Скачать или смотреть Fixing Empty reply from server Error with Varnish & Hitch on Ubuntu 20.04

Learn how to solve the `empty reply from server` issue caused by configuration errors between Varnish and Hitch on Ubuntu 20.04. This step-by-step guide will help you resolve the problem easily.
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This video is based on the question https://stackoverflow.com/q/70656894/ asked by the user 'Amir' ( https://stackoverflow.com/u/6354861/ ) and on the answer https://stackoverflow.com/a/70662862/ provided by the user 'Thijs Feryn' ( https://stackoverflow.com/u/12892695/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the Empty Reply from Server Issue

If you're working with a setup that utilizes Varnish as a caching server and Hitch for SSL termination on an Ubuntu 20.04 server, you may have encountered a frustrating error message:

[[See Video to Reveal this Text or Code Snippet]]

This problem often arises due to misconfigurations between Varnish and Hitch, especially when using the PROXY protocol. In this article, we'll walk you through the steps to resolve this issue, enabling smooth communication between your servers.

The Configuration Setup

To give you some context, here's a quick summary of your setup:

Server 1 (s1): Responsible for applications, IP - 192.168.1.105

Server 2 (s2): Acts as a separate cache server, IP - 192.168.1.106

After installing Varnish and Hitch on your cache server (s2), you made the following modifications:

Adjusted the default.vcl file to point to s1.

Set up hitch.conf to listen on port 443 and forward requests to Varnish on port 8443.

Diagnosing the Problem

The error you faced indicates that when trying to call your site with a simple curl command:

[[See Video to Reveal this Text or Code Snippet]]

You received an empty response from the server, which means that while the request was received, it wasn't processed correctly. Additionally, running the Varnish log command:

[[See Video to Reveal this Text or Code Snippet]]

led to an error stating that Varnish couldn't connect. This often indicates that Varnish is not receiving the expected information.

Solution Steps

Let’s explore the solutions step-by-step to fix the empty reply from server issue.

1. Enable PROXY Protocol in Hitch

To start, you need to enable the PROXY protocol in your hitch.conf file. You'll want to uncomment the following line:

[[See Video to Reveal this Text or Code Snippet]]

By doing this, you're allowing Hitch to send client connection information to Varnish, which is essential for processing requests.

2. Make Varnish Protocol Aware

Next, it is crucial for Varnish to understand the protocol being used (HTTP or HTTPS). You can achieve this by utilizing the vmod_proxy module. Add the following code to your default.vcl:

[[See Video to Reveal this Text or Code Snippet]]

This code ensures that Varnish caches versions of your responses based on whether the original request was made over HTTP or HTTPS.

3. Bonus: Enable HTTP/2 Support

If you want to enhance your server's performance further, you might consider enabling HTTP/2. In your hitch.conf, uncomment the line for ALPN protocols:

[[See Video to Reveal this Text or Code Snippet]]

You will then need to ensure that Varnish supports HTTP/2 by adding the following parameter to your varnishd configuration:

[[See Video to Reveal this Text or Code Snippet]]

4. Restart Both Services

The final step is to restart both Hitch and Varnish to apply your changes. You can do this with the following commands:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

Solving the empty reply from server issue involves properly configuring communication between Varnish and Hitch by enabling the PROXY protocol, making Varnish protocol aware, and optionally enabling HTTP/2 for enhanced performance. Following these steps should allow you to successfully receive responses from your server and significantly improve your caching setup.

By correcting these configurations, you can ensure that your Varnish caching server and Hitch SSL termination are hopping along smoothly, providing your clients with the best possible experience.

Feel free to reach out if you need further assistance!