Any way to invoke code from VCL after a request has been serviced?

Ryan Burn rnickb731 at
Sat May 6 04:15:30 CEST 2017

>From VCL, is it possible to execute code that runs after a request has
been processed?

I'm looking into writing a module that enables Varnish for distributed
tracing using the OpenTracing project []. This requires
invoking code at the beginning of a request to start a span and insert
tracing context into the request's headers and invoking code after a
request's been processed to finish the span and measure how long it
took to process.

I recently did a similar project for nginx
[]. Nginx provides an
NGX_HTTP_LOG_PHASE [] that allows you
to set up handlers run after requests are serviced. Can anything
equivalent be done using VCL?

I image you could accomplish this by subscribing and regularly reading
from Varnish's shared memory log, but I'd much rather do it directly
if possible.

Thanks, Ryan

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