What is VCL?
What are VMODs? What is the Varnish Configuration Language?
The Varnish Configuration Language (VCL) is a small domain-specific language designed to be used to define request handling and document caching policies for the Varnish HTTP accelerator. When a new configuration is loaded, the varnishd management process translates the VCL code to C and compiles it to a shared object which is then dynamically linked into the server process.
VMODs (Varnish modules) are extensions written in VCL for use in Varnish Cache. A VMOD is a shared library with some C functions that can be called from VCL code. VMODs are one of the factors that make Varnish Cache so effective; VCL is flexible and can be used to create discrete functions, making it an easy-to-use and maintain option for organizations that need to create custom modules.
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