Very basic DNS server that resolves AWS's EC2 internal FQDNs (ex: ip-192-0-2-1.us-west-2.compute.internal) by extracting the IP out of the hostname.

Includes an optional subcommand that sets up macOS to automatically direct all "*.internal" queries to this daemon.

• Go 1.13 or later to build.

NOTE: Only macOS is currently supported.

1. Run: brew install brandt/personal/awsresolver
2. Run: sudo awsresolver setup (installs /etc/resolver/internal)
3. Run: brew services start awsresolver

This hooks into macOS's resolver. That means things like ping and ssh will do what you expect, but dig will not.

To confirm it's working, run: ping ip-192-0-2-1.us-west-2.compute.internal

If awsresolver is correctly setup, you will see ping attempt to reach 192.0.2.1:

# SUCCESS                                     vvvvvvvvv
PING ip-192-0-2-1.us-west-2.compute.internal (192.0.2.1): 56 data bytes
Request timeout for icmp_seq 0
Request timeout for icmp_seq 1

This tool listens for A record requests ending in .internal, extracts the IP from the requested name, and returns it as a response. It binds to UDP and TCP 127.0.0.1:1053.

Mac OS X has a cool feature that allows you to configure different resolvers by domain. (See: man 5 resolver) When you run sudo awsresolver setup, it writes a config file to /etc/resolver/internal that steers *.internal requests to 127.0.0.1:1053.

Note that the resolver(5) config only applies to DNS resolution performed through the built-in OS facilities. So ping, ssh, and Chrome will be routed to this resolver, but by default dig will not.

To query with dig, point it directly at the resolver like so: dig @127.0.0.1 -p 1053 ip-192-0-2-1.us-west-2.compute.internal

To build from source, simply run these commands from inside this repo:

go mod vendor # optional
make

The compiled binary is here: bin/awsresolver

To uninstall:

1. Run: sudo rm -f /etc/resolver/internal
2. Run: brew uninstall awsresolver

• J. Brandt Buckley