Add features flag API proposal #63

roidelapluie · 2025-10-16T12:20:22Z

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bwplotka

Nice! I like this, will review in details later on

roidelapluie · 2025-10-21T14:20:32Z

Here's what I get so far with PromQL:

{
  "status": "success",
  "data": {
    "promql": {
      "at_modifier": true,
      "delayed_name_removal": false,
      "experimental_duration_expr": false,
      "extended_range_selectors": false,
      "negative_offset": true,
      "per_query_lookback_delta": true,
      "per_step_stats": false,
      "subqueries": true,
      "type_and_unit_labels": false
    },
    "promql_functions": {
      "abs": true,
      "absent": true,
      "absent_over_time": true,
      "acos": true,
      "acosh": true,
      "asin": true,
      "asinh": true,
      "atan": true,
      "atanh": true,
      "avg_over_time": true,
      "ceil": true,
      "changes": true,
      "clamp": true,
      "clamp_max": true,
      "clamp_min": true,
      "cos": true,
      "cosh": true,
      "count_over_time": true,
      "day_of_month": true,
      "day_of_week": true,
      "day_of_year": true,
      "days_in_month": true,
      "deg": true,
      "delta": true,
      "deriv": true,
      "double_exponential_smoothing": false,
      "exp": true,
      "first_over_time": false,
      "floor": true,
      "histogram_avg": true,
      "histogram_count": true,
      "histogram_fraction": true,
      "histogram_quantile": true,
      "histogram_stddev": true,
      "histogram_stdvar": true,
      "histogram_sum": true,
      "hour": true,
      "idelta": true,
      "increase": true,
      "info": false,
      "irate": true,
      "label_join": true,
      "label_replace": true,
      "last_over_time": true,
      "ln": true,
      "log10": true,
      "log2": true,
      "mad_over_time": false,
      "max_over_time": true,
      "min_over_time": true,
      "minute": true,
      "month": true,
      "pi": true,
      "predict_linear": true,
      "present_over_time": true,
      "quantile_over_time": true,
      "rad": true,
      "rate": true,
      "resets": true,
      "round": true,
      "scalar": true,
      "sgn": true,
      "sin": true,
      "sinh": true,
      "sort": true,
      "sort_by_label": false,
      "sort_by_label_desc": false,
      "sort_desc": true,
      "sqrt": true,
      "stddev_over_time": true,
      "stdvar_over_time": true,
      "sum_over_time": true,
      "tan": true,
      "tanh": true,
      "time": true,
      "timestamp": true,
      "ts_of_first_over_time": false,
      "ts_of_last_over_time": false,
      "ts_of_max_over_time": false,
      "ts_of_min_over_time": false,
      "vector": true,
      "year": true
    },
    "promql_operators": {
      "!=": true,
      "!~": true,
      "%": true,
      "*": true,
      "+": true,
      "-": true,
      "/": true,
      "<": true,
      "<=": true,
      "==": true,
      "=~": true,
      ">": true,
      ">=": true,
      "@": true,
      "^": true,
      "and": true,
      "atan2": true,
      "avg": true,
      "bottomk": true,
      "count": true,
      "count_values": true,
      "group": true,
      "limit_ratio": false,
      "limitk": false,
      "max": true,
      "min": true,
      "or": true,
      "quantile": true,
      "stddev": true,
      "stdvar": true,
      "sum": true,
      "topk": true,
      "unless": true
    }
  }
}

bboreham · 2025-10-27T18:00:51Z

Here's what I get so far with PromQL:

I like the proposal, but I feel that list is too granular. I don't think it's useful to list features and functions which have existed in PromQL for years. So limitk is useful but topk is not.

roidelapluie · 2025-10-28T09:40:51Z

Here's what I get so far with PromQL:

I like the proposal, but I feel that list is too granular. I don't think it's useful to list features and functions which have existed in PromQL for years. So limitk is useful but topk is not.

To avoid drifting from the actual code, the list is auto-generated. Note that I do not expect users of the API to check if "rate" is supported before using it.

dimitarvdimitrov · 2025-10-28T15:26:40Z

proposals/0063-feature-flag.md

+3. New Prometheus-compatible backends require explicit code changes in Grafana, slowing adoption.
+4. Type and version checks are coarse; they do not reflect actual enabled features, which may depend on flags or configuration.
+
+There is no real alternative to this for now.


what we use in mimir is the buildinfo endpoint by adding a features field to the response.

Grafana already uses that for some alertmanager features.

thanks, I added that to the design doc.

dimitarvdimitrov · 2025-10-28T15:29:00Z

proposals/0063-feature-flag.md

+- The response follows standard Prometheus API conventions with `status` and `data` fields
+- The endpoint returns HTTP 200 OK, like other Prometheus APIs
+
+Some items might exist in multiple categories.


won't this make it harder for clients to integrate with the endpoint? They'd need to search for the same feature in multiple categories and handle cases where the feature appears in one category but not the other

What I meant is that I did not want to restrict some items to some categories. But I can remove this sentence from the design doc, not to encourage duplication of elements.

roidelapluie · 2025-10-30T15:53:20Z

Here's the content of the features API currently:

https://github.com/prometheus/prometheus/blob/680eb81c890b99c2f2a31f370a4eea8f3e787c1d/cmd/prometheus/testdata/features.json

proposals/0063-feature-flag.md

Signed-off-by: Julien Pivotto <[email protected]>

bwplotka

This is great, thanks. LGTM from my side.

For consistency it would be fun to enable some ff to be dynamically settable (via runtime config/HTTP), but that's a separate discussion. I'd love feature flags to be a separate package in Go code so we can consistently used it everywhere too, likely an after effect of the implementation of this PROM-63.

I found categorization very odd at the first glance, similar to @bboreham. Like why we have a mix in this API feature flags, build tags (stringlabels), PromQL functions, PromQL operators and even mode (agent). Then we already have endpoints that give some of this info like build info, flags.

What got me sold is the simplified way of accessing the info of what's the current Prometheus process is "capable of" which is a mix of those flags, Prometheus exact version, the tag it was used with and even build options like what SD providers were build with. Then it's also great for 4.x and 5.x where we might kill some features (improving feature lifecycle maintenance). So this is super useful 👍🏽

proposals/0063-feature-flag.md

roidelapluie · 2025-11-04T09:29:49Z

This is great, thanks. LGTM from my side.

I found categorization very odd at the first glance, similar to @bboreham. Like why we have a mix in this API feature flags, build tags (stringlabels), PromQL functions, PromQL operators and even mode (agent). Then we already have endpoints that give some of this info like build info, flags.

I can review this and filter down to only have the layer of "useful" things that can be used externally (e.g. remove agent and TSDB features). Keeping PromQL and API-related things.

What got me sold is the simplified way of accessing the info of what's the current Prometheus process is "capable of" which is a mix of those flags, Prometheus exact version, the tag it was used with and even build options like what SD providers were build with. Then it's also great for 4.x and 5.x where we might kill some features (improving feature lifecycle maintenance). So this is super useful 👍🏽

The goal is NOT to expose Prometheus exact version, so that it does not matter if you query Prometheus, Thanos, Cortex, ...

bwplotka · 2025-11-04T13:56:23Z

I can review this and filter down to only have the layer of "useful" things that can be used externally (e.g. remove agent and TSDB features). Keeping PromQL and API-related things.

Sorry for confusion, I was explaining my train of thoughts 🙈 While initially odd, I think I like the low level details here.

The goal is NOT to expose Prometheus exact version, so that it does not matter if you query Prometheus, Thanos, Cortex, ...

Yup yes! That's why I approved (:

Co-authored-by: Bartlomiej Plotka <[email protected]> Signed-off-by: Julien <[email protected]>

Signed-off-by: Julien Pivotto <[email protected]>

roidelapluie · 2025-11-17T09:03:03Z

If there is no further comments, I am planning to merge this in 48 hours.

roidelapluie force-pushed the roidelapluie/ffapi branch 2 times, most recently from 9997ef7 to 84cf2d0 Compare October 16, 2025 12:27

roidelapluie mentioned this pull request Oct 16, 2025

Feature request: add a "features supported" API prometheus/prometheus#10022

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roidelapluie force-pushed the roidelapluie/ffapi branch from 964e418 to 2a249d6 Compare November 3, 2025 10:47

Add features flag API proposal

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Signed-off-by: Julien Pivotto <[email protected]>

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roidelapluie and others added 2 commits November 17, 2025 09:55

Update proposals/0063-feature-flag.md

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Co-authored-by: Bartlomiej Plotka <[email protected]> Signed-off-by: Julien <[email protected]>

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Signed-off-by: Julien Pivotto <[email protected]>

Add features flag API proposal #63

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roidelapluie commented Nov 17, 2025 •

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