This document discusses various aspects of microservices architecture including decomposition, data management, deployment, testing, observability, communication, security, and user interfaces. It recommends decomposing monolithic applications by business capability or subdomain, having a separate database per service, deploying single services on containers or VMs, implementing service integration contract testing and component testing in isolation, and using centralized logging, monitoring, and tracing. It also covers API gateways, service discovery, asynchronous messaging vs RPC-style communication, circuit breakers, cross-cutting concerns, and passing access tokens from gateways to services.

1. Microservices
vol.1.2.9
by Tomasz Tomczyk

3. Monolit -> Microservices

4. Decomposition
● Decompose by business capability
○ A business capability often corresponds to a business object, e.g.
■ product module -> product service
■ order module -> order service
● Decompose by subdomain
○ Define services corresponding to DDD subdomains. microservices.io

5. Data
● Database per Service
○ Event-driven architecture
○ Saga pattern
microservices.io

6. Deployment
● Multiple Services per host
● Single Service per host
○ Service per Container
○ Service per VM
microservices.io

7. Testing
● Service Integration Contract Test
○ Consumer knows:
■ what endpoints can use
■ what input do the endpoints take
■ what does the output look like.
● Service Component Test
○ Test a service in isolation. microservices.io

8. Observability
● Logging
○ centralized
○ not only errors (e.g. user activities)
● Monitoring
○ centralized
○ push/pull systems
● Tracing
○ unique request identity
● Visualization

9. Communication
Other system try to communicate with
microservice
● Directly connecting the front-end to
the microservices
● API gateway
○ BFF
○ protocol translations
unikow.github.io

10. Communication - Discovery
● Service registry
○ self registration
○ 3rd party registration
● Examples
○ Eureka - Netflix (sr),
Apache Zookeeper, Consul
auth0.com
auth0.com

11. Communication - Discovery
Network locations of the services are not
fixed.
● Client-side discovery
○ use smart HTTP client
● Server-side discovery
○ API Gateway (Router)
○ clear HTTP client
auth0.com
auth0.com

12. Communication - Style
Communication between our microservices
● Messaging (asynchronous)
● Remote Procedure Invocation (synchronous)

13. Communication - Circuit Breaker
Errors when one service is
unavailable
On failure strategy
● return default/cached data
● return error to caller
callistaenterprise.se

14. Cross-cutting concerns
● Microservice Chassis
● Externalized configuration
apprize.info

15. Security
● Access Token
○ The API Gateway authenticates the request
and passes an access token (e.g. JSON Web
Token)
microservices.io

16. UI
● Server-side page fragment composition
○ return rendered view parts
● Client-side UI composition
○ return response asjson
microservices.io

18. End ...