What is correct way to fix name resolution from Docker container?
I have clean Ubuntu MATE 16.04.6 LTS installed.
I installed Docker from repository here with:
sudo apt-get install docker.io
and added my user to docker
group with
sudo usermod -a -G docker $USER
then I downloaded Ubuntu 19.04 container with
docker pull ubuntu:19.04
and tried to run apt update
inside it
docker run -it ubuntu:19.04 apt update
but got network errors:
$ docker run -it ubuntu:19.04 apt update Err:1 http://archive.ubuntu.com/ubuntu disco InRelease Temporary failure resolving 'archive.ubuntu.com' Err:2 http://security.ubuntu.com/ubuntu disco-security InRelease Temporary failure resolving 'security.ubuntu.com' Err:3 http://archive.ubuntu.com/ubuntu disco-updates InRelease Temporary failure resolving 'archive.ubuntu.com' Err:4 http://archive.ubuntu.com/ubuntu disco-backports InRelease Temporary failure resolving 'archive.ubuntu.com' Reading package lists... Done Building dependency tree Reading state information... Done All packages are up to date. W: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/disco/InRelease Temporary failure resolving 'archive.ubuntu.com' W: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/disco-updates/InRelease Temporary failure resolving 'archive.ubuntu.com' W: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/disco-backports/InRelease Temporary failure resolving 'archive.ubuntu.com' W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/disco-security/InRelease Temporary failure resolving 'security.ubuntu.com' W: Some index files failed to download. They have been ignored, or old ones used instead.
The /etc/resolv.conf
inside container is the following:
$ docker run -it ubuntu:19.04 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 nameserver 8.8.8.8 nameserver 8.8.4.4
The host system has internet, the NetworkManager is used with default settings:
$ cat /etc/NetworkManager/NetworkManager.conf [main] plugins=ifupdown,keyfile,ofono dns=dnsmasq [ifupdown] managed=false
all files on the system are unchanged - the debsums --changed --all --silent
command returns nothing.
The requested output of iptables -S
is below:
$ sudo iptables -S
-P INPUT ACCEPT
-P FORWARD DROP
-P OUTPUT ACCEPT
-N DOCKER
-N DOCKER-ISOLATION-STAGE-1
-N DOCKER-ISOLATION-STAGE-2
-N DOCKER-USER
-A FORWARD -j DOCKER-USER
-A FORWARD -j DOCKER-ISOLATION-STAGE-1
-A FORWARD -o docker0 -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
-A FORWARD -o docker0 -j DOCKER
-A FORWARD -i docker0 ! -o docker0 -j ACCEPT
-A FORWARD -i docker0 -o docker0 -j ACCEPT
-A DOCKER-ISOLATION-STAGE-1 -i docker0 ! -o docker0 -j DOCKER-ISOLATION-STAGE-2
-A DOCKER-ISOLATION-STAGE-1 -j RETURN
-A DOCKER-ISOLATION-STAGE-2 -o docker0 -j DROP
-A DOCKER-ISOLATION-STAGE-2 -j RETURN
-A DOCKER-USER -j RETURN
Which settings should I change to fix DNS (name resolution) from Docker container?
Notes:
- I know about disabling DNS masquerading (
#dns=dnsmasq
), but I do not want to use this option. - I got the same result while using Docker-CE from docker.com.
- The system installed from netinstall mini.iso does not suffer from aforementioned problem. It uses
ifupdown
. So the NetworkManager is the root of this problem.
The solution for docker run
is very simple - we need to choose host network with --network host
option:
docker run -it --network host ubuntu:19.04 apt update
and then the problem will be solved.
But it also should be noted that docker build
has --network
option only starting only from 18.04 LTS. So if we need docker build --network host
for 16.04 LTS we need to use docker-ce
package from docker.com.