When running applications in Docker containers, it’s common to need access to services running on the host machine, such as a local database, API, or development server. But by default, localhost inside a Docker container refers to the container itself, not the host.
So, how can you connect to the host’s localhost from inside a Docker container? Let’s explore the most effective solutions based on your operating system and Docker setup.
🧠 Understanding the Problem
- Inside a container,
localhost(127.0.0.1) refers to the container’s own loopback interface. - If your host is running a service on
localhost:5000, a container cannot access it vialocalhost:5000. - Instead, the container needs a way to reach the host network.
✅ Solution 1: Use host.docker.internal (Docker for Windows & Mac)
If you are using Docker Desktop on Windows or macOS, Docker provides a special DNS name: host.docker.internal.
How to Use:
curl http://host.docker.internal:5000
Or in a Dockerfile or script inside the container:
ping host.docker.internal
🛠 Supported on:
- Docker Desktop for Windows
- Docker Desktop for Mac
💡 Tip: This does not work natively on Linux, unless explicitly configured.
✅ Solution 2: Linux – Use --network="host" Mode
On Linux, the easiest way to access the host’s localhost is to run the container in host network mode:
docker run --network="host" your-image
This makes the container share the host’s network stack, so localhost inside the container is the same as localhost on the host.
⚠️ Note:
- Only works on Linux.
- Not compatible with Docker Desktop for Windows/Mac.
- Can pose security concerns as there’s no network isolation.
✅ Solution 3: Find Host IP from Inside the Container
You can connect to the host machine’s IP address on the Docker bridge network. The default gateway of the container is often the host machine’s bridge IP.
Step-by-Step:
- Run this inside your container:
ip route | grep default - Output might look like:
default via 172.17.0.1 dev eth0 - Then, connect to the host using that IP:
curl http://172.17.0.1:5000
🔄 Alternative:
You can also hardcode the host IP (e.g., 172.17.0.1), but this can vary by system and network setup.
✅ Solution 4: Use Docker Compose with Extra Host Mapping
If you’re using Docker Compose, you can manually map a hostname to the host machine:
services:
app:
image: your-app
extra_hosts:
- "host.docker.internal:host-gateway"
🛠 Requires:
- Docker v20.10.0+ (for
host-gatewaysupport on Linux)
Now your container can access the host using:
curl http://host.docker.internal:5000
🧪 Example Use Case: Accessing a Database on Host
If your host machine runs a local PostgreSQL database on port 5432, and you want to access it from a container:
On Windows/Mac:
psql -h host.docker.internal -p 5432 -U postgres
On Linux (with host networking):
docker run --network host postgres psql -h 127.0.0.1 -U postgres
✅ Summary
| Method | OS / Platform | Use Case |
|---|---|---|
host.docker.internal | Windows / macOS | Most common & simple method |
--network="host" | Linux only | Full access to host network |
Use 172.17.0.1 | Linux (Docker bridge) | When bridge IP is known |
extra_hosts with Compose | Linux + Docker 20.10+ | Flexible and Docker-native |
🚀 Final Tip
Always make sure your host firewall or services (e.g., MySQL, PostgreSQL) are listening on 0.0.0.0 or specific interfaces, not just 127.0.0.1. Otherwise, the container won’t be able to reach them even if the address is correct.