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Re: NetworkCIDR for big cluster



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:

Hi

 

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

 

Questions:

 

1.       

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

 

  clusterNetworkCIDR: 10.1.0.0/16

  serviceNetworkCIDR: 172.30.0.0/16

 

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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