Logging in AWS Lambda with slf4j

Yes, you can. Just add the following dependencies to your project:

    <dependency>
        <groupId>org.slf4j</groupId>
        <artifactId>jcl-over-slf4j</artifactId>
        <version>1.7.25</version>
    </dependency>
    <dependency>
        <groupId>org.slf4j</groupId>
        <artifactId>slf4j-log4j12</artifactId>
        <version>1.7.25</version>
    </dependency>
    <dependency>
        <groupId>com.amazonaws</groupId>
        <artifactId>aws-lambda-java-log4j</artifactId>
        <version>1.0.0</version>
    </dependency>

and create correct log4j.properties in /src/main/resources/ of your project, e.g.

log = .
log4j.rootLogger = DEBUG, LAMBDA

# Define the LAMBDA appender
log4j.appender.LAMBDA=com.amazonaws.services.lambda.runtime.log4j.LambdaAppender
log4j.appender.LAMBDA.layout=org.apache.log4j.PatternLayout
log4j.appender.LAMBDA.layout.conversionPattern=%d{yyyy-MM-dd HH:mm:ss} <%X{AWSRequestId}> %-5p %c{1}:%m%n

Just include following dependency:

<dependency>
    <groupId>io.symphonia</groupId>
    <artifactId>lambda-logging</artifactId>
    <version>1.0.0</version>
</dependency>

Source of lambda-logging code available at https://github.com/symphoniacloud/lambda-monitoring/tree/master/lambda-logging.

Background information available at: https://blog.symphonia.io/a-love-letter-to-lambda-logging-974b0eb49273

Ever since the AWS guide has been updated with details on Log4j 2 and SLF4J integration.

pom.xml:

<dependency>
    <groupId>com.amazonaws</groupId>
    <artifactId>aws-lambda-java-log4j2</artifactId>
    <version>1.5.1</version>
    <scope>runtime</scope>
</dependency>
<dependency>
    <groupId>org.apache.logging.log4j</groupId>
    <artifactId>log4j-slf4j18-impl</artifactId>
    <version>2.17.1</version>
</dependency>

And src/main/resources/log4j2.xml:

<Configuration status="WARN">
    <Appenders>
        <Lambda name="Lambda">
            <PatternLayout>
                <pattern>%d{yyyy-MM-dd HH:mm:ss} %X{AWSRequestId} %-5p %c{1} - %m%n</pattern>
            </PatternLayout>
        </Lambda>
    </Appenders>
    <Loggers>
        <Root level="INFO">
            <AppenderRef ref="Lambda"/>
        </Root>
        <Logger name="software.amazon.awssdk" level="WARN"/>
        <Logger name="software.amazon.awssdk.request" level="DEBUG"/>
    </Loggers>
</Configuration>

The jlib AWS Lambda Logback Appender allows you to use SLF4J with Logback from your AWS Lambda functions.

Simply add these dependencies:

Gradle (build.gradle)

dependencies {
    implementation 'org.slf4j:slf4j-api:1.8.0-beta2'
    runtimeOnly 'org.jlib:jlib-awslambda-logback:1.0.0'
}

Maven (pom.xml)

<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-api</artifactId>
    <version>1.8.0-beta2</version>
</dependency>
<dependency>
    <groupId>org.jlib</groupId>
    <artifactId>jlib-awslambda-logback</artifactId>
    <version>1.0.0</version>
    <scope>runtime</scope>
</dependency>

Then use the AwsLambdaAppender in your logging configuration:

Example XML configuration (src/main/resources/logback.xml)

<configuration>

    <appender name="awslambda" class="org.jlib.cloud.aws.lambda.logback.AwsLambdaAppender">
        <encoder type="ch.qos.logback.classic.encoder.PatternLayoutEncoder">
            <pattern>[%d{yyyy-MM-dd HH:mm:ss.SSS}] &lt;%-36X{AWSRequestId:-request-id-not-set-by-lambda-runtime}&gt;
%-5level %logger{10} - %msg%n</pattern>
        </encoder>
    </appender>

    <root level="INFO">
        <appender-ref ref="awslambda" />
    </root>

</configuration>

Unlike other solutions, this Logback Appender correctly handles multi-line log messages, especially stack traces, and produces only a single CloudWatch Logs event per message.

The library also allows you to include the AWSRequestId, provided by the AWS Lambda runtime, in every single log message for better tracing.

While log4j2 requires additional handling in the build when you create an uber-jar, this solution works out of the box.

Disclaimer: I'm the developer of jlib