Kubernetes job that consists of two pods (that must run on different nodes and communicate with each other)

Question

I am trying to create a Kubernetes job that consists of two pods that have to be scheduled on separate nodes in our Hybrid cluster. Our requirement is that one of the pods runs on a Windows Server node and the other pod is running on a Linux node (thus we cannot just run two Docker containers from the same pod, which I know is possible, but would not work in our scenario). The Linux pod (which you can imagine as a client) will communicate over the network with the Windows pod (which you can imagine as a stateful server) exchanging data while the job runs. When the Linux pod terminates, we want to also terminate the Windows pod. However, if one of the pods fail, then we want to fail both pods (as they are designed to be a single job)

Our current design is to write a K8S service that handles the communication between the pods, and then apply the service and the two pods to the cluster to "emulate" a job. However, this is not ideal since the two pods are not tightly coupled as a single job and adds quite a bit of overhead to manually manage this setup (e.g. when failures or the job, we probably need to manually kill the service and deployment of the Windows pod). Plus we would need to deploy a new service for each "job", as we require the Linux pod to always communicate with the same Windows pod for the duration of the job due to underlying state (thus cannot use a single service for all Windows pods).

Any thoughts on how this could be best achieved on Kubernetes would be much appreciated! Hopefully this scenario is supported natively, and I would not need to resort in this kind of pod-service-pod setup that I described above.

Many thanks

Answer 1

I am trying to distinguish your distaste for creating and wiring the Pods from your distaste at having to do so manually. Because, in theory, a Job that creates Pods is very similar to what you are describing, and would be able to have almost infinite customization for those kinds of rules. With a custom controller like that, one need not create a Service for the client(s) to speak to their server, as the Job could create the server Pod first, obtain its Pod-specific-IP, and feed that to the subsequently created client Pods.

I would expect one could create a Job controller using only bash and either curl or kubectl: generate the json or yaml that describes the situation you wish to have, feed it to the kubernetes API (since the Job would have a service account - just like any other in-cluster container), and use normal traps to cleanup after itself. Without more of the specific edge cases loaded in my head it's hard to say if that's a good idea or not, but I believe it's possible.