[noderesourcetopology] update NRT when attributes change #631
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[APPROVALNOTIFIER] This PR is APPROVED This pull-request has been approved by: ffromani The full list of commands accepted by this bot can be found here. The pull request process is described here
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A upcoming change in the overreserve cache wants to consume nodeconfig utilities, so in order to enable both packages to consume this code, we move it in its own package. Trivial code movement and only necessary interface changes (renames/public <-> private symbols). Signed-off-by: Francesco Romani <[email protected]>
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the integration test is pretty much done but thare are known issues I'm investigating. |
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/cc @Tal-or |
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One of the key assumptions we took when designing the NodeResourceTopology (NRT) plugin is that the kubelet configuration of the worker node changes *very* rarely, if at all, during the cluster lifetime. As rule of thumb, it was expected to change with a frequency of like once every quarter (3 months) or so, and likely less often. So the event of changing during a scheduling cycle was deemed extremely low. However, we fail to notice kubelet configuration changes (the bits we care reported by NRT data) and we update them incidentally when resyncing the cache. These updates are expected to be rare, but still failing to noticing them is a much worse issue: with out of date configuration information, the scheduler plugin will take wrong decisions until restarted. Up until now, the mitigation was to restart the scheduler once kubelet config changes; this works, but it is unpractical and requires more orchestration. We add the option to resync the NRT data if the attribute change (and nothing else did) to overcome this limitation. In the current framework, because of how controller-runtime/client works, this will require a new connection to the apiserver to watch the changes and react to them, adding the node to the set of the one being resynced in the next resync iteration. Even considering HA scheduler scenarios, this will cause a very limited amount of new connections, and should not cause any scalability concern. Nevertheless, we make the feature opt-in. Signed-off-by: Francesco Romani <[email protected]>
Switch the default and prefer correctness over backward compatibility, because the previous behavior was buggy (see: kubernetes-sigs#621) Signed-off-by: Francesco Romani <[email protected]>
That's a good point. We add a extra watch, but previously the behavior was arguably buggy. Let me switch the defaults. |
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/hold Hold letting other reviews time to chime in |
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@PiotrProkop howdy! Do you have any comments by any chance? |
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@ffromani sorry I was on vacations. Looks good to me! |
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What type of PR is this?
/kind bug
What this PR does / why we need it:
One of the key assumptions we took when designing the NodeResourceTopology (NRT) plugin is that the kubelet config of the worker node changes VERY rarely, if at all, during the cluster lifetime. As rule of thumb, it was expected to change with a frequency of like once every quarter (3 months) or so, and likely less often. So the event of changing during a scheduling cycle was deemed extremely low.
However, we fail to notice kubelet configuration changes (the bits we care reported by NRT data) and we update them incidentally when resyncing the cache.
These updates are expected to be rare, but still failing to noticing them is a different issue because it can lead to unnecessarily bad scheduling decision.
Simply put, failing to noticing these updates is a gap, which we address with this PR
Which issue(s) this PR fixes:
Fixes #621
Special notes for your reviewer:
still WIP, more test ongoing and upcoming
Does this PR introduce a user-facing change?