At 99designs we heavily (ab)use Varnish to make our app super fast, but also to do common, simple tasks without having to invoke our heavy-by-contrast PHP stack. As a result, our Varnish config is pretty involved, containing more than 1000 lines of VCL, and a non-trivial amount of embedded C. When we started seeing regular segfaults, it was a pretty safe assumption that one of us had goofed writing C code. So how do you track down a transient segfault in a system like Varnish? Join us down the rabbit hole… Get a core dump The first step is to modify your production environment to provide you with useful core dumps. There are a few steps in this: First of all, configure the kernel to provide core dumps by setting a few sysctls:
Continue reading %Debugging Varnish%
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