Microservice Architecture Glossary

A work-in-progress definition of terms that are not expressed as patterns.


A service’s reason for existing. It consists of:


A command is an operation that mutates data.


A component is a software unit that is executabe or deployable. For example, a Java WAR file or executable JAR file; or an operating system executable.

DORA metrics

Developed by the authors of Accelerate, the DORA metrics measure the performance of a software development teams:

  • Deployment frequency - the frequency with which software changes are deployed to production.
  • Lead time for changes - the time it takes to go from commit to deploy.
  • Time to restore service - the time it takes to restore service after a production incident or outage.
  • Change failure rate - the percentage of production deployments that result in a failure or require remediation.

The DORA DevOps Quick Check is a simple five question assessment of how well you are delivering software.

Modular monolith

A variant of the monolithic architecture that is organized around subdomains (e.g. business capabilities) rather than technical layers (e.g. presentation, business logic, persistence).

Monolithic architecture

An architectural style that structures the application as a single executable/deployable component. See the Monolithic architecture pattern for more details.

Microservice architecture

An architectural style that structures at application as set of loosely coupled, independently deployable components (a.k.a. services). See the Microservice architecture pattern for more details.


An operation is an invocable behavior of a service. There are two types of operations: commands and queries. An operation can be invoked by a service client either synchronously or asynchronously. It might also be invoked by the passing of time, e.g. to implement a batch job.


A pattern is a “reusable solution to a problem that occurs in particular context”. Read more


A query is an operation that retrieves data.


Each service is an element of the Microservice Architecture that is:

  • Loosely coupled with other services
  • Independently deployable - it an independently deployable/executable component, such as a WAR file, executable JAR, EAR file, OSGI Bundle, or operating System executable
  • Owned by a small, cross-functional team

A service has an API.

Learn more

System operation

A system operation is an invocable behavior of the application. There are two types of operations: commands and queries. An operation is invoked by an application client - human via UI, or an external application - either synchronously or asynchronously. It might also be invoked by the passing of time, e.g. a batch job that is executed periodically.

In a microservice architecture, a system operation is either local or distributed. A local operation is implemented by a single service. A distributed operation is implemented by multiple collaborating services.


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About is brought to you by Chris Richardson. Experienced software architect, author of POJOs in Action, the creator of the original, and the author of Microservices patterns.

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20 Mar 2024 » A tour of two sagas
21 Dec 2023 » Thoughts about team size
24 Jul 2017 » Revised data patterns