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https://issues.apache.org/jira/browse/HDDS-16019?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18100036#comment-18100036
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arun kumar commented on HDDS-16019:
-----------------------------------
One design question before implementing.
Replicating BaseHttpServer's /prom wiring from the httpfs package isn't clean:
both BaseHttpServer.PROMETHEUS_SINK and HttpServer2.getWebAppContext() are
package-private (org.apache.hadoop.hdds.server.http). BaseHttpServer sets the
sink via getWebAppContext().getServletContext().setAttribute(PROMETHEUS_SINK,
sink), neither of which is reachable from org.apache.ozone.fs.http.server.
There is a public HttpServer2.setAttribute(), but it sets on the webapp context
rather than the servlet context PrometheusServlet reads from, so it isn't a
drop-in.
So rather than widening visibility on several framework internals, I'd lean
toward extracting the sink + PrometheusServlet wiring into a small shared
helper in org.apache.hadoop.hdds.server.http, called by both BaseHttpServer and
HttpFSServerWebServer. Slightly more than a one-liner in BaseHttpServer, but no
widened API surface and it removes the duplication. The secure-mode guarantees
(bearer-token internal servlet when a token is set, otherwise behind the auth
filter) carry over unchanged.
Does that approach sound good, or would you prefer just making the needed
members public? cc: [~erose]
cc:
> Publish httpfs gateway metrics to Prometheus via /prom endpoint
> ---------------------------------------------------------------
>
> Key: HDDS-16019
> URL: https://issues.apache.org/jira/browse/HDDS-16019
> Project: Apache Ozone
> Issue Type: Improvement
> Reporter: arun kumar
> Assignee: arun kumar
> Priority: Major
>
> HttpFSServerWebServer builds an HttpServer2 directly rather than
> extending BaseHttpServer, so unlike OM, SCM, Datanode, S3 Gateway,
> and Recon it does not expose a /prom endpoint. As a result the
> metrics already registered on the httpfs JVM (e.g. HttpFSServerMetrics)
> cannot be scraped by Prometheus, and httpfs is absent from
> compose/ozone/prometheus.yml and from component-grouped Grafana
> dashboards.
>
> {{Proposed change:}}
> * Register a PrometheusMetricsSink and add the PrometheusServlet at
> /prom in HttpFSServerWebServer, following the pattern in
> BaseHttpServer (guarded by hdds.prometheus.endpoint.enabled).
> * Register the sink with DefaultMetricsSystem on start(), unregister
> on stop().
> * Ensure /prom respects the same authentication guarantees as the
> other services in secure mode (not exposed unauthenticated).
>
> Note: BaseHttpServer.PROMETHEUS_SINK is currently package-private;
> exposing /prom from the httpfs package needs either that constant
> made public or the wiring extracted into a shared helper. Open to
> either – will confirm on review.
>
> This is a prerequisite for HDDS-15858 (build info metrics + ZDU
> dashboard), which will add the httpfs scrape target and build info
> on top once /prom exists.
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