Cloudera Manager Agents
The Cloudera Manager Agent is a Cloudera Manager component that works with the Cloudera Manager Server to manage the processes that map to role instances.
In a Cloudera Manager managed cluster, you can only start or stop role instance processes using Cloudera Manager. Cloudera Manager uses an open source process management tool called supervisord, that starts processes, takes care of redirecting log files, notifying of process failure, setting the effective user ID of the calling process to the right user, and so on. Cloudera Manager supports automatically restarting a crashed process. It will also flag a role instance with a bad health flag if its process crashes repeatedly right after start up.
The Agent is started by
start-up. It, in turn, contacts the Cloudera Manager Server and determines
which processes should be running. The Agent is monitored as part of
Cloudera Manager's host monitoring. If the Agent stops heartbeating, the
host is marked as having bad health.
One of the Agent's main responsibilities is to start
and stop processes. When the Agent detects a new process from the Server
heartbeat, the Agent creates a directory for it in
/var/run/cloudera-scm-agent and unpacks the
configuration. It then contacts
supervisord, which starts
To enable Cloudera Manager to run scripts in subdirectories of
/var/run is mounted
noexec in many
Linux distributions), Cloudera Manager mounts a
(temporary file storage), named
tmpfs defaults to a max size of 50% of physical RAM
but this space is not allocated until its used, and tmpfs is paged out
to swap if there is memory pressure.
The lifecycle actions of
cmprocesses can be described
by the following statements:
- Created when the Agent starts up for the first time with a new supervisord process.
- If it already exists without
noexec, reused when the Agent is started using
startand not recreated.
- Remounted if Agent is started using
- Unmounting and remounting cleans out the contents (since it is mounted as a tmpfs).
- Unmounted when the host is rebooted.
- Not unmounted when the Agent is stopped.