DockerHow-ToBeginner · 4 min read

How to Use DNS in Docker: Simple Guide with Examples

To use DNS in Docker, you can specify custom DNS servers with the --dns option in docker run or set DNS in Docker Compose files under dns. This lets containers resolve domain names using your chosen DNS servers instead of the default Docker DNS.

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Syntax

The main way to set DNS in Docker is using the --dns flag when running a container. You provide one or more DNS server IP addresses that the container will use for name resolution.

Example parts:

docker run: command to start a container
--dns <IP>: sets a DNS server IP for the container
image_name: the Docker image to run

bash

docker run --dns 8.8.8.8 --dns 8.8.4.4 image_name

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Example

This example runs an alpine container with Google's public DNS servers set. It then uses nslookup to resolve example.com.

bash

docker run --rm --dns 8.8.8.8 alpine sh -c "apk add --no-cache bind-tools && nslookup example.com"

Output

Server: 8.8.8.8 Address 1: 8.8.8.8 google-public-dns-a.google.com Non-authoritative answer: Name: example.com Address: 93.184.216.34

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Common Pitfalls

Common mistakes when using DNS in Docker include:

Not specifying DNS servers when the default Docker DNS is blocked or unreachable.
Using invalid IP addresses for DNS servers.
Forgetting to add the --dns flag or the dns key in Docker Compose.
Overriding DNS but not restarting containers, so changes don't apply.

Example of wrong and right usage:

bash

# Wrong: no DNS specified, might fail if default DNS is unreachable

docker run alpine nslookup example.com

# Right: specify DNS servers explicitly

docker run --dns 8.8.8.8 alpine nslookup example.com

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Quick Reference

Option	Description	Example
--dns	Set custom DNS server for container	docker run --dns 8.8.8.8 alpine
dns (Compose)	Set DNS servers in docker-compose.yml	dns: - 8.8.8.8 - 8.8.4.4
--dns-search	Set DNS search domain	docker run --dns-search example.com alpine
--dns-opt	Set DNS options	docker run --dns-opt ndots:2 alpine

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Key Takeaways

Use the --dns flag to specify custom DNS servers when running Docker containers.

You can also set DNS servers in docker-compose.yml under the dns key for multi-container setups.

Always verify DNS server IPs are correct and reachable from your Docker host.

Restart containers after changing DNS settings to apply the new configuration.

Use tools like nslookup inside containers to test DNS resolution.