Defining a Custom Service

Service Metainfo and Component Category

metainfo.xml

The metainfo.xml file in a Service describes the service, the components of the service and the management scripts to use for executing commands. A component of a service must be either a MASTER, SLAVE or CLIENT category. The <category> tells Ambari what default commands should be available to manage and monitor the component. Details of various sections in metainfo.xml can be found in the Writing metainfo.xml section..

For each Component you must specify the <commandScript> to use when executing commands. There is a defined set of default commands the component must support depending on the components category.

Component Category	Default Lifecycle Commands
MASTER	install, start, stop, configure, status
SLAVE	install, start, stop, configure, status
CLIENT	install, configure, status

Ambari supports different commands scripts written in PYTHON. The type is used to know how to execute the command scripts. You can also create custom commands if there are other commands beyond the default lifecycle commands your component needs to support.

For example, in the YARN Service describes the ResourceManager component as follows in metainfo.xml:

        <component>
          <name>RESOURCEMANAGER</name>
          <category>MASTER</category>
          <commandScript>
            <script>scripts/resourcemanager.py</script>
            <scriptType>PYTHON</scriptType>
            <timeout>600</timeout>
          </commandScript>
          <customCommands>
            <customCommand>
              <name>DECOMMISSION</name>
              <commandScript>
                <script>scripts/resourcemanager.py</script>
                <scriptType>PYTHON</scriptType>
                <timeout>600</timeout>
              </commandScript>
            </customCommand>
          </customCommands>
        </component>

The ResourceManager is a MASTER component, and the command script is scripts/resourcemanager.py, which can be found in the services/YARN/package directory. That command script is PYTHON and that script implements the default lifecycle commands as python methods. This is the install method for the default INSTALL command:

class Resourcemanager(Script):
  def install(self, env):
    self.install_packages(env)
    self.configure(env)

You can also see a custom command is defined DECOMMISSION, which means there is also a decommission method in that python command script:

  def decommission(self, env):
    import params

    ...

    Execute(yarn_refresh_cmd,
            user=yarn_user
    )
    pass

Implementing a Custom Service

In this example, we will create a custom service called "SAMPLESRV". This service includes MASTER, SLAVE and CLIENT components.

Create a Custom Service

Create a directory named SAMPLESRV that will contain the service definition for SAMPLESRV.
```
mkdir SAMPLESRV
cd SAMPLESRV
```

Within the SAMPLESRV directory, create a metainfo.xml file that describes the new service. For example:

<?xml version="1.0"?>
<metainfo>
    <schemaVersion>2.0</schemaVersion>
    <services>
        <service>
            <name>SAMPLESRV</name>
            <displayName>New Sample Service</displayName>
            <comment>A New Sample Service</comment>
            <version>1.0.0</version>
            <components>
                <component>
                    <name>SAMPLESRV_MASTER</name>
                    <displayName>Sample Srv Master</displayName>
                    <category>MASTER</category>
                    <cardinality>1</cardinality>
                    <commandScript>
                        <script>scripts/master.py</script>
                        <scriptType>PYTHON</scriptType>
                        <timeout>600</timeout>
                    </commandScript>
                </component>
                <component>
                    <name>SAMPLESRV_SLAVE</name>
                    <displayName>Sample Srv Slave</displayName>
                    <category>SLAVE</category>
                    <cardinality>1+</cardinality>
                    <commandScript>
                        <script>scripts/slave.py</script>
                        <scriptType>PYTHON</scriptType>
                        <timeout>600</timeout>
                    </commandScript>
                </component>
                <component>
                    <name>SAMPLESRV_CLIENT</name>
                    <displayName>Sample Srv Client</displayName>
                    <category>CLIENT</category>
                    <cardinality>1+</cardinality>
                    <commandScript>
                        <script>scripts/sample_client.py</script>
                        <scriptType>PYTHON</scriptType>
                        <timeout>600</timeout>
                    </commandScript>
                </component>
            </components>
            <osSpecifics>
                <osSpecific>
                    <osFamily>any</osFamily>
                </osSpecific>
            </osSpecifics>
        </service>
    </services>
</metainfo>

In the above, the service name is "SAMPLESRV", and it contains:
- one MASTER component "SAMPLESRV_MASTER"
- one SLAVE component "SAMPLESRV_SLAVE"
- one CLIENT component "SAMPLESRV_CLIENT"
Next, let's create that command script. Create a directory for the command script SAMPLESRV/package/scripts that we designated in the service metainfo.
```
mkdir -p package/scripts
cd package/scripts
```

Within the scripts directory, create the .py command script files mentioned in the metainfo.

For example master.py file:

import sys
from resource_management import *
class Master(Script):
  def install(self, env):
    print 'Install the Sample Srv Master';
  def configure(self, env):
    print 'Configure the Sample Srv Master';
  def stop(self, env):
    print 'Stop the Sample Srv Master';
  def start(self, env):
    print 'Start the Sample Srv Master';
  def status(self, env):
    print 'Status of the Sample Srv Master';
if __name__ == "__main__":
  Master().execute()

For example slave.py file:

import sys
from resource_management import *
class Slave(Script):
  def install(self, env):
    print 'Install the Sample Srv Slave';
  def configure(self, env):
    print 'Configure the Sample Srv Slave';
  def stop(self, env):
    print 'Stop the Sample Srv Slave';
  def start(self, env):
    print 'Start the Sample Srv Slave';
  def status(self, env):
    print 'Status of the Sample Srv Slave';
if __name__ == "__main__":
  Slave().execute()

For example sample_client.py file:

import sys
from resource_management import *
class SampleClient(Script):
  def install(self, env):
    print 'Install the Sample Srv Client';
  def configure(self, env):
    print 'Configure the Sample Srv Client';
if __name__ == "__main__":
  SampleClient().execute()

Implementing a Custom Command

Browse to the SAMPLESRV directory, and edit the metainfo.xml file that describes the service. For example, adding a custom command to the SAMPLESRV_CLIENT:

                <component>
                    <name>SAMPLESRV_CLIENT</name>
                    <displayName>Sample Srv Client</displayName>
                    <category>CLIENT</category>
                    <cardinality>1+</cardinality>
                    <commandScript>
                        <script>scripts/sample_client.py</script>
                        <scriptType>PYTHON</scriptType>
                        <timeout>600</timeout>
                    </commandScript>
                    <customCommands>
                      <customCommand>
                        <name>SOMETHINGCUSTOM</name>
                        <commandScript>
                          <script>scripts/sample_client.py</script>
                          <scriptType>PYTHON</scriptType>
                          <timeout>600</timeout>
                        </commandScript>
                      </customCommand>
                    </customCommands>
                </component>

Next, let's create that command script by editing the package/scripts/sample_client.py file that we designated in the service metainfo.

import sys
from resource_management import *

class SampleClient(Script):
  def install(self, env):
    print 'Install the Sample Srv Client';
  def configure(self, env):
    print 'Configure the Sample Srv Client';
  def somethingcustom(self, env):
    print 'Something custom';

if __name__ == "__main__":
  SampleClient().execute()

Adding Configs to the Custom Service

In this example, we will add a configuration type "test-config" to our SAMPLESRV.

Modify the metainfo.xml

                <component>
                    <name>SAMPLESRV_CLIENT</name>
                    <displayName>Sample Srv Client</displayName>
                    <category>CLIENT</category>
                    <cardinality>1+</cardinality>
                    <commandScript>
                        <script>scripts/sample_client.py</script>
                        <scriptType>PYTHON</scriptType>
                        <timeout>600</timeout>
                    </commandScript>
                    <configFiles>
                      <configFile>
                        <type>xml</type>
                        <fileName>test-config.xml</fileName>
                        <dictionaryName>test-config</dictionaryName>
                      </configFile>
                    </configFiles>
                </component>

Create a directory for the configuration dictionary file SAMPLESRV/configuration.
```
mkdir -p configuration
cd configuration
```

Create the test-config.xml file. For example:

<?xml version="1.0"?>
<?xml-stylesheet type="text/xsl" href="configuration.xsl"?>

<configuration>
  <property>
    <name>some.test.property</name>
    <value>this.is.the.default.value</value>
    <description>This is a test description.</description>
 </property>
</configuration>

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