SearchVCL is a powerful and flexible cache configuration language, but out of the box it only offers you the tools to handle requests, responses, objects, session information, and VCL state transitions.
For all other things, you rely on VMODs. Your Varnish installation comes with a set of in-tree VMODs that were purposely kept outside of the core code.
All the cool integrations are done using VMODs; everything related to decision-making on the edge uses VMODs.
Now you certainly realize that there is a VMOD ecosystem that has various types of stakeholders in it: the Varnish Cache team, Varnish Software’s development team, and even individuals in the community.
Getting access to those modules shouldn’t be a frightening endeavor at all: sometimes there are distro packages, certain modules are in-tree and shipped by default. If you use Varnish Enterprise, all the enterprise VMODs and a collection of open source VMODs are already installed as part of the product.
And if none of these things apply to you: compiling VMODs from source is pretty straightforward. There will usually be line-by-line instructions on how to build and install the VMOD on your computer.
Hopefully this chapter was an eye opener. But now it’s time to turn the page, and go to the next chapter. In chapter 6, we’ll cover cache invalidation, which is all about removing objects from cache. We’ll even use some VMODs for that.