Lambda now supports advanced logging configurations that allow CloudWatch logs to only ingest logs of a certain level based on the level attribute in a JSON-structured log payload.
This doesn't work with aws-lambda-go because improperly-shaped logs are automatically assigned to the INFO level.
make build
sam deploy --guided
The defaults for SAM setup should be fine. This will set both system an application log levels to INFO.
Invoke the Lambda function (it will error, that's intended) in the stack, then open the CloudWatch Logs for the function. There will be a number of log entries, but there are two that are important:
{
"time": "2023-11-17T18:52:05.505403525Z",
"level": "INFO",
"msg": "{\"errorMessage\":\"runtime error: index out of range [1] with length 1\",\"errorType\":\"boundsError\",\"stackTrace\":[{\"path\":\"github.com/aws/aws-lambda-go@v1.41.0/lambda/errors.go\",\"line\":39,\"label\":\"lambdaPanicResponse\"},{\"path\":\"github.com/aws/aws-lambda-go@v1.41.0/lambda/invoke_loop.go\",\"line\":116,\"label\":\"callBytesHandlerFunc.func1\"},{\"path\":\"runtime/panic.go\",\"line\":914,\"label\":\"gopanic\"},{\"path\":\"runtime/panic.go\",\"line\":114,\"label\":\"goPanicIndex\"},{\"path\":\"logme/main.go\",\"line\":24,\"label\":\"handler\"},{\"path\":\"logme/main.go\",\"line\":49,\"label\":\"handlerWithLambdaLogging[...].func1\"},{\"path\":\"reflect/value.go\",\"line\":596,\"label\":\"Value.call\"},{\"path\":\"reflect/value.go\",\"line\":380,\"label\":\"Value.Call\"},{\"path\":\"github.com/aws/aws-lambda-go@v1.41.0/lambda/handler.go\",\"line\":293,\"label\":\"reflectHandler.func2\"},{\"path\":\"github.com/aws/aws-lambda-go@v1.41.0/lambda/invoke_loop.go\",\"line\":119,\"label\":\"callBytesHandlerFunc\"},{\"path\":\"github.com/aws/aws-lambda-go@v1.41.0/lambda/invoke_loop.go\",\"line\":75,\"label\":\"handleInvoke\"},{\"path\":\"github.com/aws/aws-lambda-go@v1.41.0/lambda/invoke_loop.go\",\"line\":39,\"label\":\"startRuntimeAPILoop\"},{\"path\":\"github.com/aws/aws-lambda-go@v1.41.0/lambda/entry.go\",\"line\":106,\"label\":\"start\"},{\"path\":\"github.com/aws/aws-lambda-go@v1.41.0/lambda/entry_generic.go\",\"line\":20,\"label\":\"StartHandlerFunc[...]\"},{\"path\":\"logme/main.go\",\"line\":14,\"label\":\"main\"},{\"path\":\"runtime/proc.go\",\"line\":267,\"label\":\"main\"},{\"path\":\"runtime/asm_arm64.s\",\"line\":1197,\"label\":\"goexit\"}]}",
"requestId": "122704c2-24e7-4cdd-860d-27388e00f396"
}and
{
"time": "2023-11-17T18:52:05.506301428Z",
"level": "INFO",
"msg": "calling the handler function resulted in a panic, the process should exit",
"requestId": "122704c2-24e7-4cdd-860d-27388e00f396"
}Notice these are INFO-level. This is because aws-lambda-go doesn't structure the logs and Lambda automatically shapes unstructured logs this way if it's unspecified.
If you switch ApplicationLogLevelParameter to ERROR in the CloudFormation stack and update it and re-run the function, the error log entries will be omitted (because they're INFO-level).