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Note regarding mega nodes #3823

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Note regarding mega nodes
Tejeev Jan 25, 2022
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Update content/rke/latest/en/os/_index.md
Tejeev Mar 23, 2022
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Expand Up @@ -297,7 +297,17 @@ Regarding CPU and memory, it is recommended that the different planes of Kuberne

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Is there a reason we put this in the rke docs ? Wouldn't this apply to any large cluster, including rke2.
We need to make a scaling section, but for now most of that data lives over here: https://rancher.com/docs/rancher/v2.5/en/installation/requirements/

### Large Kubernetes Clusters

For hardware recommendations for large Kubernetes clusters, refer to the official Kubernetes documentation on [building large clusters](https://kubernetes.io/docs/setup/best-practices/cluster-large/).
Kubernetes is engineered around the concept of horizontal scaling for redundancy, so scaling vertically with large servers can be problematic if the proper minimum/maximum requirements aren’t followed. The following are tips and recommendations for large Kubernetes clusters:

- If you must use servers larger than 24 CPU, use virtualization tooling, such as what [Harvester](https://docs.harvesterhci.io/v1.0/rancher/virtualization-management/) provides, to subdivide the servers.
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If you must use servers larger than 24 CPU

Where did that 24 CPU number come from ?


- Kubernetes, kernel, and network limitations prevent having too many pods per server. You should maintain a minimum of roughly 24 cores per server and a maximum of the recommended 110 pods per server.
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- Kubernetes, kernel, and network limitations prevent having too many pods per server. You should maintain a minimum of roughly 24 cores per server and a maximum of the recommended 110 pods per server.
- Kubernetes, kernel, and network limitations prevent having too many pods per server. You should maintain a maximum of roughly 24 cores per server and a maximum of the recommended 110 pods per server.

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@jtravee jtravee Mar 8, 2022 •
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@Tejeev, checking that minimum should be maximum here?

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yes, though these are somewhat softer than I think I make it sound. Folks that know what they are doing may up the pod count to the real limit of 251 (IIRC. we should double check that) and there are use cases that might use more cores, per pod, though at the moment they are rare. Not sure how to convey this a bit better or if we leave it as is to prevent over committing by folks that do not have real need of increased limits

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Perhaps:
"It is recommended to maintain a maximum of roughly 24 cores and 110 pods per server"


- If you are deploying an application or system that specifically requires a large number of pods, you may increase the pod limit. Please note, however, that going above 254 pods per server is not supported by default pod CIDR settings unless the pods are using host networking.
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This goes against upstream docs best practice: "No more than 110 pods per node": https://kubernetes.io/docs/setup/best-practices/cluster-large/

Also saying "you may increase the pod limi" implies that this is supported, and we have not tested this in our scaling tests, we do not want to give this impression.


- Even when deploying small workloads, it is recommended that you use a virtualization layer to facilitate less downtime and shorter reboots during upgrades and failures.

For additional hardware recommendations for large Kubernetes clusters and nodes, refer to the official Kubernetes documentation on [building large clusters](https://kubernetes.io/docs/setup/best-practices/cluster-large/).

### Etcd Clusters

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