Docker configures DNS

Docker doesn't customize the image specifically for each container, so how do you customize the host name and DNS configuration of the configuration container? The secret is that it uses virtual files to mount the three related profiles of the incoming container.

The mount information can be seen in the container using the mount command:

$ mount
...
/dev/disk/by-uuid/1fec...ebdf on /etc/hostname type ext4 ...
/dev/disk/by-uuid/1fec...ebdf on /etc/hosts type ext4 ...
tmpfs on /etc/resolv.conf type tmpfs ...
...

This mechanism allows the dns configuration of all Docker containers to be updated immediately through /etc/resolv.conf as soon as the host host DNS information is updated.

If the user wants to manually specify the configuration of the container, they can take advantage of the following options.

-h HOSTNAME or --hostname=HOSTNAME host name of the container, which is /etc/hostname /etc/hosts However, it is not visible outside the docker ps nor in /etc/hosts

--link=CONTAINER_NAME:ALIAS host name of a different container /etc/hosts container to connect to it using the host name ALIAS.

--dns=IP_ADDRESS a DNS server /etc/resolv.conf which the container uses to resolve /etc/hosts

--dns-search=DOMAIN domain for the container, and when the .example.com DNS searches not only for hosts, but also host.example.com Note: Without the last 2 options above, Docker will configure the /etc/resolv.conf on the host.