The HOSTALIASES feature works well when combined with wildcard host definitions in SSH config

I run my own DNS locally via Pi-hole, but I also like to have SSH configuration to specify various options depending on the hosts I'm remotely connecting to. Usually it's the username to use, sometimes it's whether I want to do X11 forwarding, and so on.

Problem

My work machines have very odd and hard to remember hostnames. I could use the SSH configuration feature (via the .ssh/config file) to get around this, like this:

Host easy
    HostName hard-to-remember
    User username-to-use

Then I could just remotely connect to that hard-to-remember host machine like this:

ssh easy

(As a bonus, having securely shared public key credentials with ssh-copy-id beforehand makes this process even smoother.)

But I don't want to expose those hard-to-remember work machine hostnames in the configuration.

Hello HOSTALIASES

I learned today about the HOSTALIASES environment variable which is supported by glibc's resolver function gethostbyname(). Pointing HOSTALIASES to a file of "aliasname realname" pairs of hostnames means that commands that use gethostbyname() to resolve hostnames can be given alias hostnames instead of real hostnames. The ssh command uses that function.

Solution

This is what I did:

First, I created a file host.aliases (making sure not to check this file into a git repo, by adding the file name to .gitignore) with content like this:

oldmbp realsecrethostname1
newmbp anothersecretworkhostname

Then, in my .bashrc, I set the HOSTALIASES environment variable to point to this file:

export HOSTALIASES="$HOME/.dotfiles/host.aliases"

Finally, I modified the contents of my .ssh/config file to use wildcards matching the aliases:

Host *mbp
    User username-to-use

That way I can use easy and memorable hostnames when connecting to my work machines (e.g. ssh oldmbp) without exposing the hostnames in any public configuration.