sdns 📂

A DNS server based on minimal static configuration

Use cases

Make a domain always resolve to localhost

sudo sdns \
        --port 53 \
        --addr 127.0.0.11 \
        'domain=test.cirocosta.io,ip=192.168.0.103,ns=mynameserver.com' \
        'domain=*.cirocosta.io,ip=127.0.0.1,ip=10.0.0.10'

Retrieve information about each DNS request being performed

sudo sdns \
        --debug \               # logs the requests to 'stderr'
        --port 53 \             
        --addr 127.0.0.11 \
        --recursor 8.8.8.8

Install

Pick the latest version in the project’s releases page and then “untar” the binary to the desired location in $PATH.

For instance:

URL=https://github.com/cirocosta/sdns/releases/download/v0.0.1/sdns_0.0.1_darwin_amd64.tar.gz
mkdir -p /tmp/sdns
curl -o /tmp/sdns/sdns.tar.gz -L $URL
tar xzfv /tmp/sdns/sdns.tar.gz -C /tmp/sdns
sudo mv /tmp/sdns/sdns /usr/local/bin/sdns

Note.: you can also use go to install it: go get -u github.com/cirocosta/sdns. Just make sure that you can run the binary with the necessary privileges to bind to port 53.

Docker

Using sdns in a Docker container is completely fine, you can find the image under cirocosta/sdns.

docker run -d \
        --network host \        # use the host network stack (not required)
        cirocosta/sdns \        # use the image
        --debug \               # logs the requests to 'stderr'
        --port 53 \             
        --addr 127.0.0.11 \
        --recursor 8.8.8.8

Usage

Usage: sdns [--port PORT] [--address ADDRESS] [--debug] [--recursor RECURSOR] [DOMAINS [DOMAINS ...]]
Positional arguments:
  DOMAINS                list of domains
Options:
  --port PORT, -p PORT   port to listen to [default: 1053]
  --address ADDRESS, -a ADDRESS
                         address to bind to
  --debug, -d            turn debug mode on [default: true]
  --recursor RECURSOR, -r RECURSOR
                         list of recursors to honor [default: [8.8.8.8 8.8.4.4]]
  --help, -h             display this help and exit

Running as the system’s DNS

Ubuntu 17.04

If you’re on Ubuntu 17.04 you might have noticed that systemd places a DNS resolver at 127.0.0.53:

cat /etc/resolv.conf
# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
#     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
# 127.0.0.53 is the systemd-resolved stub resolver.
# run "systemd-resolve --status" to see details about the actual nameservers.
127.0.0.53

As systemd-resolve is a systemd service like any other, we just need to stop the unit and then place sdns at 127.0.0.53 listening on the default DNS service port (53):

sudo systemctl stop systemd-resolved
sudo sdns \                             # run as sudo to be able to bind to 53
        --debug \                       # with --debug we capture more logs
        --address 127.0.0.53 \          # listen on the expected IP
        --port 53                       # on port 53
# Now if you stop 'sdns' you'll lose DNS resolving.
# To get systemd-resolve in place again just
# issue `sudo systemctl start systemd-resolved`.

Now you can head to your web browser and see the queries coming to SDNS.

If you wish you can also run sdns as a systemd service (like systemd-resolved)