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Chapter 2. Getting Started with Spring Boot

2.1. Overview of the circuit breaker booster
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The Netflix/Hystrix circuit breaker enables distributed applications to cope with interruptions to network connectivity and temporary unavailability of backend services. The basic idea of the circuit breaker pattern is that the loss of a dependent service is detected automatically and an alternative behavior can be programmed, in case the backend service is temporarily unavailable.

The Fuse circuit breaker booster consists of two related services:

  • A name service, the backend service that returns a name to greet.
  • A greetings service, the frontend service that invokes the name service to get a name and then returns the string, Hello, NAME.

In this booster demonstration, the Hystrix circuit breaker is inserted between the greetings service and the name service. If the backend name service becomes unavailable, the greetings service can fall back to an alternative behavior and respond to the client immediately, instead of being blocked while it waits for the name service to restart.

2.2. Prerequisites
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To build and run the booster demonstration, install the following prerequisites:

2.3. Generate the booster project
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To generate the circuit breaker booster project, perform the following steps:

  1. Navigate to https://developers.redhat.com/launch.

  2. Click START.

    The launcher wizard prompts you to log in to your Red Hat account.

  3. Click the Log in or register button and then log in.
  4. On the Launcher page, click the Deploy an Example Application button.
  5. On the Create Example Application page, type the name, fuse-circuit-breaker, in the Create Example Application as field.
  6. Click Select an Example.

  7. In the Example dialog, select the Circuit Breaker option. A Select a Runtime dropdown menu appears.

    1. From the Select a Runtime dropdown, select Fuse.
    2. From the version dropdown menu, select 7.3.0 (Red Hat Fuse) (do not select the 2.21.2 (Community) version).
    3. Click Save.
  8. On the Create Example Application page, click Download.
  9. When you see the Your Application is Ready dialog, click Download.zip. Your browser downloads the generated booster project (packaged as a ZIP file).
  10. Use an archive utility to extract the generated project to a convenient location on your local file system.

2.4. Build and run the booster
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To build and run the booster project, perform the following steps:

  1. Open a shell prompt and build the project from the command line, using Maven: 

    cd fuse-circuit-breaker
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    mvn clean package
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    After Maven builds the project, it displays a Build Success message.

  2. Open a new shell prompt and start the name service, as follows: 

    cd name-service
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    mvn spring-boot:run -DskipTests -Dserver.port=8081
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    As Spring Boot starts up, you should see output similar to the following: 

    ...
2019-05-06 20:19:59.401  INFO 9553 --- [           main] o.a.camel.spring.SpringCamelContext      : Route: route1 started and consuming from: servlet:/name?httpMethodRestrict=GET
2019-05-06 20:19:59.402  INFO 9553 --- [           main] o.a.camel.spring.SpringCamelContext      : Total 1 routes, of which 1 are started
2019-05-06 20:19:59.403  INFO 9553 --- [           main] o.a.camel.spring.SpringCamelContext      : Apache Camel 2.21.0.fuse-730078-redhat-00001 (CamelContext: camel-1) started in 0.287 seconds
2019-05-06 20:19:59.406  INFO 9553 --- [           main] o.a.c.c.s.CamelHttpTransportServlet      : Initialized CamelHttpTransportServlet[name=CamelServlet, contextPath=]
2019-05-06 20:19:59.473  INFO 9553 --- [           main] b.c.e.u.UndertowEmbeddedServletContainer : Undertow started on port(s) 8081 (http)
2019-05-06 20:19:59.479  INFO 9553 --- [           main] com.redhat.fuse.boosters.cb.Application  : Started Application in 5.485 seconds (JVM running for 9.841)
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  3. Open a new shell prompt and start the greetings service, as follows: 

    cd greetings-service
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    mvn spring-boot:run -DskipTests
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    As Spring Boot starts up, you should see output similar to the following: 

    ...
2019-05-06 20:22:19.051  INFO 9729 --- [           main] o.a.c.c.s.CamelHttpTransportServlet      : Initialized CamelHttpTransportServlet[name=CamelServlet, contextPath=]
2019-05-06 20:22:19.115  INFO 9729 --- [           main] b.c.e.u.UndertowEmbeddedServletContainer : Undertow started on port(s) 8080 (http)
2019-05-06 20:22:19.123  INFO 9729 --- [           main] com.redhat.fuse.boosters.cb.Application  : Started Application in 7.68 seconds (JVM running for 12.66)
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    The greetings service exposes a REST endpoint at the http://localhost:8080/camel/greetings URL.

  4. Invoke the REST endpoint by either opening the URL in a web browser or by opening another shell prompt and typing the following curl command: 

    curl http://localhost:8080/camel/greetings
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    Here is the response: 

    {"greetings":"Hello, Jacopo"}
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  5. To demonstrate the circuit breaker functionality provided by Camel Hystrix, kill the backend name service by typing Ctrl-C in the shell prompt window where the name service is running.

    Now that the name service is unavailable, the circuit breaker kicks in to prevent the greetings service from hanging when it is invoked.

  6. Invoke the greetings REST endpoint by either opening http://localhost:8080/camel/greetings in a web browser or by typing the following curl command in another shell prompt window: 

    curl http://localhost:8080/camel/greetings
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    Here is the response: 

    {"greetings":"Hello, default fallback"}
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    In the window where the greetings service is running, the log shows the following sequence of messages: 

    2019-05-06 20:24:16.952  INFO 9729 --- [-CamelHystrix-2] route2                                   :  Try to call name Service
2019-05-06 20:24:16.956  INFO 9729 --- [-CamelHystrix-2] o.a.c.httpclient.HttpMethodDirector      : I/O exception (java.net.ConnectException) caught when processing request: Connection refused (Connection refused)
2019-05-06 20:24:16.956  INFO 9729 --- [-CamelHystrix-2] o.a.c.httpclient.HttpMethodDirector      : Retrying request
2019-05-06 20:24:16.957  INFO 9729 --- [-CamelHystrix-2] o.a.c.httpclient.HttpMethodDirector      : I/O exception (java.net.ConnectException) caught when processing request: Connection refused (Connection refused)
2019-05-06 20:24:16.957  INFO 9729 --- [-CamelHystrix-2] o.a.c.httpclient.HttpMethodDirector      : Retrying request
2019-05-06 20:24:16.957  INFO 9729 --- [-CamelHystrix-2] o.a.c.httpclient.HttpMethodDirector      : I/O exception (java.net.ConnectException) caught when processing request: Connection refused (Connection refused)
2019-05-06 20:24:16.957  INFO 9729 --- [-CamelHystrix-2] o.a.c.httpclient.HttpMethodDirector      : Retrying request
2019-05-06 20:24:16.964  INFO 9729 --- [-CamelHystrix-2] route2                                   :  We are falling back!!!!
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  7. For more information about this example, open the Circuit Breaker - Red Hat Fuse page at http://localhost:8080/ (while the greetings-service is running). This page includes a link to the Hystrix dashboard that monitors the state of the circuit breaker.
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