bake-bake-bake/bakeware: Compile Elixir applications into single, easily distributed executable binaries

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Compile Elixir applications into single, easily distributed executable binaries

The Bakeware oven

Bakeware was made over a weekend at SpawnFest 2020
and thanks to the response from the community, we’re working on finishing it
off. While it’s not ready for production, it’s definitely ready for
experimentation – just expect APIs to change in the near-term. If you’d like
to help, please let us know and stay tuned!

Bakeware extends Mix
releases with the ability
to turn Elixir projects into single binaries that can be copied and directly
run. No need to install Erlang or untar files. The binaries look and feel like
the build-products from other languages.

Here’s a quick list of features:

  • Simple – add the bakeware dependency and the Bakeware assembler to your Mix
    release settings
  • Supports OSX and Linux (We wrote the code with Windows and the BSDs in mind,
    so support for those platforms may not be far off)
  • Zstandard compression for smaller
  • Optional support for automatic software updates (work in progress)
  • Command-line argument passing conveniences
  • Lots of examples

This README contains the basics of making your applications work with Bakeware
and reference material for when you need to dig into how it works.

Since everything was written quickly and the integration is fairly
straightforward, we recommend that you take a look at the examples. The examples
are bare bones Elixir scripts, OTP applications, Phoenix applications and more
with small changes to their mix.exs files and instructions for running that
you can try out for yourself.


Mix release

Bakeware supports tieing in executable binary assembly into a Mix release
as a step by using the Bakeware.assemble/1 function.

This will assemble the necessary components to create a Bakeware executable
that can be distributed across machines to run the script/application without
extra environment setup (such as installing Elixir/Erlang, etc)

To use, add this to your release as a step after assembly:

def release do
    demo: [
      steps: [:assemble, &Bakeware.assemble/1]

Bakeware adds the following options in the release scoped to :bakeware key:

  • :compression_level – Zstandard compression level (1 to 19) where higher
    numbers generally result in better compression, but are slower to build
  • :start_command – The start script command to run when invoked. This defaults
    to "start", but can be changed to "start_iex", for example, if you want a
    prompt. See Mix.Release
    for supported commands.
def release do
    demo: [
      bakeware: [
        compression_level: 1,
        start_command: "daemon"


Bakeware supports an API similar to Erlang’s escript for implementing a main
function. Here’s an example module:

defmodule MyApp.Main do
  use Bakeware.Script

  @impl Bakeware.Script
  def main(_args) do
    IO.puts "Hello, World!"

The return value sets the scripts exit status (0 for success and other values
for errors). Other value types are supported. See
:erlang.halt/2 for how these

Next, add this module to your mix.exs‘s application description. This usually
looks something like this:

  def application do
      extra_applications: [:logger],
      mod: {Myapp.Main, []}

Why does the module get added to :mod? Everything with Bakeware operates on
OTP Releases. The macros in Bakeware.Script add the scaffolding to invoke your
main/1 function from the release.


Minimizing executable size

Bakeware binaries appear to have a lower bound of about 12 MB in size. We expect
that they can be made smaller out-of-the-box, but here are a few things you can

  1. Make sure zstd is installed to enable compression during assembly:
  • MacOS: brew install zstd
  • Ubuntu: apt-get install zstd
  1. Build using MIX_ENV=prod. The default is MIX_ENV=dev, so be sure that the
    environment variable is set.
  2. Run rm -fr _build and then mix release. During development cruft builds
    up in the release directory. Bakeware can’t tell the difference between the
    important files and the cruft, so executables will slowly grow in size if you
    don’t do a clean build.
  3. Inspect your _build/prod/rel/<name> directory and especially under lib
    for files or dependencies that you might be including on accident.
  4. Make sure that compile-time dependencies are marked as runtime: false in
    your mix.exs so that they’re not included
  5. Try raising the compression Zstandard compression level by setting
    :compression_level in the mix.exs release config

Erlang distribution

Bakeware uses Mix releases and
inherits the default of starting of Erlang distribution. If you’re using
Bakeware for commandline or other short-lived applications, this unnecessarily
starts Erlang distribution servers running and prevents two application
instances from running at a time.

To disable, run mix release.init to create starter and
env.bat.eex files in the rel directory. Then edit the files to set

Creating cross-platform binaries

Bakeware binaries include the Erlang runtime but there are still dependencies on
the host system. These include the C runtime and other libraries referenced by
the Erlang runtime and any NIFs and ports in your application. Luckily, the
binary ABIs of many libraries are very stable, but if distributing to a wide
audience, it’s useful to build on a system with older library versions. Python
has a useful pointers in their packaging

Static Compiling OpenSSL into Erlang Distribution

Sometimes wierd SSL state bugs arise with a release when openssl is not statically compiled in.
You’re affected by these ssl issues if you see things like an SSL connection being established but
after sending the first packet the remote end drops you. Attached is a Dockerfile that can be
built with Podman and used to build your baked released.

#Edit the versions of libraries in Dockerfile

#Build erlang with static openssl
podman build --tag mybuilder DockerfileFolder/

#Bake your release
podman run -it --rm -v .:/root/myproject --entrypoint bash mybuilder -c "cd /root/myproject && ./"
export MIX_ENV=prod
rm -rf _build
mix deps.get
mix release
cp _build/prod/rel/bakeware/myproject .

Building on Windows

Bakeware is tested to work in mingw environment on Windows 8 and 10. In order to setup the environment follow these steps:

  • Install chocolatey
  • Install elixir, zstandard, make, and mingw using chocolatey: choco install -y elixir zstandard make mingw
  • We need to change the default nmake used by elixir_make for Windows to make that we just installed: export MAKE=make
  • Export the CC variable as well: export CC=gcc
  • Now everything is set and the final standalone executable should get built withmix release

Reference material

Command-line arguments

In general, command-line arguments passed to Bakeware applications are passed through to Elixir. A few special command-line arguments can be passed to adjust the launchers behavior. Bakeware stops parsing command-line arguments when it encounters a --. Processed command-line arguments are not passed along to Elixir.

The following arguments may be passed:

  • --bw-info – Print out information about the application and exit
  • --bw-gc – This cleans up all unused entries in the cache (NOT IMPLEMENTED)
  • --bw-install – Unpack the application to the cache only. Do not run.
  • --bw-system-install – Install to a system-wide location (NOT IMPLEMENTED)
  • --bw-command – use the specified Mix.Release command when running the executable

Environment variables

The Bakeware launcher sets the following environment variables for use in Elixir:

Variable name Description
BAKEWARE_EXECUTABLE The absolute path to the executable
BAKEWARE_ARG1 The first command-line argument
BAKEWARE_ARGn The nth command-line argument
BAKEWARE_ARGC The number of arguments

See the Scripting section of this document for a more user friendly API.

Binary format

Bakeware application binaries look like this:

  • Bakeware application launcher
  • A CPIO archive of an Erlang/OTP release
  • Trailer

The CPIO archive can be compressed. This depends on the contents of the trailer.

Trailer format (multi-byte fields are big endian):

Offset from end Field Type Description
-4 Magic 4 byte string Set to “BAKE”
-5 Trailer version 8-bit integer Set to 1
-6 Compression 8-bit integer 0 = No compression, 1 = Zstandard
-8 Flags 16-bit integer Set to 0 (no flags yet)
-12 Contents offset 32-bit integer Offset of CPIO archive
-16 Contents length 32-bit integer Length of CPIO archive
-48 SHA1 20 bytes SHA-1 of the CPIO archive

Cache directory

Bakeware maintains a cache of extracted binaries. This is needed to run the
OTP releases and it enables start-time optimizations.

The default cache directory location is system-specific:

  • Windows – "C:/Users/<USER>/AppData/Local/Bakeware/cache"
  • MacOS – "~/Library/Caches/Bakeware"
  • Linux and other Unixes – "~/.cache/bakeware"

You can override it by setting the $BAKEWARE_CACHE environment variable.

Here’s the layout of each cache entry:

Path Created by Description
$CACHE_DIR/$SHA1/bin CPIO OTP release’s bin directory
$CACHE_DIR/$SHA1/erts-x.y.z CPIO OTP release’s ERTS
$CACHE_DIR/$SHA1/lib CPIO OTP release’s lib directory
$CACHE_DIR/$SHA1/releases CPIO OTP release’s releases directory
$CACHE_DIR/$SHA1/start CPIO Start script. E.g., bin/my_otp_release start


All code is licensed under Apache-2.0 with the exception of zstd which is dual licensed BSD/GPL. See it’s LICENSE and COPYING files for more details.

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