How does AWS App Runner decide which logs to persist to CloudWatch?

Question

I searched the App runner config for the application but with no luck. I also read the docs here https://docs.aws.amazon.com/apprunner/latest/dg/monitor-cwl.html, but I can't seem to find the answer.

Our application has a mix of debug/info/error logs in this format:

```
{"level":"info","caller":"app/main.go:61","msg":"connecting to postgres database","version":""}
```

It seems that certain error logs of "level" : "error" are persisted to CloudWatch. However, not all of them are for some reason, and I don't know why.

For example I added this logline which triggers whenever any of our Handlers generate a 5xx

```
{"level":"error","caller":"api/routes.go:28","msg":"incoming request","version":"","uri":"/api/v1/users/profile","status":500,"method":"PUT","duration":"512ms","stacktrace":""}
```

But this never persists in CloudWatch for some reason

Accepted Answer

Hello.

I think the AppRunner logs that are output to standard output (/dev/stdout) and error output (/dev/stderr) are output to CloudWatch Logs.  
In other words, I don't know what kind of container you are running, but there may be logs that are not being output to standard output.  
I think it's a good idea to run the container locally and check that the logs are output to standard output.

How does AWS App Runner decide which logs to persist to CloudWatch?

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