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Scenario: Apache Ambari UI 502 error in Azure HDInsight

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This article describes troubleshooting steps and possible resolutions for issues when interacting with Azure HDInsight clusters.

Issue

When you try to access the Apache Ambari UI for your HDInsight cluster, you get a message similar to: "502 - Web server received an invalid response while acting as a gateway or proxy server."

Cause

In general, the HTTP 502 status code means that Ambari server is not running correctly on the active headnode. There are a few possible root causes.

Resolution

In most of the cases, to mitigate the problem, you can restart the active headnode. Or choose a larger VM size for your headnode.

Ambari server failed to start

You can check ambari-server logs to find out why Ambari server failed to start. One common reason is the database consistency check error. You can find this out in this log file: /var/log/ambari-server/ambari-server-check-database.log.

If you made any modifications to the cluster node, please undo them. Always use Ambari UI to modify any Hadoop/Spark related configurations.

Ambari server taking 100% CPU utilization

In rare situations, we’ve seen ambari-server process has close to 100% CPU utilization constantly. As a mitigation, you can ssh to the active headnode, and kill the Ambari server process and start it again.

ps -ef | grep AmbariServer
top -p <ambari-server-pid>
kill -9 <ambari-server-pid>
service ambari-server start

Ambari server killed by oom-killer

In some scenarios, your headnode runs out of memory, and the Linux oom-killer starts to pick processes to kill. You can verify this situation by searching the AmbariServer process ID, which should not be found. Then look at your /var/log/syslog, and look for something like this:

Jul 27 15:29:30 xxx-xxxxxx kernel: [874192.703153] java invoked oom-killer: gfp_mask=0x23201ca, order=0, oom_score_adj=0

Then identify which processes are taking memories and try to further root cause.

Other issues with Ambari server

Rarely the Ambari server cannot handle the incoming request, you can find more info by looking at the ambari-server logs for any error. One such case is an error like this:

Error Processing URI: /api/v1/clusters/xxxxxx/host_components - (java.lang.OutOfMemoryError) Java heap space

Next steps

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.

  • Connect with @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. Select Support from the menu bar or open the Help + support hub. For more detailed information, review How to create an 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.