Configure Docker Daemon DNS Servers

Configure Docker Daemon DNS Servers | Generated by AI

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To configure DNS servers for the Docker daemon (which will be used by containers unless overridden at the container level), you can edit the /etc/docker/daemon.json file. This file allows you to customize Docker’s runtime behavior.

Steps to Configure DNS

Edit the daemon.json file:
- If the file doesn’t exist, create it with root privileges (e.g., using sudo nano /etc/docker/daemon.json or your preferred editor).
- Add or update the dns key as an array of IP addresses for the DNS servers. For example, to use Google’s public DNS (8.8.8.8 and 8.8.4.4):
```
{
  "dns": ["8.8.8.8", "8.8.4.4"]
}
```
  - You can add more servers if needed (e.g., Cloudflare’s 1.1.1.1).
  - This setting applies to all containers created with the default network unless specified otherwise.
Validate the JSON:
- Ensure the file is valid JSON. You can use a tool like jq to check: jq . /etc/docker/daemon.json. If it errors, fix the syntax.
Restart the Docker service:
- Apply the changes by restarting Docker:
```
sudo systemctl restart docker
```
  - On non-systemd systems (e.g., older Linux distros), use sudo service docker restart.
- Verify the status: sudo systemctl status docker.
Test the configuration:
- Run a test container and check its DNS resolution:
```
docker run --rm busybox nslookup google.com
```
  - It should resolve using your configured DNS servers.

Notes

Scope: This configures DNS for the Docker daemon on the host, affecting outbound name resolution for containers. It doesn’t change the host’s system DNS.
Overrides: If a container needs different DNS (e.g., via --dns flag in docker run), it will override this daemon-level setting.
Security: Using public DNS like 8.8.8.8 is fine for most cases, but consider internal DNS for enterprise environments.
Documentation: For more options (e.g., DNS search domains), see the official Docker docs on daemon.json.

If you encounter errors (e.g., permission issues or JSON parsing), share the details for further troubleshooting.

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