Siddharth Ahuja created YARN-9585:
-------------------------------------
Summary: Order of environment variables set up inside
ContainerLaunchContext cannot be guaranteed inside the launch_container.sh
resulting in inconsistent resolution of transitive environment variables
Key: YARN-9585
URL: https://issues.apache.org/jira/browse/YARN-9585
Project: Hadoop YARN
Issue Type: Improvement
Components: nodemanager
Reporter: Siddharth Ahuja
Transitive dependencies amongst environment variables set up inside the
ContainerLaunchContext cannot be guaranteed to be resolved consistently during
the setup of the container launch script.
For example, when environment variables are set in the following order inside
the ContainerLaunchContext:
{code}
A_HOME=/path/to/A
PATH=$A_HOME:/path/to/somethingelse
{code}
the "export" inside the launch_container.sh may not happen in the same order
which would mean that the launch_container.sh may look like this:
{code}
#!/bin/bash
…
echo "Setting up env variables"
…
export PATH=$A_HOME:/path/to/somethingelse
export A_HOME=/path/to/A
whereas the expectation would be:
export A_HOME=/path/to/A
export PATH=/path/to/A:/path/to/somethingelse
{code}
The explanation of this behaviour is as per below:
>From [1] and [2], we can see that the environment variables are getting
>exported inside the launch container script by the Java code. The key thing to
>note here is that the environment variables are retrieved from inside a "Map".
> From [3], [4] and [5], this map is a HashMap and from [6], the order of
>entries (env vars in this case) cannot be guaranteed.
Therefore, the "export" order of the environment variables inside the
launch_container.sh script cannot be guaranteed as a result.
As such, this explains the inconsistent nature of the working of transitive
dependencies.
It does not seem that transitive dependencies can be handled correctly based on
the current code implementation, as such, I have gone ahead and raised this
JIRA after discussion with [~wilfreds] to look into this improvement in the
future.
[1]
https://github.com/apache/hadoop/blob/release-3.0.0-RC0/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-nodemanager/src/main/java/org/apache/hadoop/yarn/server/nodemanager/ContainerExecutor.java#L353
[2]
https://github.com/apache/hadoop/blob/release-3.0.0-RC0/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-nodemanager/src/main/java/org/apache/hadoop/yarn/server/nodemanager/containermanager/launcher/ContainerLaunch.java#L1200
[3]
https://github.com/apache/hadoop/blob/release-3.0.0-RC0/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-nodemanager/src/main/java/org/apache/hadoop/yarn/server/nodemanager/containermanager/launcher/ContainerLaunch.java#L203
[4]
https://github.com/apache/hadoop/blob/release-3.0.0-RC0/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-common/src/main/java/org/apache/hadoop/yarn/api/records/impl/pb/ContainerLaunchContextPBImpl.java#L383
[5]
https://github.com/apache/hadoop/blob/release-3.0.0-RC0/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-common/src/main/java/org/apache/hadoop/yarn/api/records/impl/pb/ContainerLaunchContextPBImpl.java#L393
[6] https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html
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