EKS EBS and Zones !

Question

Hello,

Can someone please tell me what the reccomendation is for using EBS in EKS in 3 AZ's ? If I have a deployment with 3 replicas should I use topology spread constraints  ? The following article seems to suggest that if I add this property, the scheduler will place a pod in each AZ ?

https://aws.github.io/aws-eks-best-practices/reliability/docs/application/

I'm assuming this means my deployment with 3 replicas will have a volume on each AZ  ? Is this essentially a replicated copy of data accross 3 AZ's so if one AZ goes down, data will still be available in either of the other two AZ's....right ?

Also, what if I already have a deployment with 3 replicas but 2 of the replicas are in the same AZ, if I add topology spread constraints, will this automatically even out so they'll run in sperate AZ's ?

Many thanks in advance !!

Regards,
Johnny

Answer

Topology spread constraints is a good way to ensure that pods does not start in same zone or same host ( based on the constraints definition) However one approach in the usecase could be use to  statefulsets[1].

You are right, if you add topology constraint "topologyKey: "topology.kubernetes.io/zone" it will schedule both the pods in different AZs ( based on AZs defined in the cluster) 
1. https://aws.amazon.com/blogs/containers/running-stateful-workloads-with-amazon-eks-on-aws-fargate-using-amazon-efs/

Answer

Thanks, EFS is not an option - only EBS. These applications are actually statefulsets but how does that guarantee the 3 pods will be spread accross each AZ ? Unfortunatly I don't have an EKS cluster to test at the moment.

EKS EBS and Zones !

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