Is it possible to change the log level of an AWS Lambda at runtime?
Yes it's possible! You need to take care of two things:
- One, update your lambda environment variable
- Two, ensure that log4j will pick up the update
For the first problem, all you need to do is pass a lambda environment variable with name JAVA_TOOL_OPTIONS
and value "-DLOG_LEVEL=DEBUG"
.
For the second point, you can add this to your Java project src/main/resources/log4j.properties
with content something like
log4j.rootCategory=${LOG_LEVEL}, LAMBDA
LOG_LEVEL_PATTERN=%5p
LOG_PATTERN=[%d{yyyy-MM-dd HH:mm:ss.SSS}] boot%X{context} ${LOG_LEVEL_PATTERN} [%t] - %c{1}: %m%n
log4j.appender.LAMBDA=com.amazonaws.services.lambda.runtime.log4j.LambdaAppender
log4j.appender.LAMBDA.layout=org.apache.log4j.PatternLayout
log4j.appender.LAMBDA.layout.conversionPattern=${LOG_PATTERN}
And that's it!
If everything goes well you should soon see in your logs a line reading something like
Picked up JAVA_TOOL_OPTIONS: -DLOG_LEVEL=DEBUG
and hopefully start seeing some debug statements.
Notice how LOG_LEVEL
is embedded in the value of the lambda variable as opposed to being the variable name. This is a useful indirect way to feed JVM arguments down a lambda which you can then use as system properties.
Kudos to https://zenidas.wordpress.com/recipes/system-properties-for-a-java-lambda-function/
I was able to resolve this by using the amazon version of log4j2, and making a change to the log4j2.xml configuration file Add these dependencies to maven
<dependency>
<groupId>com.amazonaws</groupId>
<artifactId>aws-lambda-java-log4j2</artifactId>
<version>1.1.0</version>
</dependency>
<dependency>
<groupId>org.apache.logging.log4j</groupId>
<artifactId>log4j-core</artifactId>
<version>2.11.2</version>
</dependency>
<dependency>
<groupId>org.apache.logging.log4j</groupId>
<artifactId>log4j-api</artifactId>
<version>2.11.2</version>
</dependency>
use the environment variable in the level of the logger in the configuration
<?xml version="1.0" encoding="UTF-8"?>
<Configuration
packages="com.amazonaws.services.lambda.runtime.log4j2">
<Appenders>
<Lambda name="Lambda">
<PatternLayout>
<pattern>%d{yyyy-MM-dd HH:mm:ss} %X{AWSRequestId} %-5p %c{1}:%L - %m%n</pattern>
</PatternLayout>
</Lambda>
</Appenders>
<Loggers>
<Root level="${env:LOG_LEVEL}">
<AppenderRef ref="Lambda" />
</Root>
</Loggers>
</Configuration>
finally, use the log4j2 logger in the lambda itself
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
public class MyLambdaHandler implements RequestHandler<Void, Void> {
private static final Logger LOGGER = LogManager.getLogger(MyLambdaHandler .class);
public Void handleRequest(Void myVoid, Context context) {
LOGGER.error("Log info enabled: {}", LOGGER.isInfoEnabled());
LOGGER.info("Info messge");
LOGGER.error("Log error enabled: {}", LOGGER.isErrorEnabled());
LOGGER.error("Error Message");
LOGGER.error("Log trace enabled: {}", LOGGER.isTraceEnabled());
LOGGER.trace("trace message");
LOGGER.error("Log warning enabled: {}", LOGGER.isWarnEnabled());
LOGGER.warn("warn message");
LOGGER.error("Log debug enabled: {}", LOGGER.isDebugEnabled());
LOGGER.debug("debug message");
return null;
}
}
then set the LOG_LEVEL environment variable to the appropriate level to see the the relevant entries in the logs