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https://issues.apache.org/jira/browse/FLINK-21309?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17280706#comment-17280706
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Chesnay Schepler commented on FLINK-21309:
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Doing a POST is a dangerous approach. Various labels increase in cardinality
over time, like process IDs, (Flink) job IDs (for session clusters) or attempt
numbers.
With a POST we'd end up adding more and more metrics to the PushGateway,
eventually overloading it, because nothing is ever deleted. As such, I would
recommend you to stop instructing other people to use POST, as it may impact
the stability of their infrastructure.
PUT allows us to remove old metrics from the PushGateway that no longer exists.
Unfortunately the PushGateway does not provide us with any better means of
deleting old metrics, like a time-to-live parameter or being able to delete
metrics by label.
> Metrics of JobManager and TaskManager overwrite each other in pushgateway
> -------------------------------------------------------------------------
>
> Key: FLINK-21309
> URL: https://issues.apache.org/jira/browse/FLINK-21309
> Project: Flink
> Issue Type: Bug
> Components: Runtime / Metrics
> Affects Versions: 1.9.0, 1.10.0, 1.11.0
> Environment: 1. Components :
> Flink 1.9.0/1.10.0/1.11.0 + Prometheus + Pushgateway + Yarn
> 2. Metrics Configuration in flink-conf.yaml :
> {code:java}
> metrics.reporter.promgateway.class:
> org.apache.flink.metrics.prometheus.PrometheusPushGatewayReporter
> metrics.reporter.promgateway.jobName: myjob
> metrics.reporter.promgateway.randomJobNameSuffix: false{code}
>
> Reporter: jiguodai
> Priority: Major
> Attachments: image-2021-02-05-21-07-42-292.png
>
> Original Estimate: 12h
> Remaining Estimate: 12h
>
> When a flink job run on yarn, metrics of jobmanager and taskmanagers will
> overwrite each other. The phenomenon is that on one second you can find only
> jobmanager metrics on pushgateway web ui, while on the next second you can
> find only taskmanager metrics on pushgateway web ui, these two kinds of
> metrics appear alternately. One metric of taskmanager on grafana will be like
> below intermittently (this taskmanager metric disappear on grafana when
> jobmanager metrics overwrite taskmanager metrics):
> !image-2021-02-05-21-07-42-292.png!
> The real reason is that Flink PrometheusPushGatewayReporter use PUT style
> instead of POST style to push metrics to pushgateway, what's more,
> taskmanagers and jobmanager use the same jobName (the only grouping key)
> which we configured in flink-conf.yaml.
> Althought REST URLs are same as below,
> {code:java}
> /metrics/job/<JOB_NAME>{/<LABEL_NAME>/<LABEL_VALUE>}
> {code}
> PUT and POST caused different results, as we can see below :
> * PUT is used to push a group of metrics. All metrics with the grouping key
> specified in the URL are replaced by the metrics pushed with PUT.
> * POST works exactly like the PUT method but only metrics with the same name
> as the newly pushed metrics are replaced.
> For these reasons, it's better to use POST style to push metrics to
> pushgateway to prevent jobmanager metrics and taskmanager metrics from
> overwriting each other, so that we can get continuous graph on grafana. Maybe
> you will say that we can set
> {code:java}
> metrics.reporter.promgateway.randomJobNameSuffix: true{code}
> in flink-conf.yaml, in this way, jobName from different nodes will has a
> random suffix and metrics will not overwrite each other any more. While we
> should be aware that most of users tend to use jobName as filter condition in
> PromQL, and using regular expressions to find exact jobName will degrade the
> speed of data retrieval in prometheus.
> Everytime some body ask why metrics on grafana is discontinuous on Flink
> mailing list, i will tell him that you should change the style of pushing
> metrics to pushgateway from PUT to POST and then repackage the
> flink-metrics-prometheus module. So, why don't we solve the problem
> permanently now ? I hope to have the chance to solve the problem, sincerely.
> related links :
> [https://github.com/prometheus/pushgateway#put-method]
> [https://github.com/prometheus/pushgateway/issues/308]
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