Bug: LogFormatter not forwarded to child loggers

[ghdoergeloh]

Use case

I found out, that I need to pass the LogFormatter to every child. It would be nice to forward the parents LogFormatter as the default to a child logger (via createChild) if no other LogFormatter was provided in that method.

Solution/User Experience

So if logger.createChild({}) is called without logFormatter it could just get the same instance, the parent is using.

Alternative solutions

No response

Acknowledgment

• This feature request meets Lambda Powertools Tenets
• Should this be considered in other Lambda Powertools languages? i.e. Python, Java

[shdq]

Hello @ghdoergeloh, thank you for opening the issue.

I think it is a bug since the child should have all the parent's attributes, except you overwrite them with options in createChild.

I made a quick fix, but I want to revisit other attributes that may be also missed for children. Then I open a PR.

@dreamorosi assign me, please. This is also part of #483.

[saragerion]

While I see the validity of the arguments presented, I'd like us to evaluate first if this would be a breaking change and the potential impact for developers by changing this behaviour now in their production environments. Let us look into it first.

[shdq]

@saragerion sure! For context, we changed the implementation of child logger in #1178 last year

[dreamorosi]

So, I have been thinking about this and after reading the documentation & docstrings of the method (createChild), I think this is a bug.

On a high level, and without context, when we create a child logger we want to create a new instance of this logger that is exactly the same as its parent, except for any override that is explicitly set during creation.

The docstring for the method reads this (emphasis mine):

It creates a separate Logger instance, identical to the current one. It's possible to overwrite the new instance options by passing them.

The docs instead, state this (emphasis mine):

Logger supports quick instance cloning via the createChild method

The wording of both pieces of documentation suggests that the parent and child should be exactly the same, except for any explicit override.

With the above in mind, I would expect the LogFormatter in children to be the same as the parent and I think it's safe to consider this a bug and not a breaking change as there's no wording nor indication that the formatter nor any other setting/option should not be persisted.

I do see however an opportunity to further flash out the wording in the docs to make it extra clear that all attributes and settings are forwarded - as identical might not be enough.