Java + .NET in Docker & Kubernetes: 3 Architecture Patterns That Actually Work

If you've ever tried to deploy a system where Java and .NET need to talk to each other inside containers, you know the pain. Do you cram both runtimes into one image? Split them into sidecars? Go full microservices with gRPC? I've been working through each of these approaches for a polyglot trading platform, and there are real trade-offs that most "just use Kubernetes" advice glosses over. Here's what I've learned — with actual Dockerfiles and K8s manifests you can steal. Why Containerize Java/.NET Integration at All? Before the how — the why: Environment parity: Java and .NET versions, runtime configs, and native dependencies are locked into the image. No more "works on my machine" across the JVM and CLR. Independent scaling: Java and .NET components scale independently — critical when one side is compute-heavy and the other is I/O-bound. Resource isolation: Kubernetes resource limits prevent a misbehaving JVM from starving the .NET runtime (or vice versa). Cloud portability: Same ima