Can't install pip packages inside a docker container with Ubuntu

Question

I'm following the fig guide to using docker with a python application, but when docker gets up to the command

RUN pip install -r requirements.txt 

I get the following error message:

Step 3 : RUN pip install -r requirements.txt  ---> Running in fe0b84217ad1 Collecting blinker==1.3 (from -r requirements.txt (line 1))   Retrying (Retry(total=4, connect=None, read=None, redirect=None)) after connection broken by 'ProtocolError('Connection aborted.', gaierror(-2, 'Name or service not known'))': /simple/blinker/ 

This repeats several times and then I get another message:

Could not find any downloads that satisfy the requirement blinker==1.3 (from -r requirements.txt (line 1))   No distributions at all found for blinker==1.3 (from -r requirements.txt (line 1)) 

So for some reason pip can't access any packages from inside a docker container. Is there anything I need to do to allow it internet access?

However pip works fine to install things outside of the docker container, and worked fine even with that exact package (blinker==1.3) so that's not the problem. Also this problem isn't specific to that package. I get the same issue with any pip install command for any package.

Does anyone have any idea what's going on here?

Answer 1

Your problem comes from the fact that Docker is not using the proper DNS server. You can fix it in three different ways :

1. Adding Google DNS to your local config

Modifying /etc/resolv.conf and adding the following lines at the end

# Google IPv4 nameservers nameserver 8.8.8.8 nameserver 8.8.4.4

If you want to add other DNS servers, have a look here.

However this change won't be permanent (see this thread). To make it permanent : $ sudo nano /etc/dhcp/dhclient.conf Uncomment and edit the line with prepend domain-name-server : prepend domain-name-servers 8.8.8.8, 8.8.4.4;

Restart dhclient : $ sudo dhclient.

2. Modifying Docker config

As explained in the docs :

Systems that run Ubuntu or an Ubuntu derivative on the desktop typically use 127.0.0.1 as the default nameserver in /etc/resolv.conf file.

To specify a DNS server for use by Docker :

1. Log into Ubuntu as a user with sudo privileges.  2. Open the /etc/default/docker file for editing :      $ sudo nano /etc/default/docker  3. Add the following setting for Docker.      DOCKER_OPTS="--dns 8.8.8.8"  4. Save and close the file.  5. Restart the Docker daemon :      $ sudo systemctl restart docker 

3. Using a parameter when you run Docker

When you run docker, simply add the following parameter : --dns 8.8.8.8

Answer 2

I needed to add --network=host to my docker build command:

docker build --network=host -t image_name .