OTP Version Mismatch

I’m using a Docker image that has Erlang/OTP 20. If I use a version of Elixir compiled with OTP 19, can I expect the same bytecode output when I compile my dependencies, as if I had an Elixir compiled with OTP 20?

I want to make sure I don’t have any issues when my Elixir version was compiled with a different OTP version than my system is running.

Elixir compiled with OTP19 should work on OTP20 (else it’s a bug), however not the reverse.

Is only 1 version difference supported, or all future versions? 19 -> 20 is ok, how about 19 -> 21, etc?

No you can’t! Elixir does on its own compile time a feature selection based on the OTP/ERTS that is compiling the elixir.

When elixir is compiled on OTP 19 it will not generate code that uses 20s features. But if such an elixir is running under an 20 run time the byte code it will spit out will be for OTP 20.

I hope you get what I mean… Hard to describe…

Ps: byte code is generated by the Erlang compiler. Elixir compiles into a subset of Erlang which is called Erlang core.

Of course yep, OTP20 features will be missing from an Elixir with OTP19, like color coded diff errors and such as one of a few examples. :slight_smile:

So this feature stuff and the fact that actually erlc will generate the byte code results in the fact, that elixir compiled on 19 and 20 won’t generate the same byte code from same input.

But any module compiled on OTP X should also run on OTP X + Y with Y beeing an element of N.

while it should work going that way…

I would really recommend absolute dev/staging/production parity - even so pedantic down to exact patch version…

you can use something like https://github.com/asdf-vm on your dev box to install the appropriate versions on a per project level…


Yep and if you want to install Elixir compiled with a certain (major) version of Erlang with asdf, you can do something like asdf install elixir 1.6.0-otp-20 :slight_smile:

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Thanks, everyone! It looks like asdf uses Elixir bulids precompiled by Bob. How reliable are those builds? Are they officially supported?

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Bob is as official as anything from the hex-team. And you can also build from elixir and Erlang directly from git, by tag, branch, or sha, but as I’m on mobile I can’t lookup the necessary syntax right now. But I remember it was only documented as a generic feature of asdf and not in the asdf exixir plugin repository.