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tips-for-scaling-rancher: clarify language on etcd recommendations

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Signed-off-by: Silvio Moioli <silvio@moioli.net>
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Silvio Moioli
2023-10-02 11:12:41 +02:00
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docs/reference-guides/best-practices/rancher-server/tips-for-scaling-rancher.md
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@@ -62,6 +62,8 @@ A large component of performance is the local cluster and how it was configured.
Similar to Rancher versions, it is advisable to keep your kubernetes cluster up to date. This will ensure that your cluster contains any available performance enhancements or bug fixes.
### Optimizing etcd
The two main bottlenecks to [etcd performance](https://etcd.io/docs/v3.4/op-guide/performance/) are disk speed and network speed. Optimization to either should improve performance. For information regarding etcd performance see [Slow etcd performance (performance testing and optimization)](https://www.suse.com/support/kb/doc/?id=000020100) and [Tuning etcd for Large Installations](https://docs.ranchermanager.rancher.io/how-to-guides/advanced-user-guides/tune-etcd-for-large-installs). Information on disks can also be found [in our docs](https://docs.Ranchermanager.Rancher.io/v2.5/pages-for-subheaders/installation-requirements#disks).
The two main bottlenecks to [etcd performance](https://etcd.io/docs/v3.4/op-guide/performance/) are disk speed and network speed. It is thus recommended that etcd runs on dedicated nodes with SSDs with high IOPS and a fast network setup. For more information regarding etcd performance see [Slow etcd performance (performance testing and optimization)](https://www.suse.com/support/kb/doc/?id=000020100) and [Tuning etcd for Large Installations](../../../how-to-guides/advanced-user-guides/tune-etcd-for-large-installs). Information on disks can also be found in the [Installation Requirements](../../../pages-for-subheaders/installation-requirements#disks) page.
Theoretically, the more nodes in an etcd cluster the slower it will be due to replication requirements [source](https://etcd.io/docs/v3.3/faq). This may be counter-intuitive to common scaling approaches. It can also be inferred that etcd performance will be inversely affected by distance between nodes as that will slow down network communication.
As adding more nodes in an etcd cluster will make operations slower, for best performance it is recommended to run etcd on exactly 3 nodes. This may be counter-intuitive to common scaling approaches, and it is due to etcd's [replication mechanisms](https://etcd.io/docs/v3.5/faq/#what-is-maximum-cluster-size).
etcd performance will also be negatively affected by network latency between nodes as that will slow down network communication, so it is recommended that etcd nodes are all colocated together with Rancher nodes.