How to tunnel localhost to the public Internet

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Introduction

In this article, I’m going to show you how you can tunnel your localhost environment to a public Internet address that can be accessed by other services you are using for testing.

Why tunnel localhost to a public Internet address?

If you are optimizing the front-end of a given web application and want to see how effective your changes are, you can use a tool like GT Metrix or Pingdom Website Testing.

The problem is that those tools can access only a public Internet address, not your localhost environment. And, while you can deploy your temporary changes to a QA environment that’s publicly accessible, there’s a much simpler way to achieve this goal.

Or, while developing RevoGain, the most awesome Revolut trading grain calculator, I had to test the FastSpring payment integration. The payment callbacks need a public Internet address that FastSpring calls after making a purchase. To test the integration, you’d need to expose your localhost environment to a public Internet address so that FastSpring can call your own environment.

And, the solution to this problem is to open a networking tunnel between localhost and some public Internet address all those services can access.

Networking tunnel

In networking, a tunnel allows you to transport packets from a private network to a public network. For instance, tunneling is used with VPN (virtual private networks) to secure network connections.

The Linux ssh port forwarding is also using another example of a networking tunnel, which allows you to transport packets securely from your localhost environment to a public network.

Ngrok

While there are many ways to create a networking tunnel, my favorite tool is Ngrok. After I downloaded the tool, I created a tunnel.bat script that’s available on the Windows PATH:

@echo off

call ngrok http %*

To open an HTTP or HTTPS tunnel, all I have to do is run the following command:

> tunnel 8080

ngrok by @inconshreveable

Session Status  online
Version         2.3.40
Region          United States (us)
Web Interface   http://127.0.0.1:4040
Forwarding      http‎://‎956e-188-24-86-235.ngrok‎.io 🡒 http://localhost:8080
Forwarding      https‎:/‎/956e-188-24-86-235.ngrok‎.io 🡒‎ http://localhost:808

Connections     ttl     opn     rt1     rt5     p50     p90
                0       0       0.00    0.00    0.00    0.00

That’s it!

Now, localhost:8080 is available at the 246d-188-24-86-235.ngrok.io‎ address. And the 246d-188-24-86-235.ngrok.io‎ uses an HTTPS tunnel to my localhost environment.

Testing time

To test how well the front-end performs, I now can use GT Metrix to analyze the Spring Boot server running on my localhost environment:

Tunnel localhost to the public Internet

When going to the NGrok command line window, I can see various metrics about the networking connections established via the tunnel:

Connections     ttl     opn     rt1     rt5     p50     p90
                24      0       0.00    0.01    0.24    32.28

Awesome, right?

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Conclusion

Exposing your localhost environment to a public Internet address is a very handy feature when testing a web application.

NGrok is a very simple tool that allows you to create a networking tunnel between your private web server and a public Internet address.

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