Apt - Minimum Viable Buildpack - 03 - Installed Packages Layer

[colincasey]

The Debian packages that we download need to be extracted into a target folder. This folder can be cached and several environment variables will refer to this location so that downloaded libraries and tools can be made available to subsequent buildpacks. So, for this, we'll introduce two layers:

• InstalledPackagesLayer - the cacheable folder where all packages will be installed.
• EnvironmentLayer - a layer which sets the environment variables pointing to the installed packages which is always recreated.

Caching

Caching for the InstalledPackagesLayer is controlled by two values:

• the contents of the Aptfile (parsed, not raw)
• the os and arch of the system the buildpack is executing in

Environment Variables

The EnvironmentLayer prepends the following paths to their respective environment variables:

• PATH
  • <layer_dir>/bin
  • <layer_dir>/usr/bin
  • <layer_dir>/usr/sbin
• LD_LIBRARY_PATH / LIBARY_PATH
  • <layer_dir>/usr/lib/x86_64-linux-gnu (if the arch is amd64)
  • <layer_dir>/usr/lib
  • <layer_dir>/lib/x86_64-linux-gnu (if the arch is amd64)
  • <layer_dir>/lib
• INCLUDE_PATH / CPATH / CPPPATH
  • <layer_dir>/usr/include/x86_64-linux-gnu (if the arch is amd64)
  • <layer_dir>/usr/include
• PKG_CONFIG_PATH
  • <layer_dir>/usr/lib/x86_64-linux-gnu/pkgconfig (if the arch is amd64)
  • <layer_dir>/usr/lib/pkgconfig

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• ⬆️ Apt - Minimum Viable Buildpack - 02 - Aptfile Parsing #2
• ⬇️ Apt - Minimum Viable Buildpack - 04 - Install Packages #8

[edmorley]

In case it helps you plan - I'm not going to have time to review this today unfortunately. I might be able to tomorrow. If you were otherwise blocked and didn't have something to work on - one of the questions I'll have during the review (either to ask or to look into myself), is whether there are any parts of the deb downloading/extracting strategy from the classic APT buildpack that can be done a more elegant way (ie: not using dpkg) - eg researching if in the last N years apt has added any more install options we could use etc. Have you had a chance to do any research in that area?

[colincasey]

@edmorley so the situation with apt and dpkg doesn't seem to have improved at all when it comes to non-admin installation of packages. There are alternative package managers which may be worth investigating (such as Nix) but I considered those alternatives to be outside the scope of this buildpack work.

[schneems]

Thanks a ton for working on this. I made some suggestions, comments and requests. See individual comments for more.

[schneems]

A few real quick suggestions. I'm not done reviewing the new commit

[schneems]

Thanks for incorporating prior changes. I think this looks good. I've moved over to 04

[edmorley]

I hadn't reviewed this :-(

[colincasey]

Sorry, I didn't realize I was still waiting on you here @edmorley.