Enable celery command in any environment

[zeroam]

Set celery command visible even if the executor is not CeleryExecutor
Instead, raise ArgumentError and display help message when the executor is
not CeleryExecutor

airflow command
Before:

After:

airflow celery command
After (executor is SequentialExecutor):

reference from: #7873, #7070
reviewed from: @mik-laj, @turbaszek

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Issue link: WILL BE INSERTED BY boring-cyborg

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• Description above provides context of the change
• Unit tests coverage for changes (not needed for documentation changes)
• Commits follow "How to write a good git commit message"
• Relevant documentation is updated including usage instructions.
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[turbaszek]

What would you say to write a nice message in case of airflow celery + LocalExecutor instead of raising an exception? I would feel better with "Hey this work only with celery, so no action was taken" than with stacktrace from exception :)

[zeroam]

What would you say to write a nice message in case of airflow celery + LocalExecutor instead of raising an exception? I would feel better with "Hey this work only with celery, so no action was taken" than with stacktrace from exception :)

@turbaszek Thanks! How about this one?

This shows help message instead of Exception.

[turbaszek]

What would you say to write a nice message in case of airflow celery + LocalExecutor instead of raising an exception? I would feel better with "Hey this work only with celery, so no action was taken" than with stacktrace from exception :)

@turbaszek Thanks! How about this one?

This shows help message instead of Exception.

Definitely better! What about "celery command works only with CeleryExecutor, your current executor: ExecutorName. For more information check the help above"

Also, would you mind to extend current desription of celery sub command? For example:
"Start celery components. Works only when using CeleryExecutor for more information see: here_link_to_docs"

[zeroam]

@turbaszek your suggestion is more clear! I've changed help message and changed celery subcommand help message

[zhongjiajie]

Some minor suggest.

[zhongjiajie]

Suggested change

	'Start celery components. Works only when using CeleryExecutor. for more information, see '
	'Start celery components. Works only when using CeleryExecutor. For more information, see '

[zhongjiajie]

BTW, code LGTM

[turbaszek]

Hi @zeroam Travis is sad due to some static checks. Please take a look at our pre-commits:
https://github.com/apache/airflow/blob/master/STATIC_CODE_CHECKS.rst

[zeroam]

@turbaszek Thanks for the advice!
I checked pre-commit and passed the static test.
but I failed in test_celery_command

FAILED tests/cli/commands/test_celery_command.py::TestCeleryStopCommand::test_if_right_pid_is_read - SystemExit: 2
FAILED tests/cli/commands/test_celery_command.py::TestCeleryStopCommand::test_same_pid_file_is_used_in_start_and_stop - SystemExit: 2
FAILED tests/cli/commands/test_celery_command.py::TestWorkerStart::test_worker_started_with_required_arguments - SystemExit: 2

I will fix it up

[codecov-io]

Codecov Report

Merging #7902 into master will decrease coverage by 0.63%.
The diff coverage is 63.63%.

@@            Coverage Diff             @@
##           master    #7902      +/-   ##
==========================================
- Coverage   87.16%   86.52%   -0.64%     
==========================================
  Files         931      932       +1     
  Lines       45155    45191      +36     
==========================================
- Hits        39358    39101     -257     
- Misses       5797     6090     +293     

Impacted Files	Coverage Δ
airflow/cli/cli_parser.py	97.24% <63.63%> (-0.89%)	⬇️
...flow/providers/apache/cassandra/hooks/cassandra.py	21.25% <0.00%> (-72.50%)	⬇️
airflow/kubernetes/volume_mount.py	44.44% <0.00%> (-55.56%)	⬇️
airflow/providers/postgres/operators/postgres.py	47.82% <0.00%> (-52.18%)	⬇️
airflow/providers/redis/operators/redis_publish.py	50.00% <0.00%> (-50.00%)	⬇️
airflow/kubernetes/volume.py	52.94% <0.00%> (-47.06%)	⬇️
airflow/providers/mongo/sensors/mongo.py	53.33% <0.00%> (-46.67%)	⬇️
airflow/kubernetes/pod_launcher.py	47.18% <0.00%> (-45.08%)	⬇️
airflow/providers/redis/sensors/redis_key.py	61.53% <0.00%> (-38.47%)	⬇️
airflow/executors/celery_executor.py	50.67% <0.00%> (-37.84%)	⬇️
... and 10 more

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[potiuk]

Great change. I think it's better to show all commands and do not make it depend on the current configuration. It's much better for discovery.