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| <property><name>zookeeper.znode.parent</name><value>/hbase-unsecure</value></property> |
zookeeper.znode.parent is a config property associated with hbase-site in HBase.
While adding config properties there are a few scenarios to keep in mind. Go through them to see what is applicable for the specific set of config changes you are doing.
Where should the property be added?
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E.g https://github.com/apache/ambari/blob/branch-2.4/ambari-server/src/main/resources/common-services/KAFKA/0.9.0/configuration/kafka-broker.xml#L27-L32 added to KAFKA/0.9.0 and not KAFKA/0.8.1. KAFKA in HDP-2.3 derives from KAFKA/0.9.0 https://github.com/apache/ambari/blob/branch-2.4/ambari-server/src/main/resources/stacks/HDP/2.3/services/KAFKA/metainfo.xml#L24
If the property is not valid no longer supported starting a higher config Service version then ensure that the property is deleted in the higher starting that specific Service version. E.g. https://github.com/apache/ambari/blob/branch-2.4/ambari-server/src/main/resources/common-services/ATLAS/0.7.0.2.5/configuration/application-properties.xml#L226-L230
Note: It is not typical standard to just remove delete config properties from a released stack definition. If you absolutely must then ensure that there is corresponding Ambari upgrade code to remove the config property as well.
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- The default value may be fine (very typical)
- The default value may be modified for specific deployments using stack advisor (e.g. default is not optimal) - E.g. https://github.com/apache/ambari/blob/branch-2.4/ambari-server/src/main/resources/stacks/HDP/2.5/services/stack_advisor.py#L80 oozie_admin_users must should include the falcon service user if falcon exists.
- The default value must be modified (typically properties with localhost or host list) - E.g. https://github.com/apache/ambari/blob/branch-2.4/ambari-server/src/main/resources/stacks/HDP/2.5/services/stack_advisor.py#L496 ATLAS rest address, atlas.rest.address, must be constructed based on where the ATLAS server is installed.
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The typical behavior is that Ambari upgrade must not modify stack configurations. It is critical for deployed stack to not take an outage (e.g. restart services) after performing an Ambari upgrade. It is ensured by specifying <on-ambari-upgrade add="false"/> to the config property. Due to historical reasons this is not the default behavior. Earlier versions of Ambari added any missing properties on upgrade. So several existing python scripts assume the existence of the properties.
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- Specify <on-ambari-upgrade add="true"/> and if the property does not exist in the configurations, it will be added with the default value specified
- Explicitly add config property through upgrade catalog. This is needed if appropriate value must be calculated based on the cluster details. E.g. https://github.com/apache/ambari/blob/branch-2.4/ambari-server/src/main/java/org/apache/ambari/server/upgrade/UpgradeCatalog240.java#L2928 set HBase, hbase.coprocessor.master.classes, to appropriate values based on if Kerberos/Ranger is enabled.
Note: As Ambari upgrade does not add new config properties by default ensure that you have appropriate defaults while reading the configs. E.g. https://github.com/apache/ambari/blob/trunk/ambari-server/src/main/resources/common-services/HBASE/0.96.0.2.0/package/scripts/params_linux.py#L81
What should happen on Stack upgrade
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Display characteristics of the config property
See - Enhanced Configs
Misc best-practices
- Prefer setting config property values using stack-advisor (its common across all deployment mechanism, UI, blueprint)
- Avoid inclusion of new config properties or modification of config properties in the configure() implantation of the component. This is not visible to the user and thus results in configs on disk not being the same as the config accessible via API/UI
- Do add description for all config properties
- Add dependencies to other config properties as needed. Dependencies are required to ensure that stack advisor is called when dependencies change in value or are deleted (e.g. service delete)