[FLINK-14306] flink-python build fails with No module named pkg_resources

• Type: Bug
• Status: Closed
• Priority: Critical
• Resolution: Fixed
• Affects Version/s: 1.10.0
• Fix Version/s: 1.10.0
• Component/s: API / Python, Build System
• Labels: pull-request-available
• Assignee: Dian Fu
• Reporter: Piotr Nowojski
• Created: 01/Oct/19 11:27
• Updated: 10/Oct/19 11:40
• Resolved: 09/Oct/19 15:29

Description

Benchmark builds started to fail with

[INFO] Adding generated sources (java): /home/jenkins/workspace/flink-master-benchmarks/flink/flink-python/target/generated-sources
[INFO] 
[INFO] --- exec-maven-plugin:1.5.0:exec (Protos Generation) @ flink-python_2.11 ---
Traceback (most recent call last):
  File "/home/jenkins/workspace/flink-master-benchmarks/flink/flink-python/pyflink/gen_protos.py", line 33, in <module>
    import pkg_resources
ImportError: No module named pkg_resources
[ERROR] Command execution failed.
(...)
[INFO] flink-state-processor-api .......................... SUCCESS [  0.299 s]
[INFO] flink-python ....................................... FAILURE [  0.434 s]
[INFO] flink-scala-shell .................................. SKIPPED

because of this ticket: https://issues.apache.org/jira/browse/FLINK-14018

I think I can solve the benchmark builds failing quite easily by installing setuptools python package, so this ticket is not about this, but about deciding how should we treat such kind of external dependencies. I don't see this dependency being mentioned anywhere in the documentation (for example here).

Probably at the very least those external dependencies should be documented, but also I fear about such kind of manual steps to do before building the Flink can become a problem if grow out of control. Some questions:

1. Do we really need this dependency?
2. Could this dependency be resolve automatically? By installing into a local python virtual environment?
3. Should we document those dependencies somewhere?
4. Maybe we should not build flink-python by default?
5. Maybe we should add a pre-build script for flink-python to verify the dependencies and to throw an easy to understand error with hint how to fix it?

CC hequn dian.fu trohrmann jincheng

Issue Links

• is caused by: FLINK-14018 Add Python building blocks to make sure the basic functionality of Python ScalarFunction could work
• links to: GitHub Pull Request #9855