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Re: NetworkCIDR for big cluster

Pod limits are now directly settable, so no longer hard coded.

It sounds like you would plan for 100k pods which a 15 or 14 cidr for pods would cover.  I would recommend leaving some headroom there.  14 might be safer if in the future you want to continue to grow the cluster - our target max cluster size is ~ 300k pods, so if you expect a significant bump plan for 14 ahead of time.

In practice, most large clusters will be dense, and be dense due to services.  I would plan for 1 pod per service just to be safe, so match the cidr from pods.

There are multi tenant network settings that might impact how many pods per node are available that I think default for >>100 pods per node, but please double check.

On Oct 6, 2016, at 5:24 PM, Srinivas Naga Kotaru (skotaru) <skotaru cisco com> wrote:

Yes, we are using multi-tenant SDN plugin and our nodes are 8cpu x 64 GB capacity.  Planning to host more than 100 pods per node. With the latest OpenShift release, I hope we don’t have old hard limits on cluster size and # pods on per node


I don’t have an accurate answer for # services per project, which we can’t control at platform side.


Based on abov facts can you recommend a decent CIDR for pods & service?



Srinivas Kotaru


From: "ccoleman redhat com" <ccoleman redhat com>
Date: Thursday, October 6, 2016 at 1:50 PM
To: Srinivas Naga Kotaru <skotaru cisco com>
Cc: dev <dev lists openshift redhat com>
Subject: Re: NetworkCIDR for big cluster



On Oct 6, 2016, at 1:23 PM, Srinivas Naga Kotaru (skotaru) <skotaru cisco com> wrote:



We ‘re building 3 big clusters, 1 specific to each data center. growth  expected to 1000 nodes each cluster over the time.





# egrep 'clusterNetworkCIDR|serviceNetworkCIDR' /etc/origin/master/master-config.yaml





above are default subnet values.  These defaults will be sufficient for 1k clsuter size?


That would be 64k pods and services.  If you expect densities in excess of 100 pods per node you should probably plan for a larger cidr for the cluster network and if you are using the multi tenant plugin you'll also want to plan around how many unique projects you will have.


So inputs are:

# of projects

Expected number of services per project (simple apps or complex apps per project)

Expected pod densities per node




2.      if answer is ‘no’ can we change once cluster is build with new CIDR values depending on growth? ( I heard it is not possible once cluster was build)



It is possible to grow it if you include the original cidr in the expanded cidr.  However, it can be disruptive so we recommend planning up front.  I would recommend leaving the possibility of a larger block open by expanding the mask if you are unsure about exact limits.



3.      if answer is ‘no’ what is the right CIDR’s for 1k cluster size?




Srinivas Kotaru

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