Configuring Docker to Work Behind a Proxy Server

Docker is a popular containerization platform that allows developers to package, ship, and run applications in containers. However, when working behind a proxy server, Docker may not be able to download images or access external resources. In this tutorial, we will explore how to configure Docker to work behind a proxy server.

Understanding Proxy Servers

A proxy server acts as an intermediary between a client and a server, forwarding requests and responses between the two. When working behind a proxy server, it’s essential to configure your tools and applications to use the proxy server to access external resources.

Configuring Docker to Use a Proxy Server

To configure Docker to use a proxy server, you need to set environment variables that specify the proxy server’s URL and port. The HTTP_PROXY and HTTPS_PROXY environment variables are used to specify the proxy server for HTTP and HTTPS requests, respectively.

On Linux systems, you can create a systemd drop-in directory for the Docker service and add a file that sets the HTTP_PROXY and HTTPS_PROXY environment variables. For example:

mkdir /etc/systemd/system/docker.service.d

Create a file called /etc/systemd/system/docker.service.d/http-proxy.conf with the following contents:

[Service]
Environment="HTTP_PROXY=http://proxy.example.com:80/"
Environment="HTTPS_PROXY=http://proxy.example.com:80/"

If you have internal Docker registries that you need to contact without proxying, you can specify them via the NO_PROXY environment variable:

Environment="HTTP_PROXY=http://proxy.example.com:80/"
Environment="HTTPS_PROXY=http://proxy.example.com:80/"
Environment="NO_PROXY=localhost,127.0.0.0/8,docker-registry.somecorporation.com"

After creating the file, reload the systemd daemon and restart the Docker service:

sudo systemctl daemon-reload
sudo systemctl restart docker

On other Linux distributions, such as CentOS, you can add the following lines to the /etc/sysconfig/docker file:

HTTP_PROXY="http://<proxy_host>:<proxy_port>"
HTTPS_PROXY="http://<proxy_host>:<proxy_port>"

Replace <proxy_host> and <proxy_port> with your proxy server’s hostname and port.

Verifying the Configuration

To verify that Docker is using the proxy server, you can use the docker command to pull an image:

sudo docker pull busybox

If the configuration is correct, Docker should be able to download the image without any issues.

Configuring Docker on Mac or Windows

If you’re using Docker for Mac or Docker for Windows, you can configure the proxy settings through the Docker tray icon. Right-click the icon and select Preferences (Windows: Settings), then go to Advanced, and under Proxies specify your proxy settings. Click Apply and Restart and wait until Docker restarts.

Best Practices

When configuring Docker to work behind a proxy server, keep in mind the following best practices:

• Use the HTTP_PROXY and HTTPS_PROXY environment variables to specify the proxy server’s URL and port.
• Specify internal Docker registries that you need to contact without proxying via the NO_PROXY environment variable.
• Verify the configuration by pulling an image or accessing external resources.

By following these steps and best practices, you should be able to configure Docker to work behind a proxy server and access external resources without any issues.