Having troubles with Docker DNS?

Configure_Docker_DNS.sh

# First, verify that your Docker DNS are actually incorrecly configured
# by dowloading the Debian image, creating a container and ping the Debian archives repository from it.

# $ docker run -it debian ping 128.31.0.62 # the IP of the repository
# This should work:
# > [...] 2 packets transmitted, 2 packets received, 0% packet loss
# If not, this is not a DNS issue.

# $ docker run -it debian ping deb.debian.org # the URL of the repository
# If you get this message:
# > ping: unknown host
# you may have a DNS issue and must execute this script.

# 1. Get your DNS
dns=($(nmcli device show $(ip route list | awk '/^default/ {print $5}') | grep DNS | sed -E "s/.*:\s+//g"))

# 2. Set configure Docker DNS (the way to do it depends if your init system is systemd or not)
if ps -o comm -1 | grep -q systemd; then
  cat /lib/systemd/system/docker.service | sed '/^ExecStart.*/ s/$/ --dns='"${dns[1]}"' --dns='"${dns[2]}"'/' > /tmp/docker.service
  sudo mv /tmp/docker.service /lib/systemd/system/docker.service
elif
  sudo bash -c "echo 'DOCKER_OPTS=\"--dns '${dns[1]}' --dns '${dns[2]}'\"' >> /etc/default/docker" 
fi

# Now check again!
# $ docker run -it debian ping deb.debian.org
# > [...] 2 packets transmitted, 2 packets received, 0% packet loss
# Hurrah!