Configuring Docker Daemon Proxy Settings

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Configuring Docker Daemon for Proxy Settings

The Docker daemon can be configured to use an HTTP/HTTPS proxy for operations like pulling images or building containers from behind a corporate firewall. This is done by editing (or creating) the /etc/docker/daemon.json file. Note that this configuration applies to the daemon itself (e.g., for docker pull or docker build), not to individual containers (which would use environment variables or Docker build args).

Prerequisites

You need root or sudo access on a Linux system (this is the primary OS for Docker daemon configuration; on Windows/Mac with Docker Desktop, use the GUI settings instead).
Docker installed and running.
Know your proxy server details (e.g., http://proxy.company.com:8080 for HTTP/HTTPS proxy, and any no-proxy exceptions).

Step-by-Step Configuration

Locate or Create the Daemon Configuration File:
- Open a terminal and navigate to /etc/docker/ (create the directory if it doesn’t exist: sudo mkdir -p /etc/docker).
- Edit the file daemon.json using a text editor (e.g., sudo nano /etc/docker/daemon.json or sudo vim /etc/docker/daemon.json).
- If the file doesn’t exist, create it. Start with an empty JSON object {} if it’s new.
Add Proxy Configuration:
- Add a "proxies" section to the JSON file. Here’s a basic example:
```
{
  "proxies": {
    "http-proxy": "http://proxy.company.com:8080",
    "https-proxy": "http://proxy.company.com:8080",
    "no-proxy": "localhost,127.0.0.1,*.company.com,10.0.0.0/8"
  }
}
```
  - Explanations:
    - "http-proxy": The URL for HTTP proxy (required for non-HTTPS requests).
    - "https-proxy": The URL for HTTPS proxy (often the same as HTTP proxy).
    - "no-proxy": A comma-separated list of hosts/domains/IP ranges that should bypass the proxy (e.g., local addresses or internal domains). This prevents infinite loops.
    - If authentication is needed, use the format http://username:password@proxy.company.com:8080.
    - For SOCKS proxies, use "http-proxy": "socks5://proxy.company.com:1080".
  - If daemon.json already has existing content (e.g., other settings like "log-driver": "json-file"), merge the "proxies" section into it without duplicating keys. Ensure valid JSON syntax (use a tool like jsonlint to validate if needed).
Save and Restart the Docker Daemon:
- Save the file.
- Restart the Docker service to apply changes:
```
sudo systemctl restart docker
```
  - On older systems or non-systemd setups, use sudo service docker restart.
- Verify the daemon is running:
```
sudo systemctl status docker
```
  - Check logs if there are issues: sudo journalctl -u docker.service.
Verify the Configuration:
- Test by pulling an image (which should now route through your proxy):
```
docker pull hello-world
```
- Check if the proxy settings are applied by inspecting the daemon config:
```
docker info | grep -i proxy
```
  - You should see output like:
    HTTP Proxy: http://proxy.company.com:8080 HTTPS Proxy: http://proxy.company.com:8080 No Proxy: localhost,127.0.0.1,*.company.com,10.0.0.0/8
- If you’re using Docker in a build context, test with:
```
docker build -t test-proxy .
```
  (Assuming a simple Dockerfile that pulls a base image.)

Additional Notes

Security: Avoid hardcoding credentials in daemon.json on shared systems. Use environment variables if possible, or tools like docker config for more advanced setups.
Common Issues:
- Syntax Errors: Invalid JSON will prevent the daemon from starting. Double-check with cat /etc/docker/daemon.json and a JSON validator.
- Firewall/SELinux: Ensure your proxy is reachable and no security modules block it.
- Docker Version: This works on Docker 20.10+ (earlier versions used different env vars like HTTP_PROXY). Check your version with docker --version and upgrade if needed.
- Registry-Specific Proxies: For private registries, you might need additional config under "registry-mirrors" or insecure registries in daemon.json.
For Containers: If you need proxy settings inside running containers (not the daemon), set environment variables in the Dockerfile (e.g., ENV http_proxy=http://proxy.company.com:8080) or via docker run -e http_proxy=....
Docker Desktop (Windows/Mac): Go to Settings > Resources > Proxies, and enable/configure there—no JSON editing needed.

For more details, refer to the official Docker docs: Configure the Docker daemon. If you encounter errors, share the exact output for troubleshooting!

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