When working with Docker containers, you may sometimes need a container to access a service running on the host machine—like a database, API server, or custom service on a specific port. This is a common scenario during development, testing, or local integration.
In this post, you’ll learn:
- How networking works between containers and hosts
- How to access a host port from within a container
- Solutions for different operating systems
🧠 Understanding the Problem
By default, Docker containers run in isolated networks and cannot directly access localhost (or 127.0.0.1) of the host machine.
For example, if your host is running a web server on localhost:8000, running this inside a container won’t work:
curl http://localhost:8000
Why? Because localhost in the container refers to the container itself—not your host.
✅ Solution 1: Use host.docker.internal (Linux, macOS, Windows)
Docker provides a special DNS name:
host.docker.internal
This resolves to the internal IP address of the host, allowing containers to reach services running on the host system.
🔧 Example
curl http://host.docker.internal:8000
Use this inside your container to access the host’s service running on port 8000.
📌 Notes:
- macOS and Windows support this natively.
- For Linux, it works with Docker Desktop, but may require additional setup if you’re using Docker Engine.
🔁 Linux Alternative (Non-Docker-Desktop)
On Linux systems without Docker Desktop, host.docker.internal may not resolve. Instead, use the host’s IP address from the container’s perspective.
Step-by-step:
- Get the IP of the host network interface (typically
eth0orwlo1):
ip addr show
- Use the IP address directly in the container:
curl http://192.168.x.x:8000
Or pass it as an environment variable when running the container:
docker run -e HOST_IP=192.168.x.x myimage
🔧 Solution 2: Use Docker’s Host Network (Linux Only)
You can run the container using the host’s network stack:
docker run --network host myimage
Now, inside the container, localhost refers to the host’s network.
⚠️ Works only on Linux, not supported on Docker Desktop for Windows/macOS.
📦 Bonus: Define the Host in /etc/hosts
You can manually add a custom alias to the host machine in your container’s /etc/hosts:
docker run --add-host=myhost:192.168.x.x myimage
Then, in your app:
curl http://myhost:8000
📝 Summary
| Method | OS Compatibility | Notes |
|---|---|---|
host.docker.internal | Windows/macOS/Linux* | Easiest way with Docker Desktop |
| Use host IP address | All | Requires knowing the IP |
--network host | Linux only | Shares full network with host |
--add-host=myhost:<IP> | All | Creates a custom alias |
✅ Conclusion
Accessing host ports from Docker containers is simple once you understand the networking model. Use host.docker.internal for cross-platform ease, or switch to --network host or IP-based approaches on Linux.
Proper configuration ensures your containers can seamlessly integrate with local services—great for development and testing workflows.