felixhummel / devdns

capture and modify a complete domain locally with NetworkManager, dnsmasq and CoreDNS

Motivation

To test www.example.org behind ELB, the development system should see a CNAME record pointing from www.example.org to www-123456789.eu-central-1.elb.amazonaws.com..

Unfortunately, dnsmasq on can only handle CNAME records for its own domain ¹. But it can delegate a whole zone.

CoreDNS to the rescue!

Assumptions / Prerequisites

• NetworkManager on 127.0.0.1 contains dnsmasq, that can be configured via /etc/NetworkManager/dnsmasq.d/ (for Ubuntu 18.04: see below).
• Docker and Docker Compose (see NOTES.md) for manual installation

CoreDNS

Run CoreDNS

docker-compose up -d

and validate that

dig +short @127.0.0.1 -p 1053 example.org
dig +short @127.0.0.1 -p 1053 foo.example.org

both return 127.0.0.1 as specified in zones/example.org.

NetworkManager

Make NetworkManager use CoreDNS for example.org:

cat <<'EOF' | sudo tee -a /etc/NetworkManager/dnsmasq.d/example.org.conf
# this is coredns
server=/example.org/127.0.0.1#1053
EOF

sudo service NetworkManager reload

# to debug:
# journalctl -fu NetworkManager

Validate:

dig +short example.org
dig +short foo.example.org

should return the same lines as above.

Validate in browser (restart it first!):

python -mhttp.server 9876

• http://example.org:9876/
• http://foo.example.org:9876/

Ubuntu 18.04

Disable resolved's stub resolver:

sudo -i
systemd --version  # >= 232 (https://unix.stackexchange.com/a/358485/120440)
echo 'DNSStubListener=no' >> /etc/systemd/resolved.conf
systemctl restart systemd-resolved

Enable dnsmasq in NetworkManager putting dns=dnsmasq into /etc/NetworkManager/NetworkManager.conf, e.g.:

# /etc/NetworkManager/NetworkManager.conf
[main]
dns=dnsmasq

And restart NetworkManager:

systemctl restart NetworkManager

Footnotes

1. https://github.com/imp/dnsmasq/blob/master/dnsmasq.conf.example#L646 ↩