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Each custom service can define its upgrade within its service definition.  This allows the custom service to be integrated within the stack's upgrade.

Service Upgrade Packs

Each service can define upgrade-packs, which are XML files describing the upgrade process of that particular service and how the upgrade pack relates to the overall stack upgrade-packs. These upgrade-pack XML files are placed in the service's upgrades/ folder in separate sub-folders specific to the stack-version they are meant to extend.  Some examples of this can be seen in the testing code.

Examples

Matching Upgrade Packs

Each upgrade-pack that the service defines should match the file name of the service defined by a particular stack version.  For example in the testing code, HDP 2.2.0 had an upgrade_test_15388.xml upgrade-pack.  The HDFS service defined an extension to that upgrade pack HDP/2.0.5/services/HDFS/upgrades/HDP/2.2.0/upgrade_test_15388.xml.  In this case the upgrade-pack was defined in the HDP/2.0.5 stack.  The upgrade-pack is an extension to HDP/2.2.0 because it is defined in upgrade/HDP/2.2.0 directory.  Finally the name of the service's extension to the upgrade-pack upgrade_test_15388.xml matches the name of the upgrade-pack in HDP/2.2.0/upgrades.

Upgrade XML Format

The file format for the service is much the same as that of the stack.  The target, target-stack and type attributes should all be the same as the stack's upgrade-pack. 

Prerequisite Checks

The service is able to add its own prerequisite checks.

General Attributes and Prerequisite Checks
<upgrade xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <target>2.4.*</target>
  <target-stack>HDP-2.4.0</target-stack>
  <type>ROLLING</type>
  <prerequisite-checks>
    <check>org.apache.ambari.server.checks.FooCheck</check>
  </prerequisite-checks>

Order Section

The order section of the upgrade-pack, consists of group elements just like the stack's upgrade-pack.  The key difference is defining how these groups relate to groups in the stack's upgrade pack or other service upgrade-packs.  In the first example we are referencing the PRE_CLUSTER group and adding a new execute-stage for the service FOO.  The entry is supposed to be added after the execute-stage for HDFS based on the <add-after-group-entry> tag.

Order Section - Add After Group Entry
  <order>
    <group xsi:type="cluster" name="PRE_CLUSTER" title="Pre {{direction.text.proper}}">
      <add-after-group-entry>HDFS</add-after-group-entry>
      <execute-stage service="FOO" component="BAR" title="Backup FOO">
        <task xsi:type="manual">
          <message>Back FOO up.</message>
        </task>
      </execute-stage>
    </group>

The same syntax can be used to order other sections like service check priorities and group services.

Order Section - Further Add After Group Entry Examples
    <group name="SERVICE_CHECK1" title="All Service Checks" xsi:type="service-check">
      <add-after-group-entry>ZOOKEEPER</add-after-group-entry>
      <priority>
        <service>HBASE</service>
      </priority>
    </group>

    <group name="CORE_MASTER" title="Core Masters">
      <add-after-group-entry>YARN</add-after-group-entry>
      <service name="HBASE">
        <component>HBASE_MASTER</component>
      </service>
    </group>

It is also possible to add new groups and order them after other groups in the stack's upgrade-packs.  In the following example, we are adding the FOO group after the HIVE group using the add-after-group tag.

Order Section - Add After Group
    <group name="FOO" title="Foo">
      <add-after-group>HIVE</add-after-group>
      <skippable>true</skippable>
      <allow-retry>false</allow-retry>
      <service name="FOO">
        <component>BAR</component>
      </service>
    </group>

You could also include both the add-after-group and the add-after-group-entry tags in the same group.  This will create a new group if it doesn't already exist and will order it after the add-after-group's group name.  The add-after-group-entry will determine the internal ordering of that group's services, priorities or execute stages.

Order Section - Add After Group
    <group name="FOO" title="Foo">
      <add-after-group>HIVE</add-after-group>
      <add-after-group-entry>FOO</add-after-group-entry>
      <skippable>true</skippable>
      <allow-retry>false</allow-retry>
      <service name="FOO2">
        <component>BAR2</component>
      </service>
    </group>

Processing Section

The processing section of the upgrade-pack remains the same as what it would be in the stack's upgrade-pack.

Processing Section
   <processing>
    <service name="FOO">
      <component name="BAR">
        <upgrade>
          <task xsi:type="restart-task" />
        </upgrade>
      </component>
      <component name="BAR2">
        <upgrade>
          <task xsi:type="restart-task" />
        </upgrade>
      </component>
    </service>
  </processing>
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