SSH At Scale: CAs and Principals

If you manage Linux servers over the Internet, you use SSH to connect to them. SSH lets you have a remote shell on a host over an encrypted channel so that an attacker cannot watch what you are doing over the network. In this blog post, I’m going to talk about using SSH at scale across thousands of posts.

Phase 0: Passwords

When you get started with SSH for the first time, you likely won’t have keys set up and will instead use passwords to authenticate to your servers. It will look something like this:

ssh's passsword: ********

You use SSH to connect to the server, type in your password, and you’re good to go. That’s fine for small scale, such as managing a single server, but it doesn’t come without downsides. Specifically, you won’t be able to easily use a tool such as Ansible nor do code checkins with Git.

And that’s actually a bigger problem than it sounds, because if you make it harder to use a tool, that tool will be used far less often. This can lead to things such as configuration drift due to Ansible being run less often, or giant code pushes happening once a day if Git is being run less. And giant code pushes are a particular problem, because if other engineers have written code, you’ll have to do a merge, and if a bug presents itself, you’ll now have to think back to what you did 8 hours ago, not 8 minutes ago. Having to type in a password every single time will also slow down the rate of deployment, which in turn slows down the rate of product releases. Not good.

Seriously, don’t use SSH with a password for any reason other than as a stepping step to using keys. And that brings us to…

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