Route webhook to all replicas Normally a request gets routed to one of the replicas.  However, if each instance need to take some action when a webhook request comes in, how can I route the request to all replicas?

Obviously only one instance can reply, so I am skeptical if this is possible.

Alternatively, is there a way for when one of the instances receives the request, to communicate it to the others?
This is something you'd have to build. Kubernetes doesn't natively offer this as a pattern.

There are a few approached you can take, but a common on is to use a queue that has this functionality. I'd suggest starting with Nats because it's a CNCF project that is easy to run natively in Kubernetes. When one of your replicas receives the request, it can post a message to the queue that can deliver the message to every subscriber.