enhancement(tag_cardinality_limit transform): Add metric and tag name to tag_value_limit_exceeded_total metric

[kaarolch]

Summary

When using the tag_cardinality_limit transform, it's difficult to identify which specific metrics and tag keys are hitting the configured value limit. The tag_value_limit_exceeded_total metric only provides a count of exceeded events without context about which metric or tag was blocked, making it challenging to debug and monitor cardinality issues.
More in #20084

This PR adds metric_name and tag_key labels to the tag_value_limit_exceeded_total metric and allowing:

• Identify which specific metrics are hitting the limit
• Identify which tag keys are causing the limit to be exceeded
• Create more targeted alerts and dashboards

Vector configuration

sources:
  vector_metrics:
    type: "internal_metrics" # required
    scrape_interval_secs: 10 
  statsd:
    type: statsd
    address: "0.0.0.0:8128"
    mode: "udp"

transforms:
  metrics_cardinality_limit:
    type: tag_cardinality_limit
    inputs:
      - statsd
    limit_exceeded_action: drop_tag
    internal_metrics:
      include_extended_tags: true
    mode: exact
    value_limit: 10
sinks:
  drop_bh:
    type: blackhole
    inputs:
      - metrics_cardinality_limit
    print_interval_secs: 0
    buffer:
      type: memory
      when_full: drop_newest
      max_events: 100
  console_debug:
    type: console
    inputs:
      -  vector_metrics
    encoding:
      codec: json
    buffer:
       max_events: 10000
       type: memory
       when_full: drop_newest

How did you test this PR?

Build locally based on docs/DEVELOPING.md and start with config mentioned in the previous section :

target/debug/vector --config ../vector.yaml

Result:

{"name":"tag_value_limit_exceeded_total","namespace":"vector","tags":{"component_id":"metrics_cardinality_limit","component_kind":"transform","component_type":"tag_cardinality_limit","host":"xxxx","metric_name":"high_cardinality_metric_gauge_1","tag_key":"pod_name"},"timestamp":"2025-11-13T20:10:30.055509Z","kind":"absolute","counter":{"value":7470.0}}

When internal_metrics.include_extended_tags: false:

{"name":"tag_value_limit_exceeded_total","namespace":"vector","tags":{"component_id":"metrics_cardinality_limit","component_kind":"transform","component_type":"tag_cardinality_limit","host":"xxxx"},"timestamp":"2025-11-19T09:19:20.321422Z","kind":"absolute","counter":{"value":2430.0}}

Change Type

• Bug fix
• New feature
• Non-functional (chore, refactoring, docs)
• Performance

Is this a breaking change?

• Yes
• No

Does this PR include user facing changes?

• Yes. Please add a changelog fragment based on our guidelines.
• No. A maintainer will apply the no-changelog label to this PR.

References

Notes

• Please read our Vector contributor resources.
• Do not hesitate to use @vectordotdev/vector to reach out to us regarding this PR.
• Some CI checks run only after we manually approve them.
  • We recommend adding a pre-push hook, please see this template.
  • Alternatively, we recommend running the following locally before pushing to the remote branch:
    • make fmt
    • make check-clippy (if there are failures it's possible some of them can be fixed with make clippy-fix)
    • make test
• After a review is requested, please avoid force pushes to help us review incrementally.
  • Feel free to push as many commits as you want. They will be squashed into one before merging.
  • For example, you can run git merge origin master and git push.
• If this PR introduces changes Vector dependencies (modifies Cargo.lock), please
  run make build-licenses to regenerate the license inventory and commit the changes (if any). More details here.

[domalessi]

A few suggestions but looks good

[kaarolch]

btw. Should we add more label? This PR introduces two new tags to an internal metric for the tag_cardinality_limit transform.

[github-actions]

All contributors have signed the CLA ✍️ ✅
_{Posted by the CLA Assistant Lite bot.}

[kaarolch]

I have read the CLA Document and I hereby sign the CLA

[kaarolch]

recheck

[kaarolch]

@pront let me know if something is still missing or maybe need to be better handle.

[kaarolch]

@vectordotdev/vector is there anything that block this PR? Let me know if there is anything to change.

[kaarolch]

@pront any other concerns about this PR?

[kaarolch]

Any update?

[kaarolch]

Hi @vectordotdev/vector,
is there any chance to review this PR?

[pront]

Hi @kaarolch, thanks for this PR. I was OOO for a while. This PR mostly looks good to me. Left new comments.

[kaarolch]

@pront I've followed your sugestions and updated a config param.

[kaarolch]

I've updated doc and commited missed test change.

[kaarolch]

Local check pass:

• make fmt ✅
• make check-clippy ✅
• make check-docs ✅
• make test ✅

[kaarolch]

@pront sorry to ping you one again, can you rerun the waiting action?

[kaarolch]

It looks like run local make check-docs pass but run remote GHA doesn't pass:

make check-docs
cargo vdev check docs
Skipping cue files format validation - reserved for CI
Validating cue files correctness...
Success! The contents of the sources in the "./website/cue" directory are valid

It's strange because I used command make generate-component-docs and cd rust-doc && make docs for doc generation.

Anyway when I run test locally with:

CI=true make check-docs 2>&1
error: failed to run custom build command for `libssh2-sys v0.3.1`

Caused by:
  process didn't exit successfully: `/var/folders/nd/2yzp3fys4c14w_fr6gdjb5_w0000gq/T/cursor-sandbox-cache/71e5d7b90b9169d20c7dbbfcba3ec828/cargo-target/debug/build/libssh2-sys-9853a274f0a12f64/build-script-build` (exit status: 101)
  --- stdout
  cargo:rerun-if-env-changed=LIBSSH2_SYS_USE_PKG_CONFIG
  cargo:include=/var/folders/nd/2yzp3fys4c14w_fr6gdjb5_w0000gq/T/cursor-sandbox-cache/71e5d7b90b9169d20c7dbbfcba3ec828/cargo-target/debug/build/libssh2-sys-e3a21bbcc12dc641/out/include
  cargo:root=/var/folders/nd/2yzp3fys4c14w_fr6gdjb5_w0000gq/T/cursor-sandbox-cache/71e5d7b90b9169d20c7dbbfcba3ec828/cargo-target/debug/build/libssh2-sys-e3a21bbcc12dc641/out
....

When I ran command locally ./scripts/cue.sh fmt, the CI=true pass:

CI=true make check-docs 2>&1
cargo vdev check docs
Validating cue files formatting...
Validating cue files correctness...
Success! The contents of the sources in the "./website/cue" directory are valid

I've pushed commit and now pipeline should pass
Local test looks correct.