events – A collection of Java functions that contain skeleton code for how to handle events from various services such as Amazon API Gateway, Amazon SQS, and Amazon Kinesis. These functions use the latest version of the aws-lambda-java-events library (3.0.0 and newer). These examples do not require the Amazon SDK as a dependency.

  • s3-java – A Java function that processes notification events from Amazon S3 and uses the Java Class Library (JCL) to create thumbnails from uploaded image files.

  • Use API Gateway to invoke a Lambda function – A Java function that scans a Amazon DynamoDB table that contains employee information. It then uses Amazon Simple Notification Service to send a text message to employees celebrating their work anniversaries. This example uses API Gateway to invoke the function.

The java-basic sample application shows a minimal logging configuration that supports logging tests. The handler code uses the LambdaLogger logger provided by the context object. For tests, the application uses a custom TestLogger class that implements the LambdaLogger interface with a Log4j2 logger. It uses SLF4J as a facade for compatibility with the Amazon SDK. Logging libraries are excluded from build output to keep the deployment package small.