[Whitestrake]

Why would a process need to run as root or have write privileges to /etc in order to automate LetsEncrypt renewals?

I run Caddy (which uses acme-go/lego as its ACME provider) as a non-root user with no access to /etc at all. It seems to be running fine.

[tedunangst]

Depends on setup, but frequently private keys are inaccessible to the web server worker process. (Which starts as root, loads keys, drops privs, etc.)

[tialaramex]

Most popular ACME (Let's Encrypt) clients allow you to provide a CSR instead of generating the keys themselves. That means a bunch more work for you, but if you're worried about this, that's what you should do. Have your safe (even manual if you insist) process make keys, make CSRs for the keys, and put those somewhere readable. The ACME client will hand them over to the CA saying "I want certs corresponding to these CSRs" without needing access to your TLS private keys at all.

[rocqua]

Using http renewal requires listening on port 80 which, by default, requires root.

[Whitestrake]

This is technically true, but contextually lacking.

acme-go/lego doesn't use HTTP validation unless you disable just about every other form of validation first. TLS-ALPN validation is much more likely, so port 443.

That said, it is very easy to allow software to bind to privileged ports without providing it root access; this has been solved for a very, very long time.

[revvx]

You can just use the web server that is already running on the machine.

You (normally) don't want downtime in your website, so you just let your regular webserver serve the acme challenge instead of stopping it.