Get controller labels from controller, not params #293
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prometheus_exporter currently reads the controller and action label from action_dispatch.request.parameters. This can lead to conflicts, where there's a form parameter called "action", or "controller" which takes precedence over "which controller action is this?". This can be validated with a curl request to a rails application instrumented with prometheus_exporter: curl -v http://127.0.0.1:3000/ --data 'controller=test' Results in: # HELP http_requests_total Total HTTP requests from web app. # TYPE http_requests_total counter http_requests_total{action="other",controller="test",status="404"} 1 This commit pulls the controller instance from `action_controller.instance`, and then calls the controller_name / action_name methods, which should be accurate even when conflicting form parameters are provided.
richardTowers
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Oct 3, 2023
I've got an open PR to do this for the default default in prometheus_exporter itself: github[.]com/discourse/prometheus_exporter/pull/293 But it's unclear whether the maintainers will accept that, and if so how long that will take. In the meantime, we've got quite a bit of noise in our metrics because it's currently possible for an HTTP request to overwrite the action / controller labels by passing them in as request parameters like this: curl -v http://127.0.0.1:3000/ --data 'controller=test' This commit extends the default middleware so we have more sensible defaults for both Rails and Sinatra apps. I couldn't work out any good labels for sinatra apps that wouldn't be potentially high cardinality, so those are just blank.
richardTowers
added a commit
to alphagov/govuk_app_config
that referenced
this pull request
Oct 3, 2023
I've got an open PR to do this for the default default in prometheus_exporter itself: github.com/discourse/prometheus_exporter/pull/293 But it's unclear whether the maintainers will accept that, and if so how long that will take. In the meantime, we've got quite a bit of noise in our metrics because it's currently possible for an HTTP request to overwrite the action / controller labels by passing them in as request parameters like this: curl -v http://127.0.0.1:3000/ --data 'controller=test' This commit extends the default middleware so we have more sensible defaults for both Rails and Sinatra apps. I couldn't work out any good labels for sinatra apps that wouldn't be potentially high cardinality, so those are just blank.
richardTowers
added a commit
to alphagov/govuk_app_config
that referenced
this pull request
Oct 3, 2023
I've got an open PR to do this for the default default in prometheus_exporter itself: github.com/discourse/prometheus_exporter/pull/293 But it's unclear whether the maintainers will accept that, and if so how long that will take. In the meantime, we've got quite a bit of noise in our metrics because it's currently possible for an HTTP request to overwrite the action / controller labels by passing them in as request parameters like this: curl -v http://127.0.0.1:3000/ --data 'controller=test' This commit extends the default middleware so we have more sensible defaults for both Rails and Sinatra apps. I couldn't work out any good labels for sinatra apps that wouldn't be potentially high cardinality, so those are just blank.
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prometheus_exporter currently reads the controller and action label from action_dispatch.request.parameters. This can lead to conflicts, where there's a form parameter called "action", or "controller" which takes precedence over "which controller action is this?".
This can be validated with a curl request to a rails application instrumented with prometheus_exporter:
Results in:
This commit pulls the controller instance from
action_controller.instance, and then calls the controller_name / action_name methods, which should be accurate even when conflicting form parameters are provided.I haven't added any new tests for this, but I have tested it locally (by pointing a local rails app at a local copy of the gem, and doing the curl request above). Please let me know if you'd like a test (I might need a hint as to where to put it though).