Management commands

Zulip has a number of Django management commands that live under {zerver,zilencer,analytics}/management/commands/.

If you need some Python code to run with a Zulip context (access to the database, etc.) in a script, it should probably go in a management command. The key thing distinguishing these from production scripts (scripts/) and development scripts (tools/) is that management commands can access the database.

While Zulip takes advantage of built-in Django management commands for things like managing Django migrations, we also have dozens that we've written for a range of purposes:

• Cron jobs to do regular updates, e.g., update_analytics_counts.py, sync_ldap_user_data, etc.
• Useful parts of provisioning or upgrading a Zulip development environment or server, e.g., makemessages, compilemessages, populate_db, fill_memcached_caches, etc.
• The actual scripts run by supervisord to run the persistent processes in a Zulip server, e.g., runtornado and process_queue.
• For a sysadmin to verify a Zulip server's configuration during installation, e.g., send_test_email.
• As the interface for doing those rare operations that don't have a UI yet, e.g., deactivate_realm, reactivate_realm, change_user_email (for the case where the user doesn't control the old email address).
• For a sysadmin to easily interact with and script common possible changes they might want to make to the database on a Zulip server. E.g., send_password_reset_email, export, purge_queue.

Writing management commands

It's generally pretty easy to template off an existing management command to write a new one. Some good examples are change_user_email and deactivate_realm. The Django documentation is good, but we have a few pieces advice specific to the Zulip project.

• Inherit from the ZulipBaseCommand class in zerver/lib/management.py; this will add some helpful general flags, as well as tools for adding and parsing --realm and --user flags, so you don't need to write the tedious code of looking those objects up. This is especially important for users, since the library handles the issues around looking up users by email well (if there's a unique user with that email, just modify it without requiring the user to specify the realm as well, but if there's a collision, throw a nice error).
• Avoid writing a lot of code in management commands; management commands are annoying to unit test, and thus easier to maintain if all the interesting logic is in a nice function that is unit tested (and ideally, also used in Zulip's existing code). Look for code in zerver/lib/ that already does what you need. For most actions, you can just call a do_change_foo type function from zerver/actions/ to do all the work; this is usually far better than manipulating the database directly, since the library functions used by the UI are maintained to correctly live-update the UI if needed.

Management commands are essentially independent Python scripts with access to the Zulip server's database and libraries; so you don't need to do anything special like restart the server when iteratively testing one, even if testing in a Zulip production environment where the server doesn't normally restart whenever a file is edited.