ts_ambari9

Author: dagiro

articles/hdinsight/TOC.yml

@@ -38,7 +38,9 @@
     - name: Apache Hadoop components on HDInsight
       href: ./hdinsight-component-versioning.md
     - name: High availability components
-      href: ./hdinsight-high-availability-components.md     
+      href: ./hdinsight-high-availability-components.md   
+    - name: Apache Ambari in Azure HDInsight
+      href: ./apache-ambari-usage.md  
     - name: Machine learning in HDInsight
       href: ./hdinsight-machine-learning-overview.md
     - name: Streaming at scale in HDInsight

articles/hdinsight/apache-ambari-usage.md

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+---
+title: Apache Ambari usage in Azure HDInsight
+description: Discussion of how Apache Ambari is used in Azure HDInsight.
+author: hrasheed-msft
+ms.author: hrasheed
+ms.reviewer: jasonh
+ms.service: hdinsight
+ms.topic: conceptual
+ms.date: 02/05/2020
+---
+
+# Apache Ambari usage in Azure HDInsight
+
+HDInsight uses Apache Ambari for cluster deployment and management. Ambari agents run on every node (headnode, worker node, zookeeper, and edgenode if exists). Ambari server runs only on headnode (hn0 or hn1). Only one instance of Ambari server shall run at one time. This is controlled by HDInsight failover controller. When one of the headnodes is down for reboot or maintenance, the other headnode will become active and Ambari server on the second headnode will be started.
+
+All cluster configuration should be done through the [Ambari UI](./hdinsight-hadoop-manage-ambari.md), any local change will be overwritten when the node is restarted.
+
+## Failover controller services
+
+The HDInsight failover controller is also responsible for updating the IP address of headnode host, which points to the current active head node. All Ambari agents are configured to report its state and heartbeat to headnode host. The failover controller is a set of services running on every node in the cluster, if they aren't running, the headnode failover may not work correctly and you'll end up with HTTP 502 when trying to access Ambari server.
+
+To check which headnode is active, one way is to ssh to one of the nodes in the cluster, then run `ping headnodehost` and compare the IP with that of the two headnodes.
+
+If failover controller services aren't running, headnode failover may not happen correctly, which may end up not running Ambari server. To check if failover controller services are running, execute:
+
+```bash
+ps -ef | grep failover
+```
+
+## Logs
+
+On the active headnode, you can check the Ambari server logs at:
+
+```
+/var/log/ambari-server/ambari-server.log
+/var/log/ambari-server/ambari-server-check-database.log
+```
+
+On any node in the cluster, you can check the Ambari agent logs at:
+
+```bash
+/var/log/ambari-agent/ambari-agent.log
+```
+
+## Service start sequences
+
+This is the sequence of service start at boot time:
+
+1. Hdinsight-agent starts failover controller services.
+1. Failover controller services start Ambari agent on every node and Ambari server on active headnode.
+
+## Ambari Database
+
+HDInsight creates SQL Azure Database under the hood to serve as the database for Ambari server. The default [service tier is S0](../sql-database/sql-database-elastic-pool-scale.md).
+
+For any cluster with worker node count bigger than 16 when creating the cluster, S2 is the database service tier.
+
+## Takeaway points
+
+Never manually start/stop ambari-server or ambari-agent services, unless you're trying to restart the service to work around an issue. To force a failover, you can reboot the active headnode.
+
+Never manually modify any configuration files on any cluster node, let Ambari UI do the job for you.
+
+## Next steps
+
+* [Manage HDInsight clusters by using the Apache Ambari Web UI](hdinsight-hadoop-manage-ambari.md)
+* [Manage HDInsight clusters by using the Apache Ambari REST API](hdinsight-hadoop-manage-ambari-rest-api.md)
+
+If you didn't see your problem or are unable to solve your issue, visit one of the following channels for more support:
+
+* Get answers from Azure experts through [Azure Community Support](https://azure.microsoft.com/support/community/).
+
+* Connect with [@AzureSupport](https://twitter.com/azuresupport) - the official Microsoft Azure account for improving customer experience. Connecting the Azure community to the right resources: answers, support, and experts.
+
+* If you need more help, you can submit a support request from the [Azure portal](https://portal.azure.com/?#blade/Microsoft_Azure_Support/HelpAndSupportBlade/). Select **Support** from the menu bar or open the **Help + support** hub. For more detailed information, review [How to create an Azure support request](https://docs.microsoft.com/azure/azure-supportability/how-to-create-azure-support-request). Access to Subscription Management and billing support is included with your Microsoft Azure subscription, and Technical Support is provided through one of the [Azure Support Plans](https://azure.microsoft.com/support/plans/).