Varnish v1 -vcl+backend declares an instance of your real Varnish server and loads the VCL code inside the brackets. start can also be at a later point in your code as server s1 -start. The -start directive makes an instance of that declaration to be started. Server s1 declares a simulated origin server that receives a request rxreq, and transmits a response txresp. When run, the above script simulates an origin server s1, starts a real Varnish instance v1, and simulates a client c1. VTC is not compiled but simply interpreted on the fly. Varnishtest does not follow the unit testing framework (up/test/assert/tear down) nor behavior-driven development (given/when/then).ĭepending on your use case, there might be test preparations, executions and assertions all over the place. Therefore, we introduce next varnishtest before proceeding with the implementation the VMOD itself. In fact, we recommend you first to write your tests as part of your design, and then implement your VMOD. When writing VMODs, you should test them towards varnishtest. In addition, VMODs do not require to reload VCL files to take effect. If you use the memory management API provided by Varnish, your VMODs are generally easier to maintain, more secure, and much easier to debug in collaboration with other developer. VCL allows you to add inline C code, but this is not the most convenient approach. However, sometimes you might need more functionalities, e.g., look up an IP address in a database. This language is very powerful and efficient for most tasks of a cache server. VCL is the domain specific language of Varnish. We have already used the std VMOD in this book to check whether a backend is healthy by calling std.healthy(). The standard (std) VMOD, for instance, is a VMOD included in Varnish Cache. A VMOD is a shared library with some C functions which can be called from VCL code.
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