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From "Alejandro Fernandez" <afernan...@hortonworks.com>
Subject Re: Review Request 33166: Ambari Agent holding socket open on 50070 prevents NN from starting
Date Tue, 14 Apr 2015 17:41:50 GMT

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This is an automatically generated e-mail. To reply, visit:
https://reviews.apache.org/r/33166/#review80067
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Ship it!


Ship It!

- Alejandro Fernandez


On April 14, 2015, 2:09 p.m., Jonathan Hurley wrote:
> 
> -----------------------------------------------------------
> This is an automatically generated e-mail. To reply, visit:
> https://reviews.apache.org/r/33166/
> -----------------------------------------------------------
> 
> (Updated April 14, 2015, 2:09 p.m.)
> 
> 
> Review request for Ambari, Alejandro Fernandez and Sumit Mohanty.
> 
> 
> Bugs: AMBARI-10464
>     https://issues.apache.org/jira/browse/AMBARI-10464
> 
> 
> Repository: ambari
> 
> 
> Description
> -------
> 
> The Ambari Agent process appears to be listening on port 50070 and holding it open. This
is causing the NN to fail to start until the Ambari Agent is restarted. A netstat -natp reveals
that the agent process has this port open.
> ```
> root@hdp2-02-01 hdfs]# netstat -anp | grep 50070
> tcp 0 0 192.168.1.141:50070 192.168.1.141:50070 ESTABLISHED 1630/python2.6
> ```
> 
> After digging some more through sockets and linux, I think it's entirely possible that
the agent could be assigned a source port that matches the destination port. Anything in the
ephemeral port range is up for grabs. Essentially what is happening here is that NN is down
and when the agent tries to check it via a socket connection to 50070, the source (client)
side of the socket connection binds to 50070 since it's open and within the range specified
by /proc/sys/net/ipv4/ip_local_port_range
> 
> The client essentially connects to itself; the WEB alert connection timeout is set to
10 seconds. That means that after 10 seconds, it will release the connection automatically.
The METRIC alerts, however, use a slightly different mechanism of opening the socket and don't
specify the socket timeout. For a METRIC alert, when both the source and destination ports
are the same, it will connection and hold that connection for as long as socket._GLOBAL_DEFAULT_TIMEOUT
which could be a very long time.
> 
> I believe that we need to change METRIC alert to pass in a timeout value to the socket
(between 5 and 10 seconds just like WEB alerts)
> Since the Hadoop components seem to use emphemeral ports that the OS says are free game
to any client, this will still end up being a problem. The above proposed fix will make it
so that the agent will release the socket after a while preventing the need to restart the
agent after fixing the problem. But it's still possible that the agent could bind to that
port when making its check.
> 
> 
> Diffs
> -----
> 
>   ambari-agent/src/main/python/ambari_agent/alerts/metric_alert.py 8b5f15d 
>   ambari-server/src/main/resources/common-services/HDFS/2.1.0.2.0/package/alerts/alert_checkpoint_time.py
032310d 
>   ambari-server/src/main/resources/common-services/HDFS/2.1.0.2.0/package/alerts/alert_ha_namenode_health.py
058b7b2 
>   ambari-server/src/main/resources/common-services/HIVE/0.12.0.2.0/package/alerts/alert_webhcat_server.py
fb6c4c2 
>   ambari-server/src/main/resources/common-services/YARN/2.1.0.2.0/package/alerts/alert_nodemanager_health.py
8c72f4c 
>   ambari-server/src/main/resources/common-services/YARN/2.1.0.2.0/package/alerts/alert_nodemanagers_summary.py
b297b0c 
>   ambari-server/src/main/resources/stacks/BIGTOP/0.8/services/HDFS/package/files/alert_checkpoint_time.py
032310d 
>   ambari-server/src/main/resources/stacks/BIGTOP/0.8/services/HDFS/package/files/alert_ha_namenode_health.py
058b7b2 
>   ambari-server/src/main/resources/stacks/BIGTOP/0.8/services/WEBHCAT/package/files/alert_webhcat_server.py
fb6c4c2 
>   ambari-server/src/main/resources/stacks/BIGTOP/0.8/services/YARN/package/files/alert_nodemanager_health.py
8c72f4c 
> 
> Diff: https://reviews.apache.org/r/33166/diff/
> 
> 
> Testing
> -------
> 
> I was able to force the alerts to use a specific client port (under Python 2.7) - I chose
50070 since that's the port in this issue. I then verified that when binding, the metric alerts
did not let the port go until the agent was restarted. After the fixes were applied, the agent
was still able to bind to 50070, but it did release it after the specified timeout.
> 
> 
> Thanks,
> 
> Jonathan Hurley
> 
>


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