Microservices

Russell Bateman
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Microservices are (really) small services (or service fragments) that make up a single, purposeful application. Why are microservices so compelling? Summed up in a single expression, it's technical debt. Or, the reduction of it.

Microservices don't care what languages are used in their implementation since the constituent components live and die by their contracted interfaces: each component can do whatever it needs to do in whatever way it wants as long as components interfacing with it can get what the component has agreed to deliver the way it agreed to deliver it.

Testing is simplifed because only the service is tested and not all features of the entire application at once. (Integration testing is still a requirement, but basic testing is much easier to conceive and much cheaper.) Reduction in technical debt.

Debugging is simplifed. If there's a null-pointer exception or other bug, it's not "somewhere inside the whole monolithic mess somewhere." It's probably—identifiably—in one service or between two services, i.e.: service A send data incorrectly to service B or service B bungled the data it got. Reduction in technical debt.

Deployment is easier because when a change to a service is made, only that service needs redeployment (unless a change in its contract with other services was made). Reduction in technical debt.

Strangler pattern

This pattern is used to migrate a monolithic application to a suite of microservices. A service or aspect of a service is chosen for migration, written anew, greenfield or adapted from existing code, but separated out from the monolith yet leaving the monolith version intact and functioning. Traffic is gated through the new component to share the load with the original implementation. Good processes, testing, deployment, etc. characterize the new version. Eventually, traffic through the legacy component can be shut off in favor of using only the new component. This process is repeated (or engaged simultaneously) for other aspects of the monolith until there is no longer any traffic transiting the old application.