Julia Evans

Day 53: a little nginx, IPv6, and wireguard

I spent the day on Wednesday trying to run my puzzle thing on fly.io. I got part of the way there and learned a few things along the way:

miscellaneous IPv6 learning

I’d never really used IPv6 before, and I learned that IPv6 address are often in square brackets. For example to get rails to listen on IPv6 addresses, I had to run:

CMD ["rails", "server", "-b", "[::]"]

CMD ["rails", "server", "-b", ""] will only listen on IPv4 addresses!

But you don’t always seem to need square brackets, for example I ssh’d to an IPv6 address like this:

ssh fdaa:0:bff:a7b:aa4:4c98:4224:2

I think the rule might be that you need to use square brackets if you’re going to include a port, like fade::5 port 53 is [fade::5]:53, because otherwise it would be ambiguous whether the port is part of the IP address or not.

how to make nginx re-resolve DNS every time

I learned that if you do

proxy_pass http://some-website.com:2000;

in an nginx configuration, nginx will resolve some-website.com to an IP address once when it boots, and then never update again. This was not good because the IP addresses of my backends were changing all the time, so I needed to figure out how to get nginx to re-resolve DNS.

Instead I needed to do something like this:

location @rails {
    resolver [fdaa::3];
    set $backend "http://rails.internal:8080";
    proxy_pass $backend;

It turns out that if you proxy_pass to something with a variable with it, nginx will resolve DNS. You also need to set a DNS server to use explicitly, nginx won’t use what’s in /etc/resolv.conf.

This actually still doesn’t work and I don’t know why, nginx. Maybe I’ll figure that out today.

setting up Wireguard seems easy

I set up Wireguard for the first time and it was very straightforward!

The other side I was connecting to was already set with Wireguard, so I just needed to set up my laptop using the configuration they said to use. I just needed to:

  1. do apt-get install wireguard
  2. Download the Wireguard configuration file the other side wanted me to use and put it in /etc/wireguard/fly.conf
  3. Run wg-quick up fly
  4. done!

Day 52: testing how many Firecracker VMs I can run Day 56: A little WebAssembly