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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 component 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, which returns a name to greet, and
  • A greetings service, which invokes the name service to get a name and then returns the string, Hello, NAME.

In this demonstration, the Hystrix circuit breaker is inserted between the greetings service and the name service. If the name service becomes unavailable, the greetings service can fall back to an alternative behavior and respond to the client immediately, instead of blocking 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. The launcher wizard prompts you to log in to your Red Hat account. Click the Log in or register button to 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 7.1.0 (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. Your browser now commences downloading the generated booster project (packaged as a ZIP file).
  11. After downloading the ZIP file, use an archive utility to extract the generated project to a convenient location on your local filesystem.

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

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

    ...
2019-06-25 09:33:01.444  INFO 11066 --- [           main] o.a.camel.spring.SpringCamelContext      : Route: route1 started and consuming from: servlet:/name?httpMethodRestrict=GET
2019-06-25 09:33:01.445  INFO 11066 --- [           main] o.a.camel.spring.SpringCamelContext      : Total 1 routes, of which 1 are started
2019-06-25 09:33:01.446  INFO 11066 --- [           main] o.a.camel.spring.SpringCamelContext      : Apache Camel 2.21.0.fuse-710018-redhat-00001 (CamelContext: camel-1) started in 0.490 seconds
2019-06-25 09:33:01.460  INFO 11066 --- [           main] o.a.c.c.s.CamelHttpTransportServlet      : Initialized CamelHttpTransportServlet[name=CamelServlet, contextPath=]
2019-06-25 09:33:01.566  INFO 11066 --- [           main] b.c.e.u.UndertowEmbeddedServletContainer : Undertow started on port(s) 8081 (http)
2019-06-25 09:33:01.572  INFO 11066 --- [           main] com.redhat.fuse.boosters.cb.Application  : Started Application in 6.102 seconds (JVM running for 9.772)
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  3. Open a new shell prompt and start the greetings service, as follows: 

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

    ...
2019-06-25 09:35:00.028  INFO 11224 --- [           main] o.a.c.c.s.CamelHttpTransportServlet      : Initialized CamelHttpTransportServlet[name=CamelServlet, contextPath=]
2019-06-25 09:35:00.101  INFO 11224 --- [           main] b.c.e.u.UndertowEmbeddedServletContainer : Undertow started on port(s) 8080 (http)
2019-06-25 09:35:00.108  INFO 11224 --- [           main] com.redhat.fuse.boosters.cb.Application  : Started Application in 7.248 seconds (JVM running for 11.143)
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  4. The greetings service exposes a REST endpoint at the URL, http://localhost:8080/camel/greetings. You can invoke the REST endpoint either from a Web browser or from a shell prompt, using the curl command, as follows: 

    $ curl http://localhost:8080/camel/greetings

{"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 window of the shell prompt where the name service is running.

  6. Now that the name service is unavailable, the circuit breaker kicks in to prevent the greetings service from hanging when it is invoked. Invoke the greetings REST endpoint using the curl command, as follows: 

    $ curl http://localhost:8080/camel/greetings

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

    2019-06-25 09:42:42.766  INFO 11224 --- [-CamelHystrix-6] route2                                   :  Try to call name Service
2019-06-25 09:42:42.771  INFO 11224 --- [-CamelHystrix-6] o.a.c.httpclient.HttpMethodDirector      : I/O exception (java.net.ConnectException) caught when processing request: Connection refused (Connection refused)
2019-06-25 09:42:42.771  INFO 11224 --- [-CamelHystrix-6] o.a.c.httpclient.HttpMethodDirector      : Retrying request
2019-06-25 09:42:42.771  INFO 11224 --- [-CamelHystrix-6] o.a.c.httpclient.HttpMethodDirector      : I/O exception (java.net.ConnectException) caught when processing request: Connection refused (Connection refused)
2019-06-25 09:42:42.771  INFO 11224 --- [-CamelHystrix-6] o.a.c.httpclient.HttpMethodDirector      : Retrying request
2019-06-25 09:42:42.772  INFO 11224 --- [-CamelHystrix-6] o.a.c.httpclient.HttpMethodDirector      : I/O exception (java.net.ConnectException) caught when processing request: Connection refused (Connection refused)
2019-06-25 09:42:42.772  INFO 11224 --- [-CamelHystrix-6] o.a.c.httpclient.HttpMethodDirector      : Retrying request
2019-06-25 09:42:42.781  INFO 11224 --- [-CamelHystrix-6] route2                                   :  We are falling back!!!!
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  7. For more information about this example, visit the Circuit Breaker Mission page at http://localhost:8080/ (while the greetings-service is running). This page provides a link to the Hystrix dashboard, which monitors the state of the circuit breaker.
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