Order of environment variables set up inside ContainerLaunchContext cannot be guaranteed inside the launch_container.sh resulting in inconsistent resolution of transitive environment variables

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:

A_HOME=/path/to/A
PATH=$A_HOME:/path/to/somethingelse

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:

#!/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

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 based on the current code implementation.

I have raised this JIRA after discussion with wilfreds to look into the improvement of this behaviour 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