In this question the accepted answer shows how to have multiple deployments in a single service so they can talk to each other using their internal loadbalancer ports. What are the pros and cons? My guesses:
Pros:
Cons:
The only common reason to have multiple deployments in one service is for blue/green stuff, or maybe canary deploys (though usually that's done via a proxy with better control over the canary scaling factors). Beyond that, it comes up pretty rarely, sometimes maybe for integrating with Prometheus Operator's ServiceMonitor, or very niche tricks with in-place system rewrites.