Is it possible to explicitly specify Erlang version (ERLANG_HOME?) for RabbitMQ .exe installer on Windows?

[inikulshin]

Make Sure ERLANG_HOME is Set didn't work for me.

@lukebakken

The instructions here specify that you are using the .zip file installer (link) and NOT the .exe installer.

However this difference between .zip and .exe installers is pretty unexpected.

It looks like ERLANG_HOME environment variable is ignored and the chosen Erlang version depends only on order of EnumRegKey in
packaging/windows-exe/rabbitmq_nsi.in

Function findErlang

  StrCpy $0 0
  StrCpy $2 "not-found"
  ${Do}
    EnumRegKey $1 HKLM Software\Ericsson\Erlang $0
    ${If} $1 = ""
      ${Break}
    ${EndIf}
    ${If} $1 <> "ErlSrv"
      StrCpy $2 $1
    ${EndIf}

    IntOp $0 $0 + 1
  ${Loop}

And ERLANG_HOME is just overridden in the end:

WriteRegExpandStr ${env_hklm} ERLANG_HOME $0

[lukebakken]

The instructions here specify that you are using the .zip file installer (link) and NOT the .exe installer.

[inikulshin]

@lukebakken you're right, the first line in not related to .exe installer, fixed.

But the rest is. And this difference between .zip and .exe installers is pretty unexpected.
I've updated title question.

[lukebakken]

As you pointed out, the installer will set the ERLANG_HOME environment variable. The workaround is to install RabbitMQ yourself using the zip file and associated rabbitmq-service.bat file to install the Windows service.

[lukebakken]

But why .exe installer can't just keep existing value of ERLANG_HOME? Don't you think it is a bug?

You are the first person to point this out. It's not a bug, just the way the installer has always worked. Using the zip file must be sufficient for most users who wish to keep their existing ERLANG_HOME.

[inikulshin]

I suppose, multiple Erlang installations are very rare. Most of RabbitMQ users don't need more than one, and never had.
We also discovered this behavior by accident mistake, and it doesn't really blocks us.

And it is not a bug:

https://www.rabbitmq.com/install-windows.html#installer

• There must be only one Erlang version installed at a time

Thank you.

[inikulshin]

Actually, .exe installer iterates only on 64-bit Erlangs, so the prerequisite is

There must be only one 64-bit Erlang version installed at a time

[michaelklishin]

No one should ever run 32-bit Erlang for RabbitMQ (or anything else). 64-bit is the implicit assumption and it has been for years. The limited memory address space makes 32-bit a no-go for data services.

[inikulshin]

@michaelklishin sure.

I just wanted to mention, that any number of installed 32-bit Erlangs (in addition to the only one prerequisite 64-bit) does not affect .exe installer.

Erlang is a different product, people may install and use it regardless RabbitMQ...

[lukebakken]

If you'd like to open a pull request to make the installer detect the presence of ERLANG_HOME I think that would be reasonable (cc @michaelklishin).