Support RABBITMQ_SERVICE_PRIORITY environment variable in rabbitmq-service.bat install

[inikulshin]

Proposed Changes

Support RABBITMQ_SERVICE_PRIORITY environment variable in rabbitmq-service.bat install translating it to
erlsrv.exe's option:

-p[riority] [{low|high|realtime}]
The priority of the Erlang emulator. Default to the Windows default priority.

The reason to avoid manually updating the registry after running the rabbitmq-service.bat install command.

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[lukebakken]

This is the first time anyone has asked to change the service priority. I'm assuming you must have a valid use case for it, what is it? Changing service priority is not something we generally want to encourage with people who use RabbitMQ on Windows. They may think it's a magic cure for other issues they are having.

[inikulshin]

This is the first time anyone has asked to change the service priority. I'm assuming you must have a valid use case for it, what is it?

I admit I don't remember why we (Varonis) started to change the RabbitMQ service priority to high (low and realtime are too dangerous, abovenormal is missing in erlsrv, imo). We just do it (updating registry) in our installation script for years.

But recently I wrote a manual for upgrading Erlang at customer's machine (because of CVE):

1. Open Add or remove programs and find currently installed Erlang (keep opened).
2. Download latest Erlang Windows installer (same major as in 1, 25 or 26).
3. Stop Supervisor and RabbitMQ services.
4. Uninstall Erlang from Add or remove programs
5. Install downloaded Erlang + copy installation directory from wizard. e.g. to clipboard.
6. Set system environment variable ERLANG_HOME to installation directory from 5.
7. Start elevated command prompt and run echo %ERLANG_HOME% && "%RABBITMQ_HOME%\sbin\rabbitmq-service.bat" remove && "%RABBITMQ_HOME%\sbin\rabbitmq-service.bat" install
8. Set Priority in HKEY_LOCAL_MACHINE\SOFTWARE\Ericsson\Erlang\ErlSrv\1.1\RabbitMQ to High (128).
9. Start RabbitMQ and Supervisor services.

And I was wondering if there is a way to get rid of this registry modification step, and found that erlsrv.exe already supports -priority, and I thought: "why not make this minor contribution to rabbitmq-server?" :)

Changing service priority is not something we generally want to encourage with people who use RabbitMQ on Windows. They may think it's a magic cure for other issues they are having.

Since when do you care about the people who use RabbitMQ on Windows? Just joking. :)))

It's still possible (by editing registry) and I don't think the way I implemented it is "encouraging".