Migration guide for CLI commands

[mik-laj]

Hello,

There have been drastic changes to the CLI between Airflow 1.10 and 2.0. However, these changes are not precisely described in UPDATING.md

CLI reorganization
The Airflow CLI has been organized so that related commands are grouped together as subcommands. The airflow list_dags command is now airflow dags list, airflow pause is airflow dags pause, etc. For a complete list of updated CLI commands, see https://airflow.apache.org/cli.html.

https://github.com/apache/airflow/blob/master/UPDATING.md#cli-reorganization.

I would be happy if we had a table to compare new and old commands.

Best regards,
Kamil

[potiuk]

I think we could even implement it in the cli itself - we could add "deprecated" old commands that would print out information about the new commands and exit with error. They could be automatically derived from this documentation created here.

I think changes in the CLI will be a huge surprise to many users so the more information we give the users when they try to run those old commands - the less questions we have and the less issues will be opened in GitHub. We already have some questions from the users trying to use airflow devel "Where is the airflow worker command ? And it's difficult for them to guess that it moved to "celery"

[turbaszek]

I think it's a good idea. We should be able to catch CLI arguments and raise a deprecation warning if someone uses the old command.

[potiuk]

I think it's a good idea. We should be able to catch CLI arguments and raise a deprecation warning if someone uses the old command.

I think even error will be fine in this case -> the CLI is mostly for manual work, so I do not think we should worry about Deprecation here.