A new Kubernetes Deployment with 2+ replicas for high availability.
I want to be able to execute a command on the first pod only, let's say create a DB, and let the other replicas wait for the first one to complete.
To implement this, I just want to know in the pod if this is replica #1 or not.
So in the pod's entry point I can test:
if [ $REPLICA_ID -eq 1 ]; then
CreateDB
else
WaitForDB
fiCan this be done in Kubernetes?
in Kubernetes a Deployment is considered stateless and therefore doesn't provide the feature you're looking for. You should rather look into StatefulSet and their features.
A StatefulSete.g. supports ordered creation and when combined with the generally available readinessProbe for you pods you could create the desired behaviour. Also the pod name is stable within a StatefulSet so your test could then be done with the hostname of the Pod.
Instead of the accepted answer, wouldn't an init container fit your problem description better?
Add some kind of semaphore system (if needed) to ensure it is executed correctly?