Architecting for Scale, 2nd Edition

Chapter 4. Services and Data

As you build and migrate your application to a service-based architecture, it is critically important to be mindful of where you store data and state within your application.

Stateless Services—Services Without Data

Stateless services are services that manage no data and no state of their own. The entire state and all data that the service requires to perform its actions is passed in (or referenced) in the request sent to the service.

Stateless services offer a huge advantage for scaling. Because they are stateless, it is usually an easy matter to add additional server capacity to a service in order to scale it to a larger capacity, both vertically and horizontally. You get maximum flexibility in how and when you can scale your service if your service does not maintain state.

Additionally, certain caching techniques on the frontend of the service become possible if the cache does not need to concern itself with service state. This caching lets you handle higher scaling requirements with fewer resources.

Not all services can be made stateless, obviously, but for those services that can be stateless, it is a huge advantage for scalability.

Stateful Services—Services with Data

When you do need to store data, given what we just discussed in the preceding section, it might seem obvious to store data in as few services and systems as possible. It might make sense to keep all of your data close to one another to reduce the footprint of the services that ...