Cloud Native Java Workshop

The accompanying code for this workshop is on Github

Setup

microservices, for better or for worse, involve a lot of moving parts. Let's make sure we can run all those things in this lab.

• You will need JDK 8, Maven, an IDE and Docker in order to follow along. Specify important environment variables before opening any IDEs: JAVA_HOME.
• Go to the Spring Initializr and specify the latest milestone of Spring Boot 1.3 and then choose EVERY checkbox except those related to AWS or Consul, then click generate. In the shell, run mvn -DskipTests=true clean install to force the resolution of all those dependencies so you're not stalled later. Then, run mvn clean install to force the resolution of the test scoped dependencies. You may discard this project after you've installed everything.

(Some versions of this workshop will not use Docker)

1. "Bootcamp"

In this lab we'll take a look at building a basic Spring Boot application that uses JPA and Spring Data REST. We'll look at how to start a new project, how Spring Boot exposes functionality, and how testing works.

• Go to the Spring Initializr and select H2, REST Repositories, JPA, Vaadin, Web. Select the latest Spring Boot 1.3.x version. give it an artifactId of reservation-service.
• Run mvn clean install and import it into your favorite IDE using Maven import.
• Add a simple entity (Reservation) and a repository (ReservationRepository)
• Map the repository to the web by adding org.springframework.boot:spring-boot-starter-data-rest and then annotating the repository with @RepositoryRestResource
• Add custom Hypermedia links
• Write a simple unit test

Questions:

• What is Spring? Spring, fundamentally, is a dependency injection container. This detail is unimportant. What is important is that once Spring is aware of all the objects - beans - in an application, it can provide services to them to support different use cases like persistence, web services, web applications, messaging and integration, etc.
• Why .jars and not .wars? We've found that many organizations deploy only one, not many, application to one Tomcat/Jetty/whatever. They need to configure things like SSL, or GZIP compression, so they end up doing that in the container itself and - because they don't want the versioned configuration for the server to drift out of sync with the code, they end up version controlling the application server artifacts as well as the application itself! This implies a needless barrier between dev and ops which we struggle in every other place to remove.
• How do I access the by-name search endpoint? Follow the links! visit http://localhost:8080/reservations and scroll down and you'll see links that connect you to related resources. You'll see one for search. Follow it, find the relevant finder method, and then follow its link.

3. The Config Server

The 12 Factor manifesto speaks about externalizing that which changes from one environment to another - hosts, locators, passwords, etc. - from the application itself. Spring Boot readily supports this pattern, but it's not enough. In this lab, we'll loko at how to centralize, externalize, and dynamically update application configuration with the Spring Cloud Config Server.

• Go to the Spring Initializr, choose the latest milestone of Spring Boot 1.3.x, specify an artifactId of config-service and add Config Server from the list of dependencies.
• You should git clone the Git repository for this workshop - https://github.com/joshlong/bootiful-microservices-config
• In the Config Server's application.properties, specify that it should run on port 8888 (server.port=8888) and that it should manage the Git repository of configuration that lives in the root directory of the git clone'd configuration. (spring.cloud.config.server.git.uri=...).
• Add @EnableConfigServer to the config-service DemoApplication
• Add server.port=8888 to the application.properties to ensure that the Config Server is running on the right port for service to find it.
• Add the Spring Cloud BOM (you can copy it from the Config Server) to the reservation-service.

We will need to modify the reservation-service's pom.xml in order to make it a config client. To do this, add the following to your pom.xml of the reservation-service from step #1.

Example:

<dependencyManagement>
    <dependencies>
      ...
      <dependency>
        <groupId>org.springframework.cloud</groupId>
        <artifactId>spring-cloud-dependencies</artifactId>
        <version>Brixton.RELEASE</version>
        <type>pom</type>
        <scope>import</scope>
      </dependency>
    </dependencies>
</dependencyManagement>

IMPORTANT: Make sure that you make this modification in the </dependencyManagement> block. There are two places where Maven dependencies are added in a pom.xml and some people tend to get confused at this step. If you need help, please raise your hand and flag down an instructor.

Next, add org.springframework.cloud:spring-cloud-starter-config to the reservation-service. We'll add this dependency declaration to the general dependencies tag, unlike the previous modification to </dependencyManagement>.

Example:

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

Next:

Create a boostrap.properties that lives in the same place as application.properties and discard the application.properties file. Now we need only to tell the Spring application where to find the Config Server, with the property spring.cloud.config.uri=${config.server:http://localhost:8888}, and how to identify itself to the Config Server and other services, later, with spring.application.name.

Now, run the Config Server:

We'll copy and paste bootstrap.properties for each subsequent module, changing only the spring.application.name as appropriate.

In the reservation-service, create a MessageRestController and annotate it with @RefreshScope. Inject the ${message} key and expose it as a REST endpoint, /message.

Trigger a refresh of the message using the /refresh endpoint.

EXTRA CREDIT: Install RabbitMQ server and connect the microservice to the event bus by adding the org.springframework.cloud:spring-cloud-starter-bus-amqp then triggering the refresh using the /bus/refresh.

4. Service Registration and Discovery

In the cloud, applications live and die as capacity dictates, they're ephemeral. Applications should not be coupled to the physical location of other services as this state is fleeting. Indeed, even if it were fixed, services may quickly become overwhelmed, so it's very handy to be able to specify how to load balance among the available instances or indeed ask the system to verify that there are instances at all. In this lab, we'll look at the low-level DiscoveryClient abstraction at the heart of Spring Cloud's service registration and discovery support.

• Go to the Spring Initializr, select the Eureka Server (this brings in org.springframework.cloud:spring-cloud-starter-eureka-server) checkbox, name it eureka-service and then add @EnableEurekaServer to the DemoApplication class.
• Make sure this module also talks to the Config Server as described in the last lab by adding the org.springframework.cloud:spring-cloud-starter-config.
• add org.springframework.cloud:spring-cloud-starter-eureka to the reservation-service
• Add @EnableDiscoveryClient to the reservation-service's DemoApplication and restart the process, and then confirm its appearance in the Eureka Server at http://localhost:8761
• Demonstrate using the DiscoveryClient API
• Use the Spring Initializr, setup a new module, reservation-client, that uses the Config Server (org.springframework.cloud:spring-cloud-starter-config), Eureka Discovery (org.springframework.cloud:spring-cloud-starter-eureka), and Web (org.springframework.boot:spring-boot-starter-web).
• Create a bootstrap.properties, just as with the other modules, but name this one reservation-client.
• Create a CommandLineRunner that uses the DiscoveryClient to look up other services programmatically

EXTRA CREDIT: Install Consul and replace Eureka with Consul. You could use ./bin/consul.sh, but prepare yourself for some confusion around host resolution if you're running Docker inside a Vagrant VM.

5. Edge Services: API gateways (circuit breakers, client-side load balancing)

Edge services sit as intermediaries between the clients (smart phones, HTML5 applications, etc) and the service. An edge service is a logical place to insert any client-specific requirements (security, API translation, protocol translation) and keep the mid-tier services free of this burdensome logic (as well as free from associated redeploys!)

Proxy requests from an edge-service to mid-tier services with a microproxy. For some classes of clients, a microproxy and security (HTTPS, authentication) might be enough.

• Add org.springframework.cloud:spring-cloud-starter-zuul and @EnableZuulProxy to the reservation-client, then run it.
• Launch a browser and visit the reservation-client at http://localhost:9999/reservation-service/reservations. This is proxying your request to http://localhost:8000/reservations.

API gateways are used whenever a client - like a mobile phone or HTML5 client - requires API translation. Perhaps the client requires coarser grained payloads, or transformed views on the data

• In the reservation-service, create a client side DTO - named Reservation, perhaps? - to hold the Reservation data from the service. Do this to avoid being coupled between client and service
• Add org.springframework.boot:spring-boot-starter-hateoas
• Add a REST service called ReservationApiGatewayRestController that uses the @Autowired @LoadBalanced RestTemplate rt to make a load-balanced call to a service in the registry using Ribbon.
• Map the controller itself to /reservations and then create a new controller handler method, getReservationNames, that's mapped to /names.
• In the getReservationNames handler, make a call to http://reservation-service/reservations using the RestTemplate#exchange method, specifying the return value with a ParameterizedTypeReference<Resources<Reservation>>> as the final argument to the RestTemplate#exchange method.
• Take the results of the call and map them from Reservation to Reservation#getReservationName. Then, confirm that http://localhost:9999/reservations/names returns the names.

The code works, but it assumes that the reservation-service will always be up and responding to requests. We need to be a bit more defensive in any code that clients will connect to. We'll use a circuit-breaker to ensure that the reservation-client does something useful as a fallback when it can't connect to the reservation-service.

• Add org.springframework.boot:spring-boot-starter-actuator and org.springframework.cloud:spring-cloud-starter-hystrix to the reservation-client
• Add @EnableCircuitBreaker to our DemoApplication configuration class
• Add @HystrixCommand around any potentially shaky service-to-service calls, like getReservationNames, specifying a fallback method that returns an empty collection.
• Test that everything works by killing the reservation-service and revisiting the /reservations/names endpoint
• Go to the Spring Initializr and stand up a new service - with an artifactId of hystrix-dashboard - that uses Eureka Discovery, Config Client, and the Hystrix Dashboard.
• Identify it is as hystrix-dashboard in bootstrap.properties and point it to config server.
• Annotate it with @EnableHystrixDashboard and run it. You should be able to load it at http://localhost:8010/hystrix.html. It will expect a heartbeat stream from any of the services with a circuit breaker in them. Give it the address from the reservation-client: http://localhost:9999/hystrix.stream