Run Docker on YARN using the YARN services API

Create the following Yarnfile and save it to /tmp/httpd.json:


 {  
   "name":"httpd-service",
   "version":"1.0.0",
   "lifetime":"3600",
   "configuration":{  
      "properties":{  
         "docker.network":"bridge"
      }
   },
   "components":[  
      {  
         "name":"httpd",
         "number_of_containers":2,
         "artifact":{  
            "id":"centos/httpd-24-centos7:latest",
            "type":"DOCKER"
         },
         "launch_command":"/usr/bin/run-httpd",
         "resource":{  
            "cpus":1,
            "memory":"1024"
         },
         "readiness_check":{  
            "type":"HTTP",
            "properties":{  
               "url":"http://${THIS_HOST}:8080"
            }
         },
         "configuration":{  
            "files":[  
               {  
                  "type":"TEMPLATE",
                  "dest_file":"/var/www/html/index.html",
                  "properties":{  
                     "content":"<html><header><title>Title</title></header><body>Hello from ${COMPONENT_INSTANCE_NAME}!</body></html>"
                  }
               }
            ]
         }
      },
      {  
         "name":"httpd-proxy",
         "number_of_containers":1,
         "dependencies":[  
            "httpd"
         ],
         "artifact":{  
            "id":"centos/httpd-24-centos7:latest",
            "type":"DOCKER"
         },
         "launch_command":"/usr/bin/run-httpd",
         "resource":{  
            "cpus":1,
            "memory":"1024"
         },
         "configuration":{  
            "files":[  
               {  
                  "type":"TEMPLATE",
                  "dest_file":"/etc/httpd/conf.d/httpd-proxy.conf",
                  "src_file":"httpd-proxy-no-dns.conf"
               }
            ]
         }
      }
   ]
}

Copy the HTTPD proxy configuration to HDFS. This configuration will be used to configure the HTTPD proxy container to load balance traffic between two backend HTTPD servers.

hdfs dfs -copyFromLocal /usr/hdp/current/hadoop-yarn-client/yarn-service-examples/httpd-no-dns/httpd-proxy-no-dns.conf

Submit the HTTPD application using the YARN CLI:

yarn app -launch httpdservice /tmp/httpd.json

Once the application has launched, get the IP address for the HTTPD proxy container to validate that the backend servers have successfully started. The components need to reach a STABLE state and the containers a READY state in the status output before proceeding with next step.

yarn app -status httpdservice

	Note
	use `jq` or `python -m json.tool` to pretty print the output.

The output will appear as follows.


{  
   "name":"httpdservice",
   "id":"application_1525954234278_0006",
   "lifetime":3549,
   "components":[  
      {  
         "name":"httpd",
         "dependencies":[  

         ],
         "artifact":{  
            "id":"centos/httpd-24-centos7:latest",
            "type":"DOCKER"
         },
         "resource":{  
            "cpus":1,
            "memory":"1024",
            "additional":{  

            }
         },
         "state":"STABLE",
         "configuration":{  
            "properties":{  
               "docker.network":"bridge"
            },
            "env":{  

            },
            "files":[  
               {  
                  "type":"TEMPLATE",
                  "properties":{  
                     "content":"<html><header><title>Title</title></header><body>Hello from ${COMPONENT_INSTANCE_NAME}!</body></html>"
                  },
                  "dest_file":"/var/www/html/index.html"
               }
            ]
         },
         "quicklinks":[  

         ],
         "containers":[  
            {  
               "id":"container_1525954234278_0006_01_000002",
               "ip":"172.17.0.2",
               "hostname":"httpd-0.httpdservice.user.domain",
               "state":"READY",
               "launch_time":1525980550770,
               "bare_host":"node.domain",
               "component_instance_name":"httpd-0"
            },
            {  
               "id":"container_1525954234278_0006_01_000003",
               "ip":"172.17.0.3",
               "hostname":"httpd-1.httpdservice.user.domain",
               "state":"READY",
               "launch_time":1525980551772,
               "bare_host":"node.domain",
               "component_instance_name":"httpd-1"
            }
         ],
         "readiness_check":{  
            "type":"HTTP",
            "properties":{  
               "url":"http://${THIS_HOST}:8080"
            }
         },
         "launch_command":"/usr/bin/run-httpd",
         "number_of_containers":2,
         "run_privileged_container":false
      },
      {  
         "name":"httpd-proxy",
         "dependencies":[  
            "httpd"
         ],
         "artifact":{  
            "id":"centos/httpd-24-centos7:latest",
            "type":"DOCKER"
         },
         "resource":{  
            "cpus":1,
            "memory":"1024",
            "additional":{  

            }
         },
         "state":"STABLE",
         "configuration":{  
            "properties":{  
               "docker.network":"bridge"
            },
            "env":{  

            },
            "files":[  
               {  
                  "type":"TEMPLATE",
                  "properties":{  

                  },
                  "dest_file":"/etc/httpd/conf.d/httpd-proxy.conf",
                  "src_file":"httpd-proxy-no-dns.conf"
               }
            ]
         },
         "quicklinks":[  

         ],
         "containers":[  
            {  
               "id":"container_1525954234278_0006_01_000005",
               "ip":"172.17.0.4",
               "hostname":"httpd-proxy-0.httpdservice.user.domain",
               "state":"READY",
               "launch_time":1525980579818,
               "bare_host":"node.domain",
               "component_instance_name":"httpd-proxy-0"
            }
         ],
         "launch_command":"/usr/bin/run-httpd",
         "number_of_containers":1,
         "run_privileged_container":false
      }
   ],
   "configuration":{  
      "properties":{  
         "docker.network":"bridge"
      },
      "env":{  

      },
      "files":[  

      ]
   },
   "state":"STARTED",
   "quicklinks":{  

   },
   "version":"1.0.0",
   "kerberos_principal":{  

   }
}

Find the details regarding the httpd-proxy-0 instance and record the IP address associated with the container. In the example above, the IP is 172.17.0.4.

Using curl, or a similar HTTP client, perform a GET request to the HTTPD proxy on port 8080, using the IP address obtained in the previous step.

curl http://172.17.0.4:8080/

The requests should be routed to both backend HTTPD servers, as seen in the following output:

[user@node ~]$ curl http://172.17.0.4:8080/ <html><header><title>Title</title></header><body>Hello from httpd-0!</body></html>

[user@node ~]$ curl http://172.17.0.4:8080/ <html><header><title>Title</title></header><body>Hello from httpd-1!</body></html>

[user@node ~]$ curl http://172.17.0.4:8080/ <html><header><title>Title</title></header><body>Hello from httpd-0!</body></html>

[user@node ~]$ curl http://172.17.0.4:8080/ <html><header><title>Title</title></header><body>Hello from httpd-1!</body></html>