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heroku-buildpack-xmlsec

A buildpack for installing xmlsec1 on Heroku

Usage

You may need to use this buildpack in conjunction with another; use the heroku cli

heroku buildpacks:add https://github.com/uktrade/heroku-buildpack-xmlsec#1.2.26

or use the heroku admin website to add that buildpack.

Once xmlsec1 is installed via the buildpack you can run it with:

heroku run xmlsec1

Why Fork

Security

Minimise Surface Area

This fork of a fork is because we didn't want to download a binary from someone else's s3 bucket. Instead we're compiling our own binary and including it in the buildpack.

Ability to quickly update

If there are any security vulnerabilities we should be in the position to deploy an updated version without relying on third-parties.

Ease of switching Heroku stacks

If we want to change the stack from heroku:16-build to a newer stack we can update our Dockerfile to build from the correct image provided by Heroku.

How it works

We are building the binary from source, this is slightly complicated because the binary will be running inside of Heroku so if we build on a developer's machine then there is no guarantee that any shared libraries the compiler links to will be the same in Heroku.

To get around this we are building in a Docker image that is based on the Heroku heroku:16-build image, our image then downloads the source tarball for xmlsec1 and compiles it then tar's the output to stdout. This is redirected into a file outside of the docker container and into the local filesystem as xmlsec.tar.gz this file is committed into the repo.

But committing binaries into a repo is an anti-pattern

Yes but this means we don't need to have a CI pipeline pushing the tarball somewhere like Amazon S3 and this isn't really a repository of code, we're not really using it for source control. It's a git repo because that's what Heroku wants custom buildpacks to be.

The downside of this is that it expects you to have Docker installed locally.

How to update the binary

$ export VERSION=1.2.26 # or whatever the version you want to build
$ git rm *.sig
$ make build
$ make release
$ git add xmlsec* README.md
$ git commit -m "update to version $VERSION"
$ git tag -a $VERSION -m "update to $VERSION"
$ git push --follow-tags

Then update your heroku application to use the buildpack with the tag you just set e.g:

https://github.com/uktrade/heroku-buildpack-xmlsec#1.2.26