Logger doesn't write to stdout/stderr by default resulting invalid JSON log entries in CloudWatch

[klindklind]

This is a Bug Report

Description

We switched from Winston to use your logger because it has many features we need out of the box. But then we realized that the loggings are not pure JSON anymore.

• What went wrong?
  Logs ingested into CloudWatch from our lambda which uses power-logger are not pure JSON. There is a row of plaintext metadata at the beginning of each log entry.

Implementation:

import log from '@dazn/lambda-powertools-logger'

log.info('foo', { bar: 'jar' })

will result in CloudWatch log like:

2020-12-03T09:59:57.754Z	4220ab3e-0559-4a5f-a318-d7b33be19925	INFO	
{
    "message": "foo",
    "data": {
        "bar": "jar"
    },
    "awsRegion": "eu-west-1",
    "functionName": "my-function",
    "functionVersion": "$LATEST",
    "functionMemorySize": "192",
     ... etc. metadata
}

• What did you expect should have happened?
  Only JSON

{
    "message": "foo",
    "data": {
        "bar": "jar"
    },
    "awsRegion": "eu-west-1",
    "functionName": "my-function",
    "functionVersion": "$LATEST",
    "functionMemorySize": "192",
     ... etc. metadata
}

should've been logged into CloudWatch.

• Workaround
  We forked the lambda-powertools-logger to explicitly log into process.stdout/.stderr. Could probably open a PR if your intention is to log pure JSON?

Additional Data

• Which powertool package are you using?: lambda-powertools-logger
• Which version are you using?: lambda-powertools-logger: 1.24.1
• Middy engine version you're using: 1.4.0
• Operating System: Lambda runtime Node 12.x