I was using HMC 1.0 to install and configure a hadoop test cluster. I wanted to make some changes to /usr/lib/hadoop/conf because the property that I needed to change is not exposed via Manage Services Map Reduce in HMC. I tried to make a manual change to mapred-site.xml and then push the file to all the servers. However, when I restarted Hadoop cluster via HMC, the changes that I made to mapred-site.xml were overridden.
HMC manages node configuration by using Puppet in the background, so any changes done outside of HMC revert back to the HMC known configuration. So the moral of the story is if you want to change any /conf properties on your own, don’t use HMC to cycle mapred.
On the jobtracker node: