[ottl] ParseSeverity function

[djaglowski]

Component(s)

pkg/ottl

Is your feature request related to a problem? Please describe.

OTTL can directly set severity number and text, but it would be nice if there was an optimized function for interpreting values. Stanza currently has a dedicated severity interpreter which has a couple advantages over using OTTL:

1. Configuration is simple. The user can specify a mapping of values, ranges, or pre-defined categories, along with the level to which these values should be interpreted.
2. Performance costs is almost entirely paid for at startup by building a full mapping which can then be used for instant interpretation of any value.

Describe the solution you'd like

The primary challenge with OTTL is that its functional nature may not lend itself well to specifying mappings. I'm not sure if there is a way to do this today, but I'd like users to be able to specify a function that contains an arbitrary number of mapping options. e.g. ParseSeverity(attributes["sev"], AsError("err", "error", "NOOO"), AsInfo("info", "hey"), AsInfoRange(1, 100), ...)

Describe alternatives you've considered

No response

Additional context

No response

[github-actions]

Pinging code owners:

• pkg/ottl: @TylerHelmuth @kentquirk @bogdandrutu @evan-bradley

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[TylerHelmuth]

@djaglowski we support map literals now, will that help? The grammar supports:

ParseSeverity(attributes["sev"], {"err": ["error", "NOOO"], "info": ["hey"]})

As a reference for discussion, the existing solution would be multiple statements with conditions:

set(severity_number, SEVERITY_NUMBER_ERROR) where attributes["sev"] == "error" or attributes["sev"] == "NOOO"
set(severity_number, SEVERITY_NUMBER_INFO) where attributes["sev"] == "hey" or (attributes["status code"] >= 1 and attributes["status code"] < 100) 

Any additional function will need to be simpler than those statements.

[TylerHelmuth]

It is possible that the solution doesn't need to be an additional function and instead could be a additional section in the transformprocessor config.

[djaglowski]

we support map literals now, will that help?

I don't think this is sufficient for ranges, which are a common use case with severity interpretation.

Any additional function will need to be simpler than those statements.

I don't think that's difficult but performance should also be a consideration here.

---

I'll give another example of statements which could be much clearer and more performant with a better solution.

In this case, HTTP status codes are interpreted into severity number and text:

set(severity_number, 5) where (IsMatch(body["status"], "^1[0-9]{2}$") and true)
set(severity_text, "debug") where (IsMatch(body["status"], "^1[0-9]{2}$") and true)
set(severity_number, 9) where (IsMatch(body["status"], "^2[0-9]{2}$") and true)
set(severity_text, "info") where (IsMatch(body["status"], "^2[0-9]{2}$") and true)
set(severity_number, 9) where (IsMatch(body["status"], "^3[0-9]{2}$") and true)
set(severity_text, "info") where (IsMatch(body["status"], "^3[0-9]{2}$") and true)
set(severity_number, 13) where (IsMatch(body["status"], "^4[0-9]{2}$") and true)
set(severity_text, "warn") where (IsMatch(body["status"], "^4[0-9]{2}$") and true)
set(severity_number, 17) where (IsMatch(body["status"], "^5[0-9]{2}$") and true)
set(severity_text, "error") where (IsMatch(body["status"], "^5[0-9]{2}$") and true)

This is both difficult to understand and not very performant since each statement must execute against each log record, and because the statements themselves are non-trivial to evaluate.

In contrast, the stanza is far simpler to understand:

severity:
  parse_from: body["status"]
  mapping:
    debug:
      - min: 100
        max: 199
    info:
      - min: 200
        max: 299
      - min: 300
        max: 399
    warn:
      - min: 400
        max: 499
    error:
      - min: 500
        max: 599

# (Actually it can be even simpler but this is a special case where aliases represent predefined ranges)
# mapping:
#   debug: 1xx
#   info:
#     - 2xx
#     - 3xx
#   warn: 4xx
#   error: 5xx

Additionally, there is a substantial performance optimization which occurs with the stanza configuration. Specifically, we're able to put all values into a map at startup, so that every log records requires exactly one map lookup.

I don't have strong opinions about exactly which form this should take in OTTL but I think it should be supported in some way that avoids such dense and wasteful statements.