A buildpack is a unit of work that inspects your app source code and formulates a plan to build and run your application.
Typical buildpacks are a set of at least three files:
buildpack.toml– provides metadata about your buildpack
bin/detect– determines whether buildpack should be applied
bin/build– executes buildpack logic
There is a different type of buildpack commonly referred to as a meta-buildpack. It contains only a
buildpack.toml file with an
order configuration that references other buildpacks. This is useful for
composing more complex detection strategies.
There are two essential phases that allow buildpacks to create a runnable image.
A platform sequentially tests groups of buildpacks against your app’s source code. The first group that deems itself
fit for your source code will become the selected set of buildpacks for your app. Detection criteria is specific to each
buildpack – for instance, an NPM buildpack might look for a
package.json, and a Go buildpack might look for
Go source files.
During build the buildpacks contribute to the final application image. This contribution could be as simple as setting
some environment variables within the image, creating a layer containing a binary (e.g: node, python, or ruby), or
adding app dependencies (e.g: running
pip install -r requirements.txt, or
Learn more about buildpacks by referring to the Buildpack API.