Why does my Docker container have internet access, but devices on my local network can't reach the service?

[hackerXcult]

I'm running a Python web application inside a Docker container on Ubuntu.

The application starts correctly and the container can access the internet without any issues. I can also see the service running when I check processes inside the container.

The confusing part is that other devices on my local network cannot reach the application even though the host machine itself can access it.

I verified:

• The container is running
• The application is listening on the expected port
• Ubuntu firewall is disabled
• Docker port mapping appears correct

One thing I noticed is that the application is bound to 127.0.0.1 inside the container.

Can binding to localhost inside a container prevent external access even when the port is published with Docker?

I'm trying to understand whether this is a Docker networking issue or an application configuration issue.

[vignesh0x]

Yes, binding to 127.0.0.1 inside the container is often the cause.

When an application listens on 127.0.0.1, it only accepts connections originating from inside that container.

Docker can publish the port correctly, but if the application itself is not listening on all interfaces, incoming traffic will never reach it.

For services that should be accessible outside the container, bind to:

0.0.0.0

instead of:

127.0.0.1

For example:

app.run(host="0.0.0.0", port=5000)

or

python -m http.server --bind 0.0.0.0

A quick way to verify is to enter the container and check which address the process is listening on.

This issue is common because applications often work perfectly when tested locally, which makes Docker networking look like the problem even though the real issue is the bind address.