Principles of Microservices

Model Around Business Concept

• More stable than interface structured around technical concepts.
• Reflect change in business process easily.
• Use bounded contexts to define potential domain bounderies.

Culture of Automation

• Keep the added complexity of microservices under control.
• Automated testing is essential.
• Deploy the same way everywhere.
• Use environment definitions.
• Creation of fully automated immutable servers.

Hide Internal Implementation Details

• Technology agnostic API such as REST.
• Services hide and don't share their respective database.
• Use data pumps or event data pumps to consolidate data for reports.

Independently Deployable

• Coexist versionned endpoints: consumers decide when they update themselves.
• One service per host: eliminate impacts on unrelated service.
• Blue/green or canary release: reduce risk of wrong release.
• Consumer-driven contracts: catch breaking changes before they happen.

Isolate Failure

• Don't treat remote call like local calls.
• Plan for failure: Expect that failure will occur anywhere and everywhere.
• Use appropriate timeouts.
• Bulkheads and circuit breakers: limit the fallout of a failing components.
• Sacrifice availability or consistency when network partition is unavailable.

Highly Observable

• Logs aggregation with drill down capabilities.
• Stats aggregation with drill down capabilities.
• Use correlation IDS to trace calls through the system.
• Use semantic monitoring with syntetic transactions injection to simulate real-user behaviors.

Decentralize All The Things
Organization: delegate decision making and control to the team.

• Self-service: develop, test and deploy without relying on other teams.
• Team own their services and are the domain expert.
• Align team to the organization. (Conway's law).
• Internal open source: Use open-source method to run projects.
• Shared governance: people from each service team collectively share responsability for the technical vision of the overall system. 

Architecture: keep associated logic and data within service boundaries.

• Avoid enterprise service bus, orchestration systems, dumb services.
• Prefer choreography over orchestration.
• Prefer dumb middleware with smart endpoints. 

Reference: Newman, Sam. Building Microservice. O'Reilly, 2015.