Kubernetes : How to detect total replicas from within a Java micro service

Question

What I'm trying to solve : Have a Java microservice be aware of total number of Replicas. This replica count is dynamic in nature

Problem: Kubernetes downward API has limited metadata that doesnt include this information. Is there a way to qausi-query a kubectl-like command natively from a container?

Why am I trying to do this: In relation to Kafka, new replica will cause a rebalance. Looking to mitigate rebalancing when new containers come online/offline with additional business logic.

Goal: Create an arbiter java-service that detects replica count for deployment xyz and orchestrates corresponding pods to yield on Kafka connection until criteria is met

also if this is crazy, I wont take offense. In that case I'm asking for a friend

Answer 1

Kubernetes downward API has limited metadata that doesnt include this information. Is there a way to qausi-query a kubectl-like command natively from a container?

You need to query the Kubernetes API server for info about the number of replicas for a specific Deployment. You can do this with kubernetes-client java.

Why am I trying to do this: In relation to Kafka, new replica will cause a rebalance. Looking to mitigate rebalancing when new containers come online/offline with additional business logic.

Sounds like you want consistent number of Pods all the time, e.g. avoiding Rolling Deployment? In your Deployment, you can set strategy: to type: Recreate - then the current Pod will be removed first, and then the new will be created - so at most 1 is running at the same time (or the same number as replicas).

StatefulSet

When you want at most X number of replicas you should consider using StatefulSet as its behavior differ from Deployment when e.g. a Node becomes unreachable. Deployment has the behavior, at least X number of replicas.