Gera Shegalov created YARN-1996:
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Summary: Provide alternative policies for UNHEALTHY nodes.
Key: YARN-1996
URL: https://issues.apache.org/jira/browse/YARN-1996
Project: Hadoop YARN
Issue Type: New Feature
Components: nodemanager, scheduler
Affects Versions: 2.4.0
Reporter: Gera Shegalov
Assignee: Gera Shegalov
Currently, UNHEALTHY nodes can significantly prolong execution of large
expensive jobs as demonstrated by MAPREDUCE-5817, and downgrade the cluster
health even further due to [positive
feedback|http://en.wikipedia.org/wiki/Positive_feedback]. A container set that
might have deemed the node unhealthy in the first place starts spreading across
the cluster because the current node is declared unusable and all its
containers are killed and rescheduled on different nodes.
To mitigate this, we experiment with a patch that allows containers already
running on a node turning UNHEALTHY to complete (drain) whereas no new
container can be assigned to it until it turns healthy again.
This mechanism can also be used for graceful decommissioning of NM. To this
end, we have to write a health script such that it can deterministically
report UNHEALTHY. For example with
{code}
if [ -e $1 ] ; then
echo ERROR Node decommmissioning via health script hack
fi
{code}
In the current version patch, the behavior is controlled by a boolean property
{{yarn.nodemanager.unheathy.drain.containers}}. More versatile policies are
possible in the future work. Currently, the health state of a node is binary
determined based on the disk checker and the health script ERROR outputs.
However, we can as well interpret health script output similar to java logging
levels (one of which is ERROR) such as WARN, FATAL. Each level can then be
treated differently. E.g.,
- FATAL: unusable like today
- ERROR: drain
- WARN: halve the node capacity.
complimented with some equivalence rules such as 3 WARN messages == ERROR,
2*ERROR == FATAL, etc.
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