GovukPrometheus - custom labels from rack env #424
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theseanything
approved these changes
Jan 15, 2025
Apps can use request.env['govuk.prometheus_labels'] to specify custom
labels for prometheus.
For example, and app might do:
prometheus_labels = request.env.fetch('govuk.prometheus_labels', {})
request.env['govuk.prometheus_labels'] = prometheus_labels.merge(
document_type: @content_item.document_type,
schema_name: @content_item.schema_name,
)
To set the document type / schema name as custom labels (which is useful
for the apps where this isn't obvious based on controller / action, like
government-frontend)
Testing locally, this results in metrics like:
http_request_duration_seconds_count{action="show",controller="content_items",document_type="answer",schema_name="answer"} 1
Care does need to be taken with the cardinality of prometheus labels
(i.e. there shouldn't be too many different combinations of labels), but
things like document_type are useful and shouldn't increase cardinality
too much.
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richardTowers
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Jan 15, 2025
This will allow us to investigate the performance of different content types, for example how long does it take to load a manual vs. an answer or a case_study. If there are some content types which take a much longer time to load, maybe there are performance issues we should address. This follows on from alphagov/govuk_app_config#424 which adds the functionality to support setting prometheus labels in this way.
richardTowers
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to alphagov/government-frontend
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Jan 15, 2025
This will allow us to investigate the performance of different content types, for example how long does it take to load a manual vs. an answer or a case_study. If there are some content types which take a much longer time to load, maybe there are performance issues we should address. This follows on from alphagov/govuk_app_config#424 which adds the functionality to support setting prometheus labels in this way.
richardTowers
added a commit
to alphagov/government-frontend
that referenced
this pull request
Jan 15, 2025
This results in metrics like:
http_requests_total{action="show",controller="content_items",document_type="answer",schema_name="answer",status="200"} 1
This will allow us to investigate the performance of different content
types, for example how long does it take to load a manual vs. an answer
or a case_study. Currently we can't distinguish these in the metrics for
government-frontend, because it uses the same controller action for all
content types.
If there are some content types which take a much longer time to load,
maybe there are performance issues we should address.
This follows on from alphagov/govuk_app_config#424
which adds the functionality to support setting prometheus labels in this way.
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Apps can use request.env['govuk.prometheus_labels'] to specify custom labels for prometheus.
For example, and app might do:
To set the document type / schema name as custom labels (which is useful for the apps where this isn't obvious based on controller / action, like government-frontend)
Testing locally, this results in metrics like:
Care does need to be taken with the cardinality of prometheus labels (i.e. there shouldn't be too many different combinations of labels), but things like document_type are useful and shouldn't increase cardinality too much.