Higher Order Heroku

Developing on Heroku

Subscribe to the Heroku Weekly to get the best of the Heroku community in your inbox. Every weekish.
Submit a link for inclusion on Higher Order Heroku and in the Heroku Weekly.

Building Dependency Binaries for Heroku Applications

By Peter Braswell on July 10, 2012

Managing an application's code dependencies, once a source of constant pain and conflict, is now a solved problem in most modern languages. Ruby has Bundler, Node.js has npm, Python has pip, Clojure has Leiningen… the list continues.

What remains unsolved is how to declare and manage system-level dependencies -- external binaries on which your application is dependent. This article explores explicitly managing and building system-level dependencies using the Vulcan build server.


It's common for an application to shell out to a local executable to perform some computationally intense work where compiled libraries are more performant or robust. Examples include Ghostscript, which your application might use to manipulate PDF or PostScript files and ImageMagick for resizing and cropping uploaded images.

Many deployment services attempt to fill this need by providing a set of common binaries bundled into every environment. This is a fragile approach that boxes you in to out-dated or incompatible library versions.

Having the ability to install system-wide binaries in your deployment environment is also poor solution. It merely shifts the burden of dependency management from the service provider to you, the application developer.

Twelve-factor is firm in its stance on system-level dependencies:

Twelve-factor apps also do not rely on the implicit existence of any system tools... While these tools may exist on many or even most systems, there is no guarantee that they will exist on all systems where the app may run in the future, or whether the version found on a future system will be compatible with the app. If the app needs to shell out to a system tool, that tool should be vendored into the app.


Vendoring a binary dependency requires that the binary be built specifically for the remote environment's operating system and processor architecture. Even with the benefits of virtual machine software this is a non-trivial task for developers.

A better solution is to use the remote environment of your service provider to compile and build the required dependencies. Such a process loosely adheres to the following steps:

  1. Specify the required library's source
  2. Get a remote shell to your production environment
  3. Download the library source in the remote shell
  4. Compile the library remotely
  5. Download the compiled library for use in your application's source-tree

While this process is not a lengthy one, your eye should spot that steps 2-5 are ripe for automation. That's where Vulcan comes in.

Vulcan is a utility that bundles and uploads a source-tree to a remote environment, runs the necessary compilation commands on the source tree, and downloads the resulting binary -- all in a single command. Vulcan consists of a Ruby-based CLI and Node.js server and, though built by and for Heroku, is platform-agnostic.


Installing the Vulcan CLI is simply a matter of installing the vulcan gem:

These steps assume you have git and ruby available from the command line and have already signed up for a Heroku account. The Heroku Toolbelt can get you up and running if you're missing any components.

$ gem install vulcan
Please run 'vulcan update' to update your build server.
Successfully installed vulcan-0.7.1
1 gem installed

Vulcan's build-server is a simple Node.js app that runs in the same target environment your application will be deployed. If your app runs on Heroku, Vulcan can deploy itself to Heroku with vulcan create appname.

You will need a verified Heroku account before running this command as Vulcan requires the use of a (free) add-on.

$ vulcan create buildserver-you
Creating buildserver-you... done, stack is cedar
http://buildserver-you.herokuapp.com/ | git@heroku.com:buildserver-you.git
Initialized empty Git repository in /private/var/folders/Uz/UzRCgjzkGIi7Iqz9QNi6NUDrHf6/-Tmp-/d20120614-31875-1qjw1d6/.git/
Counting objects: 883, done.

-----> Heroku receiving push
-----> Node.js app detected
       Dependencies installed
-----> Discovering process types
       Procfile declares types -> web
-----> Compiled slug size is 4.1MB
-----> Launching... done, v3
       http://buildserver-you.herokuapp.com deployed to Heroku

The Vulcan build server is now running on Heroku at http://buildserver-you.herokuapp.com as a (free) single-dyno app. It's important to note there's nothing blessed about Vulcan running on Heroku. It's just a normal application running in user-space, giving you all the visibility and management tools you're used to.

If you've manually deployed the build server to another provider you'll need to set its location so the CLI knows where to send build tasks. This is done by setting the VULCAN_HOST env var: $ export VULCAN_HOST=http://myserver.domain.com..


The Ghostscript library utilized in the processing PDF files tutorial on the Heroku Dev Center makes for a good example of building a binary application dependency.

Download source

First, download and expand the Linux x86 64-bit source for the Ghostscript project. At the time of this writing it is located at http://downloads.ghostscript.com/public/binaries/ghostscript-9.05-linux-x86_64.tgz.

For the purpose of this article Heroku will be assumed to be the target environment. Heroku's dynos run on 64-bit Linux kernel. If your target environment differs you will need to select the correct source distribution.

$ wget http://downloads.ghostscript.com/public/ghostscript-9.05.tar.gz
$ tar -xvzf ghostscript-9.05.tar.gz 
x ghostscript-9.05/
x ghostscript-9.05/base/
x ghostscript-9.05/base/szlibxx.h

You now have a Ghostscript source directory at ./ghostscript-9.05.

Remote compilation

Next, use the Vulcan CLI to initiate a build task on the build server with vulcan build. This will send the source to the target environment for compilation. The only required argument is -s, the location of the Ghostscript source directory. The -v flag (verbose) will show the output from the compilation process and is recommended as, depending on the library, compilation can take some time and it's useful to see its progress.

$ vulcan build -v -s ./ghostscript-9.05
Packaging local directory... done
Uploading source package... done
Building with: ./configure --prefix /app/vendor/ghostscript-9 && make install
checking for gcc... gcc
checking whether the C compiler works... yes
>> Downloading build artifacts to: /tmp/ghostscript-9.tgz
   (available at http://buildserver-you.herokuapp.com/output/45380fa6-e02a-479b-a7af-d9afb089b81f)

On completion of the build process the resulting binaries are packaged and downloaded for you. In this example the binary package can be found locally at /tmp/ghostscript-9.tgz and remotely at http://buildserver-you.herokuapp.com/output/45380fa6-e02a-479b-a7af-d9afb089b81f.

Although the Vulcan source indicates the ability to fetch source packages directly from a URL (i.e. $ vulcan build -s http://downloads.ghostscript.com/public/ghostscript-9.05.tar.gz this tends to result in build errors. At this time the most reliable method is to manually download and expand the source before passing to vulcan.


Looking at the output from the Ghostscript example you can see that a sensible autoconf-based command is chosen for you: ./configure --prefix /app/vendor/ghostscript-9 && make install. If you need to specify a non-default build command you can do so with the -c flag. Here is an example adding the --without-ssl configure option when building wget.

$ vulcan build -v -s ./wget-1.13 -c "./configure --prefix /app/vendor/wget-1.13 --without-ssl && make install" -p /app/vendor/wget-1.13
Packaging local directory... done
Uploading source package... done
Building with: ./configure --without-ssl && make install
configure: configuring for GNU Wget 1.13
>> Downloading build artifacts to: /tmp/wget-1.tgz
   (available at http://buildserver-you.herokuapp.com/output/66ba3e2b-77ef-4409-acc2-fca70650c318)

The -p (prefix) flag is also used here to tell Vulcan where to look on the build server for the compiled artifacts (/app/vendor/wget-1.13). To avoid ambiguities it's best to specify this value and to set it to the same value as the --prefix flag passed to ./configure.


Once you have a binary appropriate for use on Heroku you need to vendor it within your application. Though conventions vary by language the approach taken is similar across them all. Vendoring the wget executable is a straight-forward process.

Create a vendor directory that will house the wget binary and copy in the executable from the vulcan build results.

$ mkdir -p vendor/wget/bin
$ cp /tmp/wget-1/bin/wget vendor/wget/bin/

The null buildpack can be used to test wget in isolation. Create a Heroku app that consists only of this vendor directory and specify the null buildpack.

$ git init
$ git add .
$ git commit -m "Vendored wget"

$ heroku create --buildpack https://github.com/ryandotsmith/null-buildpack
Creating severe-water-5643... done, stack is cedar
http://severe-water-5643.herokuapp.com/ | git@heroku.com:severe-water-5643.git
Git remote heroku added

Add vendor/wget/bin to the app's PATH and deploy it to Heroku.

$ heroku config:add PATH=vendor/wget/bin:/usr/bin:/bin
Setting config vars and restarting severe-water-5643... done, v6
PATH: vendor/wget/bin:/usr/bin:/bin

$ git push heroku master
-----> Heroku receiving push
-----> Fetching custom buildpack... done
-----> Null app detected
-----> Nothing to do.
-----> Discovering process types
       Procfile declares types -> (none)
-----> Compiled slug size is 172K
-----> Launching... done, v4
       http://severe-water-5643.herokuapp.com deployed to Heroku

To git@heroku.com:severe-water-5643.git
 * [new branch]      master -> master

To test that the compiled version of wget works use a one-off dyno to run a test command:

$ heroku run wget http://www.google.com/images/logo_sm.gif
Running wget http://www.google.com/images/logo_sm.gif attached to terminal... up, run.1
HTTP request sent, awaiting response... 200 OK
Length: 3972 (3.9K) [image/gif]
Saving to: 'logo_sm.gif'

100%[=============================================================>] 3,972       --.-K/s   in 0s

2012-07-10 14:48:48 (200 MB/s) - 'logo_sm.gif' saved [3972/3972]

The command was successfully invoked on Heroku using the vulcan-compiled wget executable and the output (but not the fetched file) was streamed to your local shell.


There are several utilities available to you to introspect the remote compilation process.


Outside of using the -v flag to force see the build output you can also use the logs of the Vulcan build server to gain better visibility into the process. Since the Vulcan build server is just a Node.js app running in your target environment this is a trivial task. On Heroku use heroku logs and the -a flag with the name of your build server app.

$ heroku logs -t -a buildserver-you
2012-07-04T15:29:20+00:00 app[web.1]: [7f3a7510-400a-44d4-9132-66a2e6c878a5] spawning build
2012-07-04T15:29:20+00:00 app[web.1]: valid socket
2012-07-04T15:29:21+00:00 heroku[run.1]: Awaiting client
2012-07-04T15:29:21+00:00 heroku[run.1]: Starting process with command `bin/make "7f3a7510-400a-44d4-9132-66a2e6c878a5"`
2012-07-04T15:29:22+00:00 heroku[run.1]: State changed from starting to up
2012-07-04T15:30:10+00:00 heroku[run.1]: Process exited with status 1
2012-07-04T15:30:10+00:00 heroku[run.1]: State changed from up to complete

By default Vulcan will spawn a on-off dyno to perform the build command. This is evident by the run.1 dyno in the log output. In some circumstances this can result in a billable event if your web and one-off dyno usage combined exceeds 750 hours for any one month.

If this small overage is meaningful to you you can sacrifice compilation concurrency and force Vulcan to execute the compilation command in-process with the SPAWN_ENV config var.

$ heroku config:add SPAWN_ENV=local -a buildserver-you
Setting config vars and restarting buildserver-you... done, v11
SPAWN_ENV: local

The build command will then execute within the web process:

$ heroku logs -t -a buildserver-you
2012-07-04T15:35:43+00:00 app[web.1]: [bbeab2b8-3941-4d41-94af-24c4f0fa65c0] spawning build
2012-07-04T15:36:33+00:00 app[web.1]: - - [Wed, 04 Jul 2012 15:36:33 GMT] "GET /output/bbeab2b8-3941-4d41-94af-24c4f0fa65c0 HTTP/1.1" 200 - "-" "Ruby"
2012-07-04T15:36:33+00:00 heroku[router]: GET buildserver-you.herokuapp.com/output/bbeab2b8-3941-4d41-94af-24c4f0fa65c0 dyno=web.1 queue=0 wait=0ms service=35ms status=200 bytes=75

While this fails to adhere to the background job pattern it may be acceptable for your use-case.

Remote shell

If a build fails it is often useful to be able to view the failed artefacts. Since Vulcan performs its work in temporary directories their contents are cleaned up after each build. However, a remote shell can be used to manually invoke the build command and navigate the build results.

At the start of every build request Vulcan outputs log statements resembling the following:

2012-07-04T18:57:10+00:00 app[web.1]: [6869e68a-492d-4a7e-8b27-64352811d7dc] saving to couchdb
2012-07-04T18:57:10+00:00 app[web.1]: [6869e68a-492d-4a7e-8b27-64352811d7dc] saving attachment - [id:6869e68a-492d-4a7e-8b27-64352811d7dc rev:1-722a96f6734a3511efd73b7cfb9a2aed]

The attachment id, here 6869e68a-492d-4a7e-8b27-64352811d7dc, is all that's needed to manually invoke the build yourself. Establish a remote shell to the Vulcan build server environment. On Heroku you can use heroku run bash:

$ heroku run bash -a buildserver-you
~ $

Then invoke the bin/make command with the attachment id. You will see the output of the build process and can then browse the output directory yourself.

$ bin/make "6869e68a-492d-4a7e-8b27-64352811d7dc"
configure: configuring for GNU Wget 1.13
checking for a BSD-compatible install... /usr/bin/install -c
checking whether build environment is sane... yes
$ cd /app/vendor/wget-1.13


Updating Vulcan is simple. Update the CLI using ruby gems:

$ gem install vulcan
Please run 'vulcan update' to update your build server.
Successfully installed vulcan-0.8.0
1 gem installed

And use the vulcan update command to update the build server.

Be aware that updating the build server while active compilations are running will cause them to be aborted.

$ vulcan update
Initialized empty Git repository in /private/var/folders/tt/7f38d4b14qq5xglpj3yl0smr0000gn/T/d20120704-53816-m4n0rn/.git/
Counting objects: 883, done.

-----> Heroku receiving push
-----> Node.js app detected
-----> Resolving engine versions
       Using Node.js version: 0.6.18
       Using npm version: 1.1.4
-----> Launching... done, v15
       http://buildserver-you.herokuapp.com deployed to Heroku

To git@heroku.com:buildserver-you.git
 + a5f27be...a934704 master -> master (forced update)


Invalid secret

If working across multiple development environments or some other non-default workflow you may see the following build server error logged when attempting to invoke a build:

2012-07-04T17:39:47+00:00 app[web.1]: [672b5df6-ad8c-49ed-9831-515207e2dc4f] ERROR: invalid secret
2012-07-04T17:39:47+00:00 app[web.1]: invalid secret

This occurs when the CLI secret hash, created when the build server was created with vulcan create, either doesn't exist or doesn't match the server-side secret. The most common cause is that the ~/.vulcan configuration file doesn't exist in your environment. You can create it with the following contents:

:app: buildserver-you
:host: buildserver-you.herokuapp.com
:secret: reallylonghash12df

If you don't have access to your original .vulcan file you can find your secret on Heroku using heroku config:

$ heroku config:get SECRET -a buildserver-you

Copy your ~/.vulcan file to each development machine from which you wish to invoke builds.

Heroku binaries

During the course of writing this article the following binaries were compiled for use on Heroku.

If you'd like to list a Heroku binary here, please send a pull request.

Library Build command Binary Contributor
GNU Wget v1.13 vulcan build -v -s ./wget-1.13 -c "./configure --prefix /app/vendor/wget-1.13 --without-ssl && make install" -p /app/vendor/wget-1.13 download @rwdaigle
ImageMagick v6.7.8-1 vulcan build -v -s ./ImageMagick-6.7.8-1 download @rwdaigle
Ghostscript v9.05 vulcan build -v -s ./ghostscript-9.05 download @rwdaigle