Securing Microservices with Railway Private Networking

The Public Endpoint Problem

When deploying a microservices architecture, a common mistake is exposing every internal API to the public internet just to make them reachable by other services. This increases your attack surface, forces you to manage complex API keys for internal traffic, and introduces unnecessary latency as requests leave and re-enter the cloud provider’s gateway.

The solution is to move inter‑service communication to a private layer. Railway provides an internal networking system that allows services within the same project to communicate via private DNS names, bypassing the public internet entirely.

How Private Networking Operates

Railway assigns each service a private hostname based on its service name. These hostnames resolve to internal IP addresses that are only routable within the project’s environment. Because this traffic never hits the public gateway, it is inherently shielded from external scans and DDoS attacks.

This system uses standard TCP/UDP traffic. Whether you are connecting a Node.js backend to a Redis cache or a Python worker to a Go API, you use the same HTTP clients or database drivers you would use for any other network request.

Configuring Your Services for Internal Access

For private networking to function, your application must be configured to listen on the correct network interface. A frequent point of failure is binding the application to 127.0.0.1 (localhost).

Since the internal network request arrives from a different container, the application must listen on 0.0.0.0. This tells the application to accept traffic from any network interface, including the one Railway uses for internal service discovery.

Worked Example: Connecting a Backend to a Private API

Imagine a project with two services: api-gateway and user-service. You want the gateway to fetch user data without exposing the user-service to the web.

1. Service Setup: In the Railway dashboard, ensure the user-service does not have a public domain assigned in the Networking tab.
2. Internal Address: Identify the internal hostname. By default, this follows the pattern service-name.railway.internal. In this case: user-service.railway.internal.
3. Environment Variable: In the api-gateway service settings, add an environment variable: USER_SERVICE_URL=http://user-service.railway.internal:8080 (replace 8080 with the actual port the service uses).

Verification: To test the connection, you can use the Railway CLI or a temporary shell into the api-gateway container and run:

# Run this from the api-gateway terminal
curl -I http://user-service.railway.internal:8080/health

If the service is configured correctly, you will receive a response. If you attempt to visit user-service.railway.internal from your local browser, the request will fail because the DNS is only resolvable inside the Railway environment.

Trade‑offs and Limitations

• Project Isolation: Internal DNS only works for services within the same project environment. You cannot use .railway.internal addresses to connect to services in a different Railway project.
• Authorization: Private networking provides network‑level isolation, not application‑level authorization. If a service in your project is compromised, it can reach any other private service. You should still implement basic authentication or JWT validation for sensitive internal endpoints.
• Debugging: Since these services are not public, you cannot test them using tools like Postman or Insomnia from your local machine. You must rely on logs or a “jump box” service within the project to diagnose connectivity issues.

Closing Action

Audit your current Railway project. If you have internal services with public URLs that are only used by other services, remove those public domains and switch to .railway.internal hostnames. This immediately reduces your public footprint and improves internal request latency.