Integration of Microservices
What is microservice
- is relatively small
- can be developed and deployed independently
- Ideally, each service should have only a small set of responsibilities (SRP)
- Opposite to monolithic application
MOSi, POSi, Weather API, Warning text service, ....
Monolith is evil and only right way is microservice, which is one process written in any language.
Monolith advantages
- One change in one commit
- Easier to test functionality
- No compatibility issues and dependencies
- Deployment and rollback is simple
Integration
- Direct client-to-microservice communication
- API Gateway (Facade)
- Service discovery
- Database per service
- Events sourcing
- Deployment
Direct client to microservice communication
Pro
- Easy to implement
Cons
- Only HTTP protocol
- Too many connections - slow
- Difficult to refactor microservices - merging, splitting
API Gateway
Pros
- encapsulate internal structure
- simplify client code
- auth, cache
Cons
- another component
- development bottleneck
Types
- One for all clients
- One for mobile, one for desktop, one for web
MeteoGroup
- RoadMaster - Backed for Frontend
- Weather API (access to MOSi, POSi)
Service discovery
- Client side service discovery
Service Discovery
Client
Service
- Server side service discovery
Service Discovery
Load Balancer
Service
Client
Service discovery in MG
Service Discovery
(Consul)
Load Balancer
Service A
Client
Service A
manifest.toml
manifest.toml
Database per service
Service A
Database
MySQL
Service B
Database
MongoDB
Pros
- Loosely coupled
- Best suited database for every service
Cons
- Business transactions are harder to implement
- Joining data is challenging
- Complexity - managing SQL and NonSQL databases
"Database per service" doesn't mean a database SERVER per service
Event sourcing
Rather than persisting an object in its current state, event sourcing instead writes an immutable log of deltas (domain events) to the database
App
Event
Event
Event Store
Materialized View
Event
Event
External
Systems
Deployment
Multiple services per Host
Service per Host
Host
Service A
Service B
Service C
Service per VM
VM
Service A
VM
Service B
Service per Container
Container
Service A
Container
Service B
Host
Deployment in MG
Service per Container
Container
Service A
Container
Service A
Docker Host
Container
Service B
-
Marathon
- Check app (running, stopped)
-
Grafana
- Check resources (cpu, memory, ...)
-
Kibana
- Check application logs