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 ametainfo.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 themetainfo.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>