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+---
+title: "Releasing Elixir/OTP applications to the World"
+description: "The perils of releasing OTP applications in the wild"
+tags:
+  - "Erlang/OTP"
+  - "Elixir"
+  - "Phoenix"
+  - "Docker"
+  - "How-to"
+  - "Tips and Tricks"
+date: "2016-05-27"
+categories:
+  - "Development"
+slug: "elixir-otp-releases"
+---
+
+Developing Elixir/OTP applications is an enlightening, mind-boggling, and
+ultimately enjoyable experience. There are so many features of the language
+that change the very way we as developers think about concurrency and program
+structure. From writing pure functional code, to using message passing to
+coordinate complex systems, it is one of the best languages for the SMP
+revolution that has been slowly boiling under our feet.
+
+However, _releasing_ Elixir and OTP applications is an entirely different and
+seemingly seldom discussed topic.
+
+The distribution tool chain of Erlang and OTP is a complicated one, There's
+[`systools`][9], [`reltool`][10], [`rebar(?3)`][11], and [`relx`][12] just to
+name a few that all ultimately help in creating an Erlang/OTP ["release"][13].
+Similar to `rebar3`, [`exrm`][7] takes the high-level abstraction approach to
+combining `reltool` and `relx` into a single tool chain for creating releases of
+Elixir projects. Of course, we can also borrow from the collection of
+[autotools][14].
+
+There are plenty of articles and posts discussing how and why to use
+`exrm`. I feel many of them, however, fail to _truly_ discuss _how_ to do this
+effectively. Most will mention the surface of the issue, but never give the
+issue any real attention. As any developer that wants to eventually _ship_
+code, this is entirely too frustrating to leave alone.
+
+There are "ways" of deploying OTP code relatively simply, however, these
+methods generally avoid good practice of continuous integration/continuous
+deployment, e.g., "build the OTP application _on_ the target system" or simply
+use `mix run`, etc.
+
+I cannot speak for everyone, but my general goal is to _not_ have such a
+manual step in my release pipeline, let alone having a possibly full autotool
+chain and Erlang/Elixir stack on the production system is slightly unnerving
+for it's own set of reasons.
+
+## Problem ##
+
+Here are some selected quotes; I'm not trying to pick on anyone in particular
+or the community at large, but I'm trying to show a representation of why this
+very topic is an issue in the first place.
+
+> We need to be sure that the architectures for both our build and hosting
+> environments are the same, e.g. 64-bit Linux -> 64-bit Linux. If the
+> architectures don't match, our application might not run when deployed. Using
+> a virtual machine that mirrors our hosting environment as our build
+> environment is an easy way to avoid that problem.
+[Phoenix Exrm Releases][8].
+
+And another, similar quote:
+
+> One important thing to note, however: *you must use the same architecture for
+> building your release that the release is getting deployed to.* If your
+> development machine is OS X and you’re deploying to a Linux server, you need
+> a Linux machine to build your exrm release or it isn't going to work, or you
+> can just build on the same server you’re going to be running everything on.
+[Brandon Richey][1].
+
+Unfortunately, these miss a lot of the more subtle issues, dependency hell is
+real, and we're about to really dive into it.
+
+There are a few examples where "same architecture" isn't enough, and this is
+where we will spend the majority of our time.
+
+For these examples, we will assume our host machine is running GNU/Linux,
+specifically Arch Linux, and our target machine is running CentOS 7.2. Both
+machines are running the `AMD64` instruction sets, the architectures are the
+_same_.
+
+### Shared Objects ###
+
+Let's start with the most simplistic issue, different versions of shared
+objects.
+
+Arch Linux is a rolling release distribution that is generally _right_ on the
+bleeding edge of packages, upstream is usually the development sources
+themselves. When `ncurses` moves version 6, Arch isn't far behind in putting it
+in the stable package repository (and rebuilding a number of packages that
+depend on `ncurses`). CentOS, on the other hand, is not so aggressive.
+Therefore, when using the default `relx` configuration with `exrm`, the Erlang
+runtime system (ERTS) bundled with the release _will_ be incompatible with the
+target system.
+
+When the OTP application is started, an obscure linking error will be emitted
+complaining about how ERTS cannot find a `ncurses.so.6` file and promptly fail.
+
+Worse, after possibly "fixing" this issue, `ncurses` is only one of a few
+shared objects Erlang needs to run, depending on what was enabled when Erlang
+was built or what features the deployed application needs.
+
+### Erlang Libraries ###
+
+We may try to resolve this issue by adding a particular `rel/relx.config` file
+to our Elixir project. Specifically, we will _not_ bundle ERTS, opting to use
+the target's ERTS instead.
+
+    {include_erts, false}.
+
+This seems like a promising approach, until another error message is emitted at
+startup, namely, ERTS cannot find `stdlib-2.8` in the `/usr/lib/erlang/lib`
+folder.
+
+Did I mention that our current build system is Arch and our target is CentOS?
+Arch may have the _newest_ version of Erlang in the repository and CentOS is
+still at whatever it was at before: R16B unless the [Erlang Solutions][1]
+release is being used.
+
+Since Erlang applications do (patch number) version locking, applications in
+the dependency tree will need to match exactly and it's guaranteed that any and
+all OTP applications will be at least depending on the Erlang kernel and the
+Erlang standard library, these are at least two OTP applications _our_
+application is going to need that are *no longer packaged when `relx` doesn't
+bundle ERTS*.
+
+Even if we specify another option to `relx`, namely, `{system_libs, true}.`, we
+are left with the same lack of Erlang system libraries.
+
+That's correct and there is some sensible reasons for this. If we ask `exrm`
+and therefore `relx` to not include the build system's ERTS, we are _also_
+excluding the standard Erlang libraries from the release as well, asking to
+include the standard libraries of the build system's ERTS could run into the
+_very_ same issues as above for a whole host of other reasons.
+
+We are left to attempt more solutions.
+
+### Docker or Virtualization ###
+
+Next, since we do want to ultimately get our build running in a CI/CD
+environment, we may look toward virutalization/containerization. Being sensible
+people, we try to use a small image, maybe basing our image on [Alpine
+Linux][2] as to be nice to our precious `/var` or SSD space. We may even go so
+far as to build Erlang and Elixir ourselves in these images to make sure we
+have the most control over them as we can. Furthermore, since we are building
+everything ourself, shipping the built ERTS seems like a good idea too, so we
+can delete the `rel/relx.config` file.
+
+This seems promising. However, we have shared object problems again. Since we
+are building Erlang and Elixir ourselves, we decided to disable `termcap`
+support thus no longer requiring the `ncurses` library altogether. We hope that
+the `openssl` libraries are the same, so we don't have to worry about that
+mess, and we move on.
+
+This time, when we attempt to deploy the application get a different, obscure
+error: something about our `musl` C library isn't found on the target system.
+Right, because we are trying to create a small image, we opted to use the
+`musl` C library because of it's size and being easily supported in the Alpine
+Linux container. Trying to use GNU C library is too cumbersome and would only
+inflate the image beyond any gains we would achieve by using Alpine in the
+first place.
+
+That's not going to work.
+
+### OTP as Project Dependency ###
+
+Another option we might try is make Erlang a build dependency of our Elixir
+application, this _could_ be achieved via the following structure:
+
+    {:otp,
+     "~> 18.3.2",
+     github: "erlang/otp",
+     tag: "OTP-18.3.2",
+     only: :prod,
+     compile: "./otp_build autoconf;" <>
+              "./configure --without-termcap --without-javac;" <>
+              "make -j4" <>
+              "DISTDIR=/tmp/erlang make install"
+    }
+
+Then using `rel/relx.config` with:
+
+    {include_erts, "/tmp/erlang"}.
+
+*May* turn out to work, assuming the build server and the target system have
+the same shared objects for OpenSSL and others that may be enabled by default.
+
+> However, I didn't follow this idea all the way to the end as I wasn't
+> entirely happy with it, and it would fall to some later issues.
+
+Notably, though, this will inflate the production builds drastically since our
+`mix deps.get` and `mix deps.compile` steps will hang attempting to build
+Erlang itself.
+
+However, again, we will likely run into issues with the C library used by the
+build system/container. Going this route doesn't allow us to use Alpine Linux
+either.
+
+Worse, there's another issue that hasn't even shown itself but is lying in
+wait: native implemented (or interface) functions (NIFs).
+
+If our project has a dependency that builds a NIF as part of its build
+(Elixir's [comeonin][16] is a good example of this), unless the NIF is
+statically compiled, we are back to square one and shared objects are not our
+friends. Furthermore, if we are using a different standard library
+implementation, i.e., `musl` vs `glibc`, the dependency will likely complain
+about it as well.
+
+## Non-Solution Solutions ##
+
+Of course, all of these above issues can be solved by "just building on the
+target machine" or by simply using `mix run` on the target instead. However, I
+personally find these solutions unacceptable.
+
+I'm not overly fond of requiring my target hosts, my production machines,
+running a full development tool chain. Before this is dismissed as a personal
+issue, remember that our dependency tree may contain NIFs outside of our
+control. Therefore, it's not just Erlang/Elixir that are required to be on the
+machine, but a C standard library and autotools too.
+
+This solution doesn't immediately give the impression of scaling architecture.
+If a new release needs to be deployed, each server will now need to spare some
+load for building the project and its dependencies before any real, actual
+upgrading can continue.
+
+## Solutions(?) ##
+
+What are we to do? How are we to build Erlang/Elixir/OTP applications as part
+of our CI/CD pipeline? Particularly, how are we to build our applications on a
+CI/CD system and *not* the production box(es) themselves?
+
+If any of the above problems tell us anything, it's that the build system must
+be either the *exact same* machine or clone with build tools. Thankfully, we
+can achieve a "clone" without too much work using [Docker][3] and the [official
+image registries][4].
+
+By using the official CentOS image and a specific tag, we can match our target
+system almost exactly. Furthermore, building the Erlang/Elixir stack from
+source is a relatively small order for a Docker container too, making
+versioning completely within reach. Moreover, since the build host and the
+target host are nearly identical, bundling ERTS should be a non-issue.
+
+> This is the observed result of using [docker-elixir-centos][5] for a base
+> image for CI builds.
+
+Another possible solution is to ship Docker containers as the artifact of the
+build. However, this, to do well, requires a decent Docker capable
+infrastructure and deployment process. Furthermore, going this route, it's
+unlikely that `exrm` is even necessary at all. It is likely more appropriate to
+simply use `mix run` or whatever the project's equivalent is. Another thing
+lost here, is [relups][6], which is essentially the whole reason of wanting to
+use `exrm` in the first place.
+
+As such, if using `exrm` is desired, setting up a build server will be
+imperative to building reliably and without building on production. Scaling
+from a solid build foundation will be much easier than building and "deploying"
+on the production farm itself.
+
+## Moving Forward ##
+
+Releasing software isn't in a particularly hard class of problems, but it does
+have its challenges. Some languages attempt to solve this challenge in its
+artifact/build result. Other languages, unfortunately, don't attempt to solve
+this problem at all. Though, I can see it possible to eventually reach a goal
+of being able to create binary releases with steps as simple as `./configure &&
+make && make install && tar`.
+
+But we aren't there yet.
+
+But we are close.
+
+The current way Erlang/OTP applications want to be deployed includes wanting to
+ship _with_ the runtime, this is a great starting point.
+
+To move to a better, easier release cycle, we need a few things:
+
+*   The ability to (natively) cross-compile to different architectures and
+    different versions of ERTS _and_ cross-compile Erlang code itself.
+
+*   The ability to easily statically compile ERTS and bundle the result for the
+    specified architecture.
+
+Cross-compiling to different versions of ERTS is likely a harder problem to
+tackle. But being able to cross-compile the ERTS itself is likely much easier
+since this is already a [feature][15] of GCC.
+
+Thus, our problem is now how do we add and/or expose the facility of
+customizing the appropriate build flags to our projects and dependencies to
+cross-compile a static ERTS and any NIFs and bundle these into a solid OTP
+release.
+
+[1]: https://erlang-solutions.com
+
+[2]: http://alpinelinux.org
+
+[3]: https://docker.com
+
+[4]: https://hub.docker.com/explore/
+
+[5]: https://github.com/kennyballou/docker-elixir-centos
+
+[6]: http://erlang.org/doc/man/relup.html
+
+[7]: https://github.com/bitwalker/exrm
+
+[8]: http://www.phoenixframework.org/docs/advanced-deployment
+
+[9]: http://erlang.org/doc/man/systools.html
+
+[10]: http://erlang.org/doc/man/reltool.html
+
+[11]: https://github.com/erlang/rebar3/releases
+
+[12]: https://github.com/erlware/relx
+
+[13]: http://erlang.org/doc/design_principles/release_structure.html
+
+[14]: https://en.wikipedia.org/wiki/GNU_Build_System
+
+[15]: https://www.gnu.org/software/automake/manual/html_node/Cross_002dCompilation
+
+[16]: https://hex.pm/packages/comeonin