Notes

Created during the Master Microservices with Spring Boot and Spring Cloud Udemy course. The course was in Java but this was done in Kotlin because. Tried Kofu (code in kofu branch) but it didn't support JPA so settled for Beans & Router(WebMVC.fn) DSLs and other sugars

• Creating a RESTful resource
• Challenges in Microservices Architecture
• Spring Cloud Config
• Feign
• Ribbon
• Eureka
  • Summary of Feign,Ribbon,Eureka
• Zuul
• Sleuth/Zipkin
• Spring Cloud Bus
• Hystrix

Creating a RESTful resource

• Define entity, Dao and controller
• Define findAll, findById, create, deleteById
• Define custom exceptions
• Define validations for entity and corresponding handler
• Enable actuator endpoints for monitoring
• Misc. things like HATEOAS, Locales, Filtering etc.
• Decide versioning scheme based on factors such as
  • Caching requirement (URI/param based)
  • Ease of Use & Documenting/ Browser friendly (URI/param based)
  • URI Pollution (Header/mime type based)
• Configure basic auth (?)

Challenges in Microservices Architecture

• Bounded context (Separaction of concern, figuring out boundaries)
• Configuration management
• Dynamic scaling
• Visibility / Fault detection
• Domino effect / Fault tolerance

Spring Cloud Config

• Problems Solved:
  • Easier config management for multiple environments
  • Ability to change properties without application restart
• Steps:
  • Server:
    • Create service with spring cloud server dependency
    • Add config git repo uri in server application.properties
    • Commit configs in the added repo as <client-service-id>-<env>.properties
    • Available at <server-host>:<server-port>/<client-service-id>/<env/default>
  • Client:
    • Rename application.properties to bootstrap.properties
    • Add config server uri in bootstrap.properties
    • Specify env as active profile if required
    • Enable actuator refresh endpoint to be able to reload without service restart
• Notes:
  • Config changes must be committed in order to be picked up by the config server

Feign

• Problems solved:
  • Invoking other services
• Steps:
  • Add openfeign dependency
  • Add @EnableFeignClients(<Feign clients package>)
  • Define proxy interface using @FeignClient(name = "service-id", url="url:port")
  • In the interface copy the controllers of service and adjust return type if required
  • Autowire and call method

Ribbon

• Problems solved:
  • Client side load balancing
  • DNS
• Steps:
  • Add netflix-ribbon dependency
  • Add @RibbonClient(name = "<destination-service-id>") (url can now be removed from FeignClient)
  • Add nodes in property file:

  <detination-service-id>.ribbon.listOfServers=http://localhost:777,http://localhost:888
  

Eureka

• Problems solved:
  • Service discovery and registration
• Server:
  • Add eureka server dependency
  • Enable server using @EnableEurekaServer
  • Disable register with eureka & fetch registry in properties (?)
• Clients:
  • Add eureka client dependency
  • Enable discovery using @EnableDiscoveryClient
  • Add service url in properties
  • Restart to register with Eureka
• Integration with Feign & Ribbon:
  • Service id in feign and ribbon
  • Remove ribbon list of servers property

Summary of Feign,Ribbon,Eureka

• Feign: Easy to call with URL
• Ribbon: Calling with multiple URLs
• Eureka: Calling with name instead of URL, adding and removing nodes dynamically

Zuul

• Problems solved:
  • Authentication
  • Rate limit
  • Fault Tolerance (fallback)
  • Service Aggregation (1 call instead of 15 calls)
• Steps:
  • Create server project with zuul dependency
  • Add @EnableZuulProxy
  • Filter:
    • Extend ZuulFilter and override methods
    • Use URI zuul-server-url:port// (Destination Service as well as Zuul should be registered with Eureka)

Sleuth/Zipkin

• Problems solved:
  • Identification of muliple internal requests belonging to same request
  • Centralization and visualization for easy debugging
• Steps:
  • Sleuth:
    • Add dependency in service
    • Add Sampler bean returning Sampler.ALWAYS_SAMPLE
  • Zipkin:
    • Add zipkin-starter and rabbitmq dependencies
    • Start rabbitmq and zipkin servers
    • Start applications

Spring Cloud Bus

• Problems solved:
  • Intercommunication between services (For ex. to refresh config, we'll have to hit 100 endoints for 100 instances)
• Steps:
  • Add dependency in config server and clients
  • Enable bus-refresh endpoint in clients
  • Send a POST request at any client node's /actuator/bus-refresh endpoint

Hystrix

• Problems solved:
  • Prevention of cascading failures (fault tolerance)
• Steps:
  • Add dependency
  • Add @EnableHystrix
  • Fallback:
    • Add @HystrixCommand(fallback=<fallback-method>) on controller method