Master Docker Proxy Setup: Daemon, Container, and Build Configurations

Sometimes network constraints such as corporate NAT require using a proxy. Docker proxy configuration can be complex because it involves three scenarios, but all rely on Linux environment variables like http_proxy.

dockerd proxy

When running docker pull, the daemon dockerd performs the operation, so the proxy must be set in the daemon's environment, which is managed by systemd. Create a drop‑in directory and a proxy configuration file:

sudo mkdir -p /etc/systemd/system/docker.service.d
touch /etc/systemd/system/docker.service.d/proxy.conf

In proxy.conf add:

[Service]
Environment="HTTP_PROXY=http://proxy.example.com:8080/"
Environment="HTTPS_PROXY=http://proxy.example.com:8080/"
Environment="NO_PROXY=localhost,127.0.0.1,.example.com"

Replace proxy.example.com:8080 with a reachable, authentication‑free proxy (often set up locally with cntlm).

Container proxy

For containers that need internet access, configure ~/.docker/config.json. The following JSON works for Docker 17.07+:

{
  "proxies": {
    "default": {
      "httpProxy": "http://proxy.example.com:8080",
      "httpsProxy": "http://proxy.example.com:8080",
      "noProxy": "localhost,127.0.0.1,.example.com"
    }
  }
}

This user‑level configuration is convenient for personal development environments. In CI/CD pipelines or production, injecting proxy variables with -e is often preferable to avoid dependency on the host configuration.

docker build proxy

Although docker build also runs a container, it does not inherit the user‑level proxy settings. Pass proxy arguments explicitly:

docker build . \
  --build-arg "HTTP_PROXY=http://proxy.example.com:8080/" \
  --build-arg "HTTPS_PROXY=http://proxy.example.com:8080/" \
  --build-arg "NO_PROXY=localhost,127.0.0.1,.example.com" \
  -t your/image:tag

Both docker run and docker build operate in isolated networks; a proxy bound to localhost:3128 will not work unless --network host is used. Typically you need an external proxy IP and the proxy must run in gateway mode.