What is VCL?
What is VCL? What are VMODs?
Varnish Configuration Language (VCL) is a domain-specific language designed for use inside of Varnish Cache. VCL allows users to configure Varnish Cache exactly how they see fit. It gives total control of content caching policies, HTTP behavior, and routing. When a VCL configuration is loaded, Varnish Cache translates the VCL code to C and compiles it to a shared object, which is then dynamically linked back into Varnish Cache.
VMODs are Varnish Cache modules that add new functionality to VCL. A VMOD is a shared library written in C, which is loaded into Varnish Cache and then callable from VCL. VMODs are one of the factors that make Varnish Cache and VCL so effective. VMODs can introduce a wide variety of new features and functionality to Varnish Cache, greatly increasing the power of VCL.
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