jam

jam is a command-line tool for buildpack authors and users. The jam name is simply a play on the idea of "packaging" or "packing" a buildpack.

jam comes with the following commands:

• create-stack : create a CNB stack
• help : help about any command
• pack : package buildpack
• publish-image : publish an image to a registry
• publish-stack : publish a CNB stack to a registry
• summarize : summarize buildpackage
• update-builder : update builder
• update-buildpack : update buildpack
• update-dependencies : update all depdendencies in a buildpack.toml according to metadata.constraints

The jam executable can be installed by downloading the latest version from the Releases page. Once downloaded, buildpacks can be created from a source repository using the pack command like this:

jam pack \
  --buildpack ./buildpack.toml \
  --stack io.paketo.stacks.tiny \
  --version 1.2.3 \
  --offline \
  --output ./buildpack.tgz

Building stack images on linux

In order to build stack images on linux, you will need to first install packages to enable emulation of the arm64 instruction set. This is not an issue on other operating systems (e.g. OSX) because Docker already runs in a Virtual Machine with emulation support enabled.

For example, to enable emulation on Ubuntu 2204 (Jammy), run the following command:

sudo apt-get install qemu binfmt-support qemu-user-static