GauthamBanasandra opened a new pull request, #5183:
URL: https://github.com/apache/hadoop/pull/5183
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### Description of PR
While launching the AM, the client puts the classpath into environment
HashMap of the ContainerLaunchContext. To support cross-platform compatibility,
some special notations must be used by the client. For example, <CPS> must be
used as the classpath separator instead of ";" (Windows) or ":" (Linux). The NM
would resolve all the <CPS> using the appropriate path separator according to
the OS platform, prior to launching the container. In addition to this, the NM
is also expected to expand and resolve all of the wildcard ( * ) occurrences in
the classpath before launching the container, since the JVM doesn't understand
the wildcard charater.
The issue we see here is, neither <CPS> resolution nor wildcard expansion is
happening.
I tested this from Spark. To run a Spark application on YARN, one needs to
set the spark.yarn.jars config to point to the location where Spark jars are
present. NM would then add these jars to the classpath before launching the
Spark AM container. The resolution didn't happen -
```
Manifest-Version:
1.0
Class-Path:
file:/D:/tmp/hadoop-Gautham/nm-local-dir/usercache/Gautham/appcache/application_1670138957874_0001/container_1670138957874_0001_01_000001/%7B%7BPWD%7D%7D%3CCPS%3E%7B%7BPWD%7D%7D/__spark_conf__%3CCPS%3E%7B%7BPWD%7D%7D/__spark_libs__/*%3CCPS%3E/D:/projects/github/apache/spark/jars/*%3CCPS%3E%7B%7BPWD%7D%7D/__spark_conf__/__hadoop_conf__
file:/D:/tmp/hadoop-Gautham/nm-local-dir/usercache/Gautham/appcache/application_1670138957874_0001/container_1670138957874_0001_01_000001/__spark_conf__/
file:/D:/tmp/hadoop-Gautham/nm-local-dir/usercache/Gautham/appcache/application_1670138957874_0001/container_1670138957874_0001_01_000001/__app__.jar
```
Note that `%3CCPS%3E` in the above code block should've been replaced by ";"
or ":" as part of classpath resolution. Since this didn't happen, NM failed to
launch the Spark AM container -
```
Could not find or load main class
org.apache.spark.deploy.yarn.ApplicationMaster
```
### How was this patch tested?
I tested locally by submitting a Spark job and ensured that it ran
successfully.
### For code changes:
- [x] Does the title or this PR starts with the corresponding JIRA issue id
(e.g. 'HADOOP-17799. Your PR title ...')?
- [ ] Object storage: have the integration tests been executed and the
endpoint declared according to the connector-specific documentation?
- [ ] If adding new dependencies to the code, are these dependencies
licensed in a way that is compatible for inclusion under [ASF
2.0](http://www.apache.org/legal/resolved.html#category-a)?
- [ ] If applicable, have you updated the `LICENSE`, `LICENSE-binary`,
`NOTICE-binary` files?
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