At Uber, I’m currently building a self-service task execution platform, which involves getting code/artifacts from different sources, building them if necessary, and executing some commands using the artifacts.

One thing that we wanted to support is to allow users to point to a git repository, specify some build commands and a final execution command. Using JGit to clone the repository, and a ProcessBuilder to start the processes, that sounded easy.

BUT.

There’s a lot of golang services where I work, and building go services from scratch usually needs git to resolve dependencies. This was a problem for me, because like many other production environments, the infrastructure to access source control is missing in production - even for internally hosted repositories. The main problem is that the private keys needed to securely access repositories aren’t deployed to the production hosts.

The obvious (dumb?0 solution is to customize the environment setup for our service to have private keys placed within ~/.ssh/ of the production instances as part of the build process. This works, but not in a general way - it assumes that the user running the service has access to all the repos - which is definitely untrue in the cases secret projects or private repos.

This is where GIT_SSH comes in - essentially, git allows you to explicitly specify the ssh command that should be used while talking to remote repositories.

So, users can specify: GIT_SSH=team/service/git_ssh_command.sh

And the contents of git_ssh_command.sh can be something like: #!/bin/sh exec /usr/bin/ssh -o StrictHostKeyChecking=no -i /magic/location/id_rsa "$@"

And there you go! The great thing is that your glide or equivalent-go-build-tool commands will just use this automagically, and it can change this per process. That’s great for multi-tenancy in your system, and a single instance can handle multiple jobs, even if each job needs a different private key.