Deploying program on erlang runtime 21

[Dave Cottlehuber]

On Wed, 29 May 2019, at 20:31, Joe Love wrote:
> Hi,
> 
> I’ve been trying to wrap my head around creating my Elixir-based 
> projects on my client workstations (which are not freebsd) and 
> deploying them to a FreeBSD server using the erlang-runtime-21 package.
> 
> I think I’m a bit lost somewhere on it, and am hoping to get some guidance here.
> 
> I’ve created my project on my mac.  I’ve added Distillery (per many 
> suggestions & guides).  If I understand everything correctly, I can’t 
> include ERTS, as that’s the part which is compiled based on the host 
> OS.  Therefore, I modified my Distillery config to not include ERTS in 
> the production build, and then ran `mix release --env=prod`.
> 
> I uploaded the resulting _build/dev/rel/myproject to the FreeBSD server 
> which has erlang-runtime-21 on it.
> I set my path to include /usr/local/lib/erlang21/bin, added 
> ERTS_LIB_DIR = /usr/local/lib/erlang21/erts-10.3 and tried to run it.  
> Apparently I have erts-10.1 on my machine and the server had erts-10.3, 
> so it seems that that also needs to match.
> 
> So, given all of this, I remember being told that while the lang/erlang 
> port was older, that I could always use the runtime ports, and things 
> would work.  Can someone fill me in on how they're supposed to work?  
> It seems like things are more intricate regarding running beam-vm-based 
> programs on a different machine than that you’re building it on.
> 
> Thanks,
> -Joe

Hey Joe,

welcome. I deploy to FreeBSD with Elixir & distillery 2.0 without any issues. 
The simple fix is to move off OSX to FreeBSD like I did and then this problem
goes away ;-).

TLDR: build your releases on the same OS+package as your deploy target.

If you unpack the .tar.gz that distillery creates, you'll see inside a ./releases/
folder. the RELEASES and *.rel and start_erl.data all specify explicit versions
of runtime and related libraries. If your Mac-based OTP release is *exactly*
the same as the FreeBSD one, *and* you have no NIFs, then it's possible
to get this working.

IMHO getting cross-compilation etc sorted isn't worth it when you can
build in a jail anyway. I then create FreeBSD packages from the distillery
release, and simply pkg-install those.

I'll write this up and post a link to it tomorrow on how to do this, it's
too long to fit in an email.

details:

1. always build releases on the same OS+arch+BEAM+packages as you
intend to deploy to. Cross-building is possible but surprisingly tricky.
If the patch versions are different, stuff may not start.

erts (Erlang RunTime System) has different patch levels and point releases.
The OTP 21 runtime on your Mac may not be the same one you're deploying
to.

The FreeBSD ones have just this week been updated and moved to a much
easier-to-update system (thanks olgeni@ ) so we should be staying pretty
up to date with official releases now. We have OTP21,22 and Elixir 1.8.2

Right now, that's 21.3.8.2 which has different modules from the original
OTP 21.0 shipped months ago -
asn1, crypto, kernel, ssl, stdlib, & more have all evolved. Your mac
built release probably won't have the same modules on it, and the release
is *very* specific about what it requires.

2. if you have NIF modules (native C code) then this definitely won't work
as the linked libraries aren't remotely compatible.

3. Every time the lang/erlang-* port is updated, you'll need to rebuild your
application (if you're not including erts).
 
A+
Dave