Heroku buildpack for OpenCV

Steve Marschner, February 2016

This buildpack provides a basic installation of OpenCV that can be used to compile C++ code in later buildpacks and run it in the application. In particular, it is designed to support C++ addons compiled by the standard Node.js buildpack.

The buildpack works by unpacking an image of OpenCV that is stored on S3, and setting up the required environment variables for it to be used by later buildpacks and at run time.

Creating the OpenCV image

The image is created by building OpenCV from source in a Heroku one-off shell running in an app that has the Python buildpack installed. This is set up by running:

heroku create --buildpack https://github.com/computationaltextiles/ct-buildpack-python-opencv.git
heroku config:set AWS_ACCESS_KEY_ID=<key>
heroku config:set AWS_SECRET_ACCESS_KEY=<secret>
git push heroku master
heroku run bash

Then the build is performed (TODO: make this a script). Then the opencv directory, plus the files it adds to the Python directory, is tarred up and uploaded to S3. The following commands are what I used:

pip install numpy
wget https://github.com/Itseez/opencv/archive/2.4.11.zip
unzip 2.4.11.zip && rm 2.4.11.zip
wget https://cmake.org/files/v3.5/cmake-3.5.0-rc1-Linux-x86_64.tar.gz
tar zxf cmake-3.5.0-rc1-Linux-x86_64.tar.gz && rm cmake-3.5.0-rc1-Linux-x86_64.tar.gz
mkdir .heroku/cmake
mv cmake-3.5.0-rc1-Linux-x86_64/bin .heroku/cmake
mv cmake-3.5.0-rc1-Linux-x86_64/share .heroku/cmake
cd opencv-2.4.11/
../.heroku/cmake/bin/cmake -DCMAKE_INSTALL_PREFIX=/app/.heroku/opencv .
make
make install
cd ..
tar zcf opencv.env.tgz .heroku/opencv .heroku/cmake .heroku/python/lib/python2.7/site-packages/numpy .heroku/python/lib/python2.7/site-packages/cv*
aws s3 cp opencv.env.tgz s3://test5a9c0284/runtimes/opencv.env.tgz

Then I set that file to be public via the S3 console, since the buildpack just downloads it without any credentials.

For now this is a bare-bones OpenCV 3.1.0 build that is just whatever it was able to compile without downloading any dependencies.

TODO

I would also like to be able to install this buildpack after the standard Python buildpack, so that the OpenCV Python modules are installed for use in Python code. I believe this will require working out what OpenCV installs into the Python directories and including that in the package.

The image should be stored in a project-owned S3 bucket and downloaded using appropriate credentials rather than an anonymous download.