Sidecar, Ambassador, and Adapter Patterns

Every Pod you deploy into an Istio service mesh gets a second container injected automatically. A MutatingWebhookConfiguration intercepts the Pod creation, patches in an Envoy proxy, and your application never knows it's there. That's the sidecar pattern at work, and it's one of three multi-container designs the CKAD expects you to understand.

"Understand multi-container Pod design patterns (e.g. sidecar, init and others)" is an explicit competency under Application Design and Build (20%). The exam tests your ability to add containers to a Pod spec, wire them together with shared volumes and localhost networking, and debug them with kubectl logs -c. The three classic patterns, sidecar, ambassador, and adapter, each solve a different problem with the same underlying Pod primitive.