title	description
Logging	Core utility

Logging provides an opinionated logger with output structured as JSON.

Key features

Capture key fields from Lambda context, cold start and structures logging output as JSON
Log Lambda event when instructed, disabled by default, can be enabled explicitly via annotation param
Append additional keys to structured log at any point in time

Install

Depending on your version of Java (either Java 1.8 or 11+), the configuration slightly changes.

=== "Maven Java 11+"

```xml hl_lines="3-7 16 18 24-27"
<dependencies>
    ...
    <dependency>
        <groupId>software.amazon.lambda</groupId>
        <artifactId>powertools-logging</artifactId>
        <version>{{ powertools.version }}</version>
    </dependency>
    ...
</dependencies>
...
<!-- configure the aspectj-maven-plugin to compile-time weave (CTW) the aws-lambda-powertools-java aspects into your project -->
<build>
    <plugins>
        ...
        <plugin>
             <groupId>dev.aspectj</groupId>
             <artifactId>aspectj-maven-plugin</artifactId>
             <version>1.13.1</version>
             <configuration>
                 <source>11</source> <!-- or higher -->
                 <target>11</target> <!-- or higher -->
                 <complianceLevel>11</complianceLevel> <!-- or higher -->
                 <aspectLibraries>
                     <aspectLibrary>
                         <groupId>software.amazon.lambda</groupId>
                         <artifactId>powertools-logging</artifactId>
                     </aspectLibrary>
                 </aspectLibraries>
             </configuration>
             <executions>
                 <execution>
                     <goals>
                         <goal>compile</goal>
                     </goals>
                 </execution>
             </executions>
        </plugin>
        ...
    </plugins>
</build>
```

=== "Maven Java 1.8"

```xml hl_lines="3-7 16 18 24-27"
<dependencies>
    ...
    <dependency>
        <groupId>software.amazon.lambda</groupId>
        <artifactId>powertools-logging</artifactId>
        <version>{{ powertools.version }}</version>
    </dependency>
    ...
</dependencies>
...
<!-- configure the aspectj-maven-plugin to compile-time weave (CTW) the aws-lambda-powertools-java aspects into your project -->
<build>
    <plugins>
        ...
        <plugin>
             <groupId>org.codehaus.mojo</groupId>
             <artifactId>aspectj-maven-plugin</artifactId>
             <version>1.14.0</version>
             <configuration>
                 <source>1.8</source>
                 <target>1.8</target>
                 <complianceLevel>1.8</complianceLevel>
                 <aspectLibraries>
                     <aspectLibrary>
                         <groupId>software.amazon.lambda</groupId>
                         <artifactId>powertools-logging</artifactId>
                     </aspectLibrary>
                 </aspectLibraries>
             </configuration>
             <executions>
                 <execution>
                     <goals>
                         <goal>compile</goal>
                     </goals>
                 </execution>
             </executions>
        </plugin>
        ...
    </plugins>
</build>
```

=== "Gradle Java 11+"

```groovy hl_lines="3 11"
    plugins {
        id 'java'
        id 'io.freefair.aspectj.post-compile-weaving' version '8.1.0'
    }
    
    repositories {
        mavenCentral()
    }
    
    dependencies {
        aspect 'software.amazon.lambda:powertools-logging:{{ powertools.version }}'
    }
    
    sourceCompatibility = 11
    targetCompatibility = 11
```

=== "Gradle Java 1.8"

```groovy hl_lines="3 11"
    plugins {
        id 'java'
        id 'io.freefair.aspectj.post-compile-weaving' version '6.6.3'
    }
    
    repositories {
        mavenCentral()
    }
    
    dependencies {
        aspect 'software.amazon.lambda:powertools-logging:{{ powertools.version }}'
    }
    
    sourceCompatibility = 1.8
    targetCompatibility = 1.8
```

Initialization

Powertools for AWS Lambda (Java) extends the functionality of Log4J. Below is an example #!xml log4j2.xml file, with the JsonTemplateLayout using #!json LambdaJsonLayout.json configured.

!!! info "LambdaJsonLayout is now deprecated"

Configuring utiltiy using `<LambdaJsonLayout/>` plugin is deprecated now. While utility still supports the old configuration, we strongly recommend upgrading the 
`log4j2.xml` configuration to `JsonTemplateLayout` instead. [JsonTemplateLayout](https://logging.apache.org/log4j/2.x/manual/json-template-layout.html) is recommended way of doing structured logging.

Please follow [this guide](#upgrade-to-jsontemplatelayout-from-deprecated-lambdajsonlayout-configuration-in-log4j2xml) for upgrade steps.

=== "log4j2.xml"

```xml hl_lines="5"
<?xml version="1.0" encoding="UTF-8"?>
<Configuration>
    <Appenders>
        <Console name="JsonAppender" target="SYSTEM_OUT">
            <JsonTemplateLayout eventTemplateUri="classpath:LambdaJsonLayout.json" />
        </Console>
    </Appenders>
    <Loggers>
        <Logger name="JsonLogger" level="INFO" additivity="false">
            <AppenderRef ref="JsonAppender"/>
        </Logger>
        <Root level="info">
            <AppenderRef ref="JsonAppender"/>
        </Root>
    </Loggers>
</Configuration>
```

You can also override log level by setting POWERTOOLS_LOG_LEVEL env var. Here is an example using AWS Serverless Application Model (SAM)

=== "template.yaml" yaml hl_lines="9 10" Resources: HelloWorldFunction: Type: AWS::Serverless::Function Properties: ... Runtime: java8 Environment: Variables: POWERTOOLS_LOG_LEVEL: DEBUG POWERTOOLS_SERVICE_NAME: example

You can also explicitly set a service name via POWERTOOLS_SERVICE_NAME env var. This sets service key that will be present across all log statements.

Standard structured keys

Your logs will always include the following keys to your structured logging:

Key	Type	Example	Description
timestamp	String	"2020-05-24 18:17:33,774"	Timestamp of actual log statement
level	String	"INFO"	Logging level
coldStart	Boolean	true	ColdStart value.
service	String	"payment"	Service name defined. "service_undefined" will be used if unknown
samplingRate	int	0.1	Debug logging sampling rate in percentage e.g. 10% in this case
message	String	"Collecting payment"	Log statement value. Unserializable JSON values will be casted to string
functionName	String	"example-powertools-HelloWorldFunction-1P1Z6B39FLU73"
functionVersion	String	"12"
functionMemorySize	String	"128"
functionArn	String	"arn:aws:lambda:eu-west-1:012345678910:function:example-powertools-HelloWorldFunction-1P1Z6B39FLU73"
xray_trace_id	String	"1-5759e988-bd862e3fe1be46a994272793"	X-Ray Trace ID when Lambda function has enabled Tracing
function_request_id	String	"899856cb-83d1-40d7-8611-9e78f15f32f4""	AWS Request ID from lambda context

Capturing context Lambda info

When debugging in non-production environments, you can instruct Logger to log the incoming event with @Logger(logEvent = true) or via POWERTOOLS_LOGGER_LOG_EVENT=true environment variable.

!!! warning Log event is disabled by default to prevent sensitive info being logged.

=== "App.java"

```java hl_lines="14"
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import software.amazon.lambda.powertools.logging.LoggingUtils;
import software.amazon.lambda.powertools.logging.Logging;
...

/**
 * Handler for requests to Lambda function.
 */
public class App implements RequestHandler<APIGatewayProxyRequestEvent, APIGatewayProxyResponseEvent> {

    Logger log = LogManager.getLogger(App.class);

    @Logging
    public APIGatewayProxyResponseEvent handleRequest(final APIGatewayProxyRequestEvent input, final Context context) {
     ...
    }
}
```

=== "AppLogEvent.java"

```java hl_lines="8"
/**
 * Handler for requests to Lambda function.
 */
public class AppLogEvent implements RequestHandler<APIGatewayProxyRequestEvent, APIGatewayProxyResponseEvent> {

    Logger log = LogManager.getLogger(AppLogEvent.class);
    
    @Logging(logEvent = true)
    public APIGatewayProxyResponseEvent handleRequest(final APIGatewayProxyRequestEvent input, final Context context) {
     ...
    }
}
```

Customising fields in logs

Utility by default emits timestamp field in the logs in format yyyy-MM-dd'T'HH:mm:ss.SSSZz and in system default timezone. If you need to customize format and timezone, you can do so by configuring log4j2.component.properties and configuring properties as shown in example below:

=== "log4j2.component.properties"

```properties hl_lines="1 2"
log4j.layout.jsonTemplate.timestampFormatPattern=yyyy-MM-dd'T'HH:mm:ss.SSSZz
log4j.layout.jsonTemplate.timeZone=Europe/Oslo
```

Utility also provides sample template for Elastic Common Schema(ECS) layout. The field emitted in logs will follow specs from ECS together with field captured by utility as mentioned above.

Use LambdaEcsLayout.json as eventTemplateUri when configuring JsonTemplateLayout.

=== "log4j2.xml"

```xml hl_lines="5"
<?xml version="1.0" encoding="UTF-8"?>
<Configuration>
    <Appenders>
        <Console name="JsonAppender" target="SYSTEM_OUT">
            <JsonTemplateLayout eventTemplateUri="classpath:LambdaEcsLayout.json" />
        </Console>
    </Appenders>
    <Loggers>
        <Logger name="JsonLogger" level="INFO" additivity="false">
            <AppenderRef ref="JsonAppender"/>
        </Logger>
        <Root level="info">
            <AppenderRef ref="JsonAppender"/>
        </Root>
    </Loggers>
</Configuration>
```

Setting a Correlation ID

You can set a Correlation ID using correlationIdPath attribute by passing a JSON Pointer expression{target="_blank"}.

=== "App.java"

```java hl_lines="8"
/**
 * Handler for requests to Lambda function.
 */
public class App implements RequestHandler<APIGatewayProxyRequestEvent, APIGatewayProxyResponseEvent> {

    Logger log = LogManager.getLogger(App.class);

    @Logging(correlationIdPath = "/headers/my_request_id_header")
    public APIGatewayProxyResponseEvent handleRequest(final APIGatewayProxyRequestEvent input, final Context context) {
        ...
        log.info("Collecting payment")
        ...
    }
}
```

=== "Example Event"

```json hl_lines="3"
{
  "headers": {
	"my_request_id_header": "correlation_id_value"
  }
}
```

=== "Example CloudWatch Logs excerpt"

```json hl_lines="11"
{
	"level": "INFO",
  	"message": "Collecting payment",
	"timestamp": "2021-05-03 11:47:12,494+0200",
  	"service": "payment",
  	"coldStart": true,
  	"functionName": "test",
  	"functionMemorySize": 128,
  	"functionArn": "arn:aws:lambda:eu-west-1:12345678910:function:test",
  	"function_request_id": "52fdfc07-2182-154f-163f-5f0f9a621d72",
  	"correlation_id": "correlation_id_value"
}
```

We provide built-in JSON Pointer expression{target="_blank"} for known event sources, where either a request ID or X-Ray Trace ID are present.

=== "App.java"

```java hl_lines="10"
import software.amazon.lambda.powertools.logging.CorrelationIdPathConstants;

/**
 * Handler for requests to Lambda function.
 */
public class App implements RequestHandler<APIGatewayProxyRequestEvent, APIGatewayProxyResponseEvent> {

    Logger log = LogManager.getLogger(App.class);

    @Logging(correlationIdPath = CorrelationIdPathConstants.API_GATEWAY_REST)
    public APIGatewayProxyResponseEvent handleRequest(final APIGatewayProxyRequestEvent input, final Context context) {
        ...
        log.info("Collecting payment")
        ...
    }
}
```

=== "Example Event"

```json hl_lines="3"
{
  "requestContext": {
	"requestId": "correlation_id_value"
  }
}
```

=== "Example CloudWatch Logs excerpt"

```json hl_lines="11"
{
	"level": "INFO",
  	"message": "Collecting payment",
	"timestamp": "2021-05-03 11:47:12,494+0200",
  	"service": "payment",
  	"coldStart": true,
  	"functionName": "test",
  	"functionMemorySize": 128,
  	"functionArn": "arn:aws:lambda:eu-west-1:12345678910:function:test",
  	"function_request_id": "52fdfc07-2182-154f-163f-5f0f9a621d72",
  	"correlation_id": "correlation_id_value"
}
```

Appending additional keys

!!! info "Custom keys are persisted across warm invocations" Always set additional keys as part of your handler to ensure they have the latest value, or explicitly clear them with clearState=true.

You can append your own keys to your existing logs via appendKey.

=== "App.java"

```java hl_lines="11 19"
/**
 * Handler for requests to Lambda function.
 */
public class App implements RequestHandler<APIGatewayProxyRequestEvent, APIGatewayProxyResponseEvent> {

    Logger log = LogManager.getLogger(App.class);

    @Logging(logEvent = true)
    public APIGatewayProxyResponseEvent handleRequest(final APIGatewayProxyRequestEvent input, final Context context) {
        ...
        LoggingUtils.appendKey("test", "willBeLogged");
        ...

        ...
         Map<String, String> customKeys = new HashMap<>();
         customKeys.put("test", "value");
         customKeys.put("test1", "value1");

         LoggingUtils.appendKeys(customKeys);
        ...
    }
}
```

Removing additional keys

You can remove any additional key from entry using LoggingUtils.removeKeys().

=== "App.java"

```java hl_lines="19 20"
/**
 * Handler for requests to Lambda function.
 */
public class App implements RequestHandler<APIGatewayProxyRequestEvent, APIGatewayProxyResponseEvent> {

    Logger log = LogManager.getLogger(App.class);

    @Logging(logEvent = true)
    public APIGatewayProxyResponseEvent handleRequest(final APIGatewayProxyRequestEvent input, final Context context) {
        ...
        LoggingUtils.appendKey("test", "willBeLogged");
        ...
        Map<String, String> customKeys = new HashMap<>();
        customKeys.put("test1", "value");
        customKeys.put("test2", "value1");

        LoggingUtils.appendKeys(customKeys);
        ...
        LoggingUtils.removeKey("test");
        LoggingUtils.removeKeys("test1", "test2");
        ...
    }
}
```

Clearing all state

Logger is commonly initialized in the global scope. Due to Lambda Execution Context reuse, this means that custom keys can be persisted across invocations. If you want all custom keys to be deleted, you can use clearState=true attribute on @Logging annotation.

=== "App.java"

```java hl_lines="8 12"
/**
 * Handler for requests to Lambda function.
 */
public class App implements RequestHandler<APIGatewayProxyRequestEvent, APIGatewayProxyResponseEvent> {

    Logger log = LogManager.getLogger(App.class);

    @Logging(clearState = true)
    public APIGatewayProxyResponseEvent handleRequest(final APIGatewayProxyRequestEvent input, final Context context) {
        ...
        if(input.getHeaders().get("someSpecialHeader")) {
            LoggingUtils.appendKey("specialKey", "value");
        }
        
        log.info("Collecting payment");
        ...
    }
}
```

=== "#1 Request"

```json hl_lines="11"
{
	"level": "INFO",
  	"message": "Collecting payment",
	"timestamp": "2021-05-03 11:47:12,494+0200",
  	"service": "payment",
  	"coldStart": true,
  	"functionName": "test",
  	"functionMemorySize": 128,
  	"functionArn": "arn:aws:lambda:eu-west-1:12345678910:function:test",
  	"function_request_id": "52fdfc07-2182-154f-163f-5f0f9a621d72",
    "specialKey": "value"
}
```

=== "#2 Request"

```json
{
	"level": "INFO",
  	"message": "Collecting payment",
	"timestamp": "2021-05-03 11:47:12,494+0200",
  	"service": "payment",
  	"coldStart": true,
  	"functionName": "test",
  	"functionMemorySize": 128,
  	"functionArn": "arn:aws:lambda:eu-west-1:12345678910:function:test",
  	"function_request_id": "52fdfc07-2182-154f-163f-5f0f9a621d72"
}
```

Override default object mapper

You can optionally choose to override default object mapper which is used to serialize lambda function events. You might want to supply custom object mapper in order to control how serialisation is done, for example, when you want to log only specific fields from received event due to security.

=== "App.java"

```java hl_lines="9 10"
/**
 * Handler for requests to Lambda function.
 */
public class App implements RequestHandler<APIGatewayProxyRequestEvent, APIGatewayProxyResponseEvent> {

    Logger log = LogManager.getLogger(App.class);

    static {
        ObjectMapper objectMapper = new ObjectMapper();
        LoggingUtils.defaultObjectMapper(objectMapper);
    }

    @Logging(logEvent = true)
    public APIGatewayProxyResponseEvent handleRequest(final APIGatewayProxyRequestEvent input, final Context context) {
        ...
    }
}
```

Sampling debug logs

You can dynamically set a percentage of your logs to DEBUG level via env var POWERTOOLS_LOGGER_SAMPLE_RATE or via samplingRate attribute on annotation.

!!! info Configuration on environment variable is given precedence over sampling rate configuration on annotation, provided it's in valid value range.

=== "Sampling via annotation attribute"

```java hl_lines="8"
/**
 * Handler for requests to Lambda function.
 */
public class App implements RequestHandler<APIGatewayProxyRequestEvent, APIGatewayProxyResponseEvent> {

    Logger log = LogManager.getLogger(App.class);

    @Logging(samplingRate = 0.5)
    public APIGatewayProxyResponseEvent handleRequest(final APIGatewayProxyRequestEvent input, final Context context) {
     ...
    }
}
```

=== "Sampling via environment variable"

```yaml hl_lines="9"
Resources:
    HelloWorldFunction:
        Type: AWS::Serverless::Function
        Properties:
        ...
        Runtime: java8
        Environment:
            Variables:
                POWERTOOLS_LOGGER_SAMPLE_RATE: 0.5
```

Upgrade to JsonTemplateLayout from deprecated LambdaJsonLayout configuration in log4j2.xml

Prior to version 1.10.0, only supported way of configuring log4j2.xml was via <LambdaJsonLayout/>. This plugin is deprecated now and will be removed in future version. Switching to JsonTemplateLayout is straight forward.

Below examples shows deprecated and new configuration of log4j2.xml.

=== "Deprecated configuration of log4j2.xml"

```xml hl_lines="5"
<?xml version="1.0" encoding="UTF-8"?>
<Configuration>
    <Appenders>
        <Console name="JsonAppender" target="SYSTEM_OUT">
            <LambdaJsonLayout compact="true" eventEol="true"/>
        </Console>
    </Appenders>
    <Loggers>
        <Logger name="JsonLogger" level="INFO" additivity="false">
            <AppenderRef ref="JsonAppender"/>
        </Logger>
        <Root level="info">
            <AppenderRef ref="JsonAppender"/>
        </Root>
    </Loggers>
</Configuration>
```

=== "New configuration of log4j2.xml"

```xml hl_lines="5"
<?xml version="1.0" encoding="UTF-8"?>
<Configuration>
    <Appenders>
        <Console name="JsonAppender" target="SYSTEM_OUT">
            <JsonTemplateLayout eventTemplateUri="classpath:LambdaJsonLayout.json" />
        </Console>
    </Appenders>
    <Loggers>
        <Logger name="JsonLogger" level="INFO" additivity="false">
            <AppenderRef ref="JsonAppender"/>
        </Logger>
        <Root level="info">
            <AppenderRef ref="JsonAppender"/>
        </Root>
    </Loggers>
</Configuration>
```

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logging.md

logging.md

Install

Initialization

Standard structured keys

Capturing context Lambda info

Customising fields in logs

Setting a Correlation ID

Appending additional keys

Removing additional keys

Clearing all state

Override default object mapper

Sampling debug logs

Upgrade to JsonTemplateLayout from deprecated LambdaJsonLayout configuration in log4j2.xml

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logging.md

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logging.md

File metadata and controls

Install

Initialization

Standard structured keys

Capturing context Lambda info

Customising fields in logs

Setting a Correlation ID

Appending additional keys

Removing additional keys

Clearing all state

Override default object mapper

Sampling debug logs

Upgrade to JsonTemplateLayout from deprecated LambdaJsonLayout configuration in log4j2.xml