What is the difference between Azure App Service, Azure Functions, Container Apps and AKS?

Four ways to run application code, differing in abstraction level and control.

• App Service — managed hosting for web applications and APIs. You deploy code or a container; Azure handles the OS, patching, scaling, and load balancing. Deployment slots give you staged releases and swap-based rollback. Use it for a standard web application or API — it is the right default and people over-engineer past it constantly.
• Azure Functions — event-driven serverless. Code runs in response to a trigger — HTTP, a queue message, a timer, a blob upload — and on the Consumption plan you pay only for execution and scale to zero. Use it for intermittent, event-driven, short-lived work. Watch for cold starts on latency-sensitive paths.
• Container Apps — serverless containers built on Kubernetes and KEDA, without exposing Kubernetes. Scale to zero, revisions, traffic splitting, and Dapr integration. Use it for microservices and background workers where you want containers but not cluster management.
• AKS — managed Kubernetes. Maximum control and portability, and maximum operational burden: upgrades, node pools, networking, and monitoring are all yours.

How to choose: pick the highest level of abstraction that meets the requirement. AKS is justified by genuine need for Kubernetes-specific capability or an existing Kubernetes estate — not by a preference for containers.