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How to configure Docker DNS on Ubuntu in a corporate environment?

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When you are in a corporate environment, network is often configured to restrict outgoing requests, such as DNS resolution requests. By default, Docker uses Google DNS (8.8.8.8 and 8.8.4.4) to resolve domain names:

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$ docker run busybox nslookup google.com
Server:    8.8.8.8
Address 1: 8.8.8.8
nslookup: can't resolve 'google.com'

If you are in a corporate environment, resolution fails because you have to use your internal DNS server.

You can find many, many documentation about how to configure Docker DNS on Ubuntu (such as official Docker doc), but none of them answer these requirements all together:

1/ Configuration must be portable: works at home or at work or anywhere else

2/ Configuration must be written in files not provided by a deb package to avoid conflicts after package updates

Portable configuration

Ubuntu provides Dnsmasq, a local DNS server configured to use DNS server of your network through DHCP. Docker can’t use it because it doesn’t allow to use a local DNS server if its IP address is a local configuration, such as 127.0.0.1.

So we’ll configure Dnsmasq to listen to another available IP address, such as the one provided by docker0 interface, to solve this issue.

Edit the new file /etc/NetworkManager/dnsmasq.d/docker.conf (as sudo):

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interface=docker0

Then restart NetworkManager service:

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sudo service network-manager restart

Configure Docker DNS

Extract the IP address of the docker0 interface:

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$ docker network inspect bridge | grep Gateway
                    "Gateway": "172.17.0.1"

Then edit /etc/docker/daemon.json (as sudo):

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{
    "dns": ["172.17.0.1"]
}

Restart Docker:

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sudo service docker restart

Finally, check DNS resolution works again:

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$ docker run busybox nslookup google.com
Server:    172.17.0.1
Address 1: 172.17.0.1
Name:      google.com
Address 1: 2a00:1450:4009:811::200e lhr26s02-in-x200e.1e100.net
Address 2: 216.58.198.174 lhr25s10-in-f14.1e100.net

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