I have a Rails application that I want to deploy using Docker on an Ubuntu server. I have the Dockerfile for the application already set up, right now I want to view the nginx conf in its container.

I ran the command below to start an nginx container in an interactive mode:

docker run -i -t nginx:latest /bin/bash

Right now I am trying to install nano editor in order to view the configuration for nginx configuration (nginx.conf) using the commands below:

apt-get update
apt-get install nano
export TERM=xterm

However, when I run the first command apt-get update, I get the error below:

Err:1 http://security.debian.org/debian-security buster/updates InRelease
  Temporary failure resolving 'security.debian.org'
Err:2 http://deb.debian.org/debian buster InRelease                  
  Temporary failure resolving 'deb.debian.org'
Err:3 http://deb.debian.org/debian buster-updates InRelease
  Temporary failure resolving 'deb.debian.org'
Reading package lists... Done    
W: Failed to fetch http://deb.debian.org/debian/dists/buster/InRelease  Temporary failure resolving 'deb.debian.org'
W: Failed to fetch http://security.debian.org/debian-security/dists/buster/updates/InRelease  Temporary failure resolving 'security.debian.org'
W: Failed to fetch http://deb.debian.org/debian/dists/buster-updates/InRelease  Temporary failure resolving 'deb.debian.org'
W: Some index files failed to download. They have been ignored, or old ones used instead.

I have checked very well it has nothing to do with network connectivity. I would need some help. Thank you.

Here's how I solved it:

Start the docker container for the application in an interactive mode, in my case it an nginx container :

docker run -i -t nginx:latest /bin/bash

Run the command below to grant read permission to the others role for the resolv.conf file:

chmod o+r /etc/resolv.conf

Note: If you are having this issue on your host machine (Ubuntu Linux OS) and not for the Docker containers, then run the same command adding sudo to it in the host machine terminal:

sudo chmod o+r /etc/resolv.conf

Endeavour to exit your bash interactive terminal once you run this:

exit

And then open a new bash interactive terminal and run the commands again:

apt-get update
apt-get install nano
export TERM=xterm

Everything should work fine now.

Reference to this on Digital Ocean: Apt error: Temporary failure resolving 'deb.debian.org'

That's all.