Vmod-goto: your go-to guy for dynamic backends

In Dridi's post, you learned about Varnish's technical choices regarding backends, and why a VMOD was necessary. If you didn't read the article (shame on you), here's the recap:

  • Varnish resolves domain names and IP when compiling the VCL, so the resolved address is set in stone.
  • And there must be exactly one resolved address, if the domain name is not found, or is served by multiple IPs, the VCL won't load.
  • You can work around this with a cron'd script, periodically generating a VCL with the correct and updated addresses.
  • However, this forces you to garbage-collect the old VCL; you'll have to take extra care of the probes and you'll reset the backend stats everytime you reload since backends are tied to the VCL.
  • So we built a VMOD.

And that VMOD is named "named", another proof that engineers shouldn't be allowed to name things.

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11/23/16 1:03 PM
by Guillaume Quintard

Varnish Software Blog




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