Spring Cloud Demo

Demonstration of microservices using spring boot and spring cloud.

The intention of this project is to demonstrate how to setup a system based on microservices. The definition of microservices is not discussed here, only the tools provided by spring cloud that support aspects as described with the The Twelve-Factor App.

Phase 1: Microservices

With the first the microservices used for the demonstration are developed. The microservices only serve as demonstration, thus no real functionality is provided. These services form a simple calulator, where each service provides a single arithmetic function, thereby exaggerating the 'Single Responsibility Principle':

• Addition service;
• Deduction service;
• Multiplication service;
• Division service;
• Fibonacci service;

The latter delegates part of its implementation to the Addition service.

Phase 2: Introducing the Configuration service

Steps for the configuration service

• Using Spring Initializr, with the options Config Server and Actuator enabled, to generate a starter project.
• Rename the generated application.properties to bootstrap.yml.
• Change the property definitions to yaml format.
• Create a git repository on the local file system.
• Add the following to the bootstrap.yml:

spring:
  cloud:
    config:
      server:
        git:
          uri: file://<localtion of the git repo>

Steps for the configuration clients

• Add the following dependencies to the pom for each component:
  • org.springframework.boot:spring-boot-starter-actuator
  • org.springframework.cloud:spring-cloud-config-client
• Rename the application.properties to bootstrap.yml
• Add the following to each components bootstrap.yml:

spring:
  application:
    name: <component identifier>
  cloud:
    config:
      url: <url to the running config server>
server.port: <component port number>

• Create another config file named application.yml, needed to expose the refresh endpoint, with the content:

# Expose the management endpoints
management:
  endpoints:
    web:
      exposure:
        include: *

• Add the @RefreshScope for each controller with configuration properties that need to change dynamically:

@RefreshScope
@RestController
@RequestMapping(value = "/fibonacci", produces = MediaType.APPLICATION_JSON_UTF8_VALUE)

Phase 3: Add monitoring

See Spring Boot Admin on github and this descriptive tutorial on Vojtech Ruzicka's Programming Blog. There's also a somewhat outdated instruction written on Eugen Baeldung's website.

The Spring Boot Admin Application consists of a server component and a client component. First we will setup the server component and add it to calculator suite:

• Create a new Spring Boot project named AdminServer;
• Open the generated AdminServerApplication class and add the annotation @EnableAdminServer at class level. That's it for the admin server.

Make the following changes on each client that needs to be monitored:

• Add the dependency to the pom:

<dependency>
    <groupId>de.codecentric</groupId>
    <artifactId>spring-boot-admin-starter-client</artifactId>
    <version>2.1.0</version>
</dependency>

• Define the URL where the admin server is running to the bootstrap.yml spring.boot.admin.client.url=http://localhost:8080.

Phase 4: Using OpenFeign client

Feign is a library created by Netlix and donated to spring-cloud. Feign provides an abstraction over REST service calls. With Spring Cloud Feign developers only need to write an interface to describing the client interface, while Spring CLoud Feign dynamically provisions the implementation at runtime.

This demo only has a single inter service communication between the FibonacciService and the AdditionService.

Make the following changes:

• Add these entries to pom:

        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-openfeign</artifactId>
        </dependency>

• Define the interface
• Add the @EnableFeignClients annotation to the application class.
• Use the feign client instead of the RestTemplate:

    @Autowired
    public FibonacciController(AdditionServiceProxy additionService) {
        this.additionService = additionService;
    }
    ...
        int nextValue = additionService.add(val, prev);

Phase 5: Load balancing the services using Ribbon

Phase 6: