List Varnish VMODs: Command-Line Guide

Aug 14, 2025 by Benjamin Cohen 39 views

How to List Installed Varnish VMODs from the Command Line

Hey guys! Ever wondered how to check which Varnish VMODs (Varnish Modules) you have installed and loaded? It's a common question, especially when you're trying to optimize your Varnish setup or troubleshoot issues. In this article, we'll dive deep into the command-line methods for listing your Varnish VMODs. We’ll break it down step by step, making it super easy to follow along. Whether you're a seasoned Varnish pro or just starting out, this guide will help you get a handle on managing your VMODs. Let's jump right in!

Understanding Varnish VMODs

First off, let's talk about what Varnish VMODs actually are. Think of them as plugins for Varnish Cache, the powerful open-source HTTP accelerator. VMODs extend Varnish’s functionality, allowing you to do cool things like manipulating HTTP headers, implementing custom caching logic, or even integrating with other services. They're essential for tailoring Varnish to your specific needs and optimizing performance.

The real power of Varnish comes from its extensibility, and that’s where VMODs shine. They let you customize Varnish's behavior far beyond its default capabilities. For example, you might use a VMOD to implement geo-based routing, modify cache keys, or add security features. Without VMODs, you'd be stuck with a more generic caching solution, which might not fit your unique requirements. So, understanding and managing your VMODs is crucial for getting the most out of Varnish.

Now, why would you want to list your installed VMODs? Well, there are several reasons. Maybe you're debugging an issue and need to verify that a specific VMOD is loaded. Or perhaps you're auditing your Varnish configuration and want to get an overview of all the extensions you're using. Keeping track of your VMODs helps you maintain a clean, efficient, and secure Varnish setup. Plus, knowing which VMODs are in use is super helpful when you're collaborating with others or handing off a project.

Methods to List Installed VMODs

Alright, let's get to the nitty-gritty. How do you actually list those Varnish VMODs from the command line? There are a couple of ways to do this, and we'll cover the most common and effective methods. Each approach has its own advantages, so you can choose the one that best fits your workflow.

Method 1: Using `varnishd -V`

The simplest way to get a list of compiled-in VMODs is by using the varnishd -V command. This command displays the Varnish version along with other build-time information, including the VMODs that were compiled into the Varnish binary. It's a quick and easy way to see what's available without digging through configuration files.

Here's how it works:

Open your terminal.
Type varnishd -V and press Enter.

The output will show the Varnish version and a list of compiled-in VMODs. This method is great for a quick overview, but it only shows VMODs that were compiled directly into Varnish. If you're using dynamically loaded VMODs, they won't appear in this list. Still, it’s a good starting point for understanding your Varnish setup.

Method 2: Examining Varnish Configuration Files

Another way to list VMODs is by examining your Varnish configuration files, typically located in /etc/varnish/default.vcl. This method shows you which VMODs are actually being used in your Varnish configuration. It's more comprehensive than varnishd -V because it includes dynamically loaded VMODs.

Follow these steps:

Open your terminal.
Use a text editor like nano or vim to open your Varnish configuration file:
```
sudo nano /etc/varnish/default.vcl
```
Search for lines that start with import. These lines declare the VMODs being used in your configuration.

For example, you might see lines like:

import std;
import vcl_acl;
import xkey;

Each import statement indicates a VMOD that Varnish will load and use. This method gives you a clear picture of which VMODs are active in your Varnish instance. It’s especially useful for troubleshooting and making sure you have the correct VMODs loaded for your configuration.

Method 3: Using `varnishadm vcl.show`

For a more dynamic view of loaded VMODs, you can use the varnishadm vcl.show command. This command displays the currently loaded VCL (Varnish Configuration Language) configuration, which includes the import statements for VMODs. It's a great way to see the active VMODs in real-time, especially if you're making frequent configuration changes.

Here’s how to use it:

Open your terminal.
Connect to the Varnish administration interface:
```
varnishadm -T 127.0.0.1:6082 -S /etc/varnish/secret
```
(Replace 127.0.0.1:6082 and /etc/varnish/secret with your Varnish admin address and secret file path if they are different.)
Run the vcl.show command:
```
vcl.show
```
The output will include your VCL configuration, where you can find the import statements listing the VMODs.
Type quit to exit the Varnish administration interface.

This method provides a real-time view of your active VMODs, making it super handy for dynamic environments where configurations change frequently. It’s also great for scripting and automation, as you can easily parse the output to extract VMOD names.

Practical Examples and Troubleshooting

Okay, let’s make this even more practical with some examples and troubleshooting tips. Knowing how to list VMODs is one thing, but understanding how to use that information is where the real power lies. We’ll walk through some common scenarios and how to handle them.

Scenario 1: Verifying a VMOD Installation

Let’s say you’ve just installed a new VMOD and want to make sure it’s properly loaded. You can use the methods we discussed to verify this.

Steps:

First, use varnishd -V to see if the VMOD was compiled into Varnish. If it’s there, great!
Next, check your default.vcl file to make sure you’ve added the import statement for the VMOD.
Finally, use varnishadm vcl.show to confirm that the VMOD is loaded in the active configuration.

If the VMOD shows up in all three places, you’re good to go. If not, you might need to revisit your installation steps or check your configuration file for errors.

Scenario 2: Debugging Varnish Behavior

VMODs can sometimes cause unexpected behavior if they’re not configured correctly or if there are conflicts between VMODs. Listing your VMODs can help you narrow down the source of the problem.

Troubleshooting Steps:

Use varnishadm vcl.show to see the currently loaded VMODs.
If you're experiencing issues, try commenting out VMODs one by one in your default.vcl file and reloading Varnish to see if the problem goes away. This can help you identify the problematic VMOD.
Check the VMOD’s documentation for any known issues or configuration tips.

By systematically checking and disabling VMODs, you can often pinpoint the root cause of Varnish issues and get your setup running smoothly again.

Scenario 3: Auditing Your Varnish Configuration

Regularly auditing your Varnish configuration is a good practice for security and performance. Listing your VMODs is an important part of this process.

Audit Steps:

Use varnishadm vcl.show to get a list of all active VMODs.
Review each VMOD and make sure you understand its purpose and configuration.
Remove any VMODs that are no longer needed or that you’re not actively using. This helps keep your configuration clean and reduces the risk of security vulnerabilities.

Regular audits ensure your Varnish setup remains efficient and secure over time. It’s a bit like spring cleaning for your server!

Best Practices for Managing Varnish VMODs

To wrap things up, let’s talk about some best practices for managing your Varnish VMODs. Following these tips will help you keep your Varnish setup healthy and efficient.

1. Keep VMODs Updated

Just like any software, VMODs can have bugs and security vulnerabilities. Make sure you’re using the latest versions of your VMODs to benefit from bug fixes and security patches. Check the VMOD’s documentation or repository for update instructions.

2. Document Your VMOD Usage

It’s a good idea to document which VMODs you’re using and why. This makes it easier to troubleshoot issues, collaborate with others, and maintain your Varnish setup over time. A simple comment in your default.vcl file can go a long way.

3. Test VMODs in a Staging Environment

Before deploying changes to your production environment, always test them in a staging environment. This includes adding, removing, or updating VMODs. Testing helps you catch any issues before they impact your live traffic.

4. Use Version Control

Keep your Varnish configuration files, including your default.vcl, in a version control system like Git. This makes it easy to track changes, revert to previous versions, and collaborate with others. Version control is a lifesaver when things go wrong.

5. Monitor Varnish Performance

Keep an eye on your Varnish performance after making changes to your VMODs. Use tools like varnishstat and varnishlog to monitor cache hit ratios, response times, and other metrics. This helps you ensure that your VMODs are improving performance, not hindering it.

Conclusion

So, there you have it! Listing your Varnish VMODs from the command line is a crucial skill for anyone working with Varnish Cache. Whether you're using varnishd -V, examining your configuration files, or using varnishadm vcl.show, you now have the tools to see exactly which VMODs are loaded in your Varnish instance. By understanding and managing your VMODs effectively, you can optimize your Varnish setup, troubleshoot issues, and keep your caching layer running smoothly. Keep these tips and tricks handy, and you’ll be a Varnish VMOD master in no time! Happy caching, guys!