Lua script does not alter record

[dominikhei]

Hello, I have the following Filter, that should add a few keys to my json record:

    [FILTER]
        Name Lua
        Match *
        call add_datetime_fields
        code function add_datetime_fields(tag, timestamp, record) new_record = record new_record["year"] = record["date"]:sub(1, 4) new_record["month"] = record["date"]:sub(6, 7) new_record["day"] = record["date"]:sub(9, 10) new_record["time"] = record["date"]:sub(12, 13) return 2, timestamp, new_record end

However the logs that are output by fluentbit still look like this:

{"date":"2024-03-21T11:23:04.671154Z","log": "..."}

The new keys are not present, does anybody see what I did wrong?

[patrick-stephens]

It's hard to debug a single line LUA filter, does it work with https://fluent.github.io/lua-sandbox/?

[patrick-stephens]

Sounds like your LUA code is problematic then.
Make sure to update the sandbox input data and call your function cb_filter.
I would split out the usage of string extraction into separate local variables as well.

[dominikhei]

If I rename the function accordingly, everything works in the lua sandbox

[patrick-stephens]

OK, well that runs Fluent Bit underneath so sounds like it inherently works. My guess then is something else is wrong with your full config.

[dominikhei]

Alright @patrick-stephens then I will try to change some configs. Thanks for pointing out the Lua-sandbox, that is helpful for testing.

Quick question, can I somehow use the tag from the input inside a Lua filter?

[patrick-stephens]

Sure, it's part of the function signature...