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Add a section about nodelocaldns memory limits.

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prameshj 2022-01-30 21:10:40 -08:00 committed by GitHub
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content/en/docs/tasks/administer-cluster/nodelocaldns.md
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@ -100,4 +100,16 @@ shown in [the example](/docs/tasks/administer-cluster/dns-custom-nameservers/#ex
The `node-local-dns` ConfigMap can also be modified directly with the stubDomain configuration
in the Corefile format. Some cloud providers might not allow modifying `node-local-dns` ConfigMap directly.
In those cases, the `kube-dns` ConfigMap can be updated.
## Setting Memory limits
node-local-dns pods use memory for storing cache entries and processing queries. Since they do not watch Kubernetes objects, the cluster size or the number of Services/Endpoints do not affect memory usage. Memory usage is influenced by the DNS query pattern.
From [CoreDNS docs](https://github.com/coredns/deployment/blob/master/kubernetes/Scaling_CoreDNS.md),
`The default cache size is 10000 entries, which uses about 30 MB when completely filled.`
This would be the memory usage for each server block (if the cache gets completely filled).
Memory usage can be reduced by specifying smaller cache sizes.
The number of concurrent queries can lead to additional memory usage (more goroutines). An upper limit can be set via the "max_concurrent" option in the forward plugin.
If a node-local-dns pod gets OOMKilled, it will not cleanup the custom iptables rules added at startup time. The node-local-dns pod should get restarted(since it is part of a daemonset), but this will lead to a brief DNS downtime everytime the pod crashes. A suitable memory limit can be determined by running node-local-dns pods without a limit and measuring the peak usage.