Practical VCL limits; giant URL->backend map

Per Buer perbu at
Tue Mar 1 08:45:03 CET 2011

On Tue, Mar 1, 2011 at 1:09 AM, Gordon Mohr <gojomo at> wrote:
> The quite-possibly-nutty idea has occurred to me of auto-generating a VCL
> that maps each of about 18 million artifacts (incoming URLs) to 1,2,or3 of
> what are effectively 621 backend locations. (The mapping is essentially
> arbitrary.)


> Essentially, it would be replacing a squid url_rewrite_program.
> Am I likely to hit any hard VCL implementation limits (in
> depth-of-conditional-nesting, overall size, VCL compilation overhead, etc.)
> if my VCL is ~100-200MB in size?
> Am I overlooking some other more simple way to have varnish consult an
> arbitrary mapping (something similar to a squid url_rewrite_program)?

Yeah. Take a look at the DNS director. Just put your backends in a
zone, point Varnish at it and Bob's your uncle.

Per Buer, Varnish Software
Phone: +47 21 98 92 61 / Mobile: +47 958 39 117 / Skype: per.buer
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