This alert is triggered when the configured critical threshold of TaskTracker hosts
become inaccessible in a short time-window. It uses the check_aggregate plugin to aggregate
the results of individual Tasktracker process down alert checks.
Connectivity issues such as general network problems, switch failures on the top-of-the-rack, etc.
Check the JobTracker UI for the list of TaskTrackers. If you see a lot of down TaskTrackers on a small set of racks, check for network connectivity issues between the racks
Check for errors in the TaskTracker logs on the individual machines (see TaskTracker Process Down Alert section for more information)
Fix the hardware/network issues and restart the TaskTrackers
