API Gateway vs Service Mesh - Which One Do You Need

Modern software systems rarely live in isolation. Most applications today are stitched together from dozens,  sometimes hundreds, of independently deployed services, each handling a piece of the puzzle. This helps create smaller units of responsibility and loose coupling. However, the flexibility comes with a new kind of complexity, especially around how these services communicate.

In a monolith, in-process function calls stitch components together. In a service-based world, everything talks over the network. Suddenly, concerns that were once handled inside the application, like retries, authentication, rate limiting, encryption, and observability, become distributed concerns. And distributed concerns are harder to get right.

To manage this complexity, engineering teams typically reach for one of two patterns: the API gateway or the service mesh. 

Both aim to make communication between services more manageable, secure, and observable. But they do it in very different ways, and for different reasons. The confusion often starts when these tools are treated as interchangeable or when their roles are reduced to simple traffic direction: "API gateways are for north-south traffic, service meshes are for east-west." That shortcut oversimplifies both and sets teams up for misuse or unnecessary overhead.

In this article, we look at both API Gateways and Service Mesh in detail, along with their key differences and usage goals.

What is an API Gateway?