Can we perform mapping or do a lookup of string or KV pair in Varnish `sub vcl_recv`

Question

I am trying to route the traffic/connections to backend director based on url parameters which are passed on incoming request.

Here is my current config

sub vcl_recv {
    if (req.url ~ "sto") {
        set req.backend_hint = endpoint1.backend();
    } 
}

Currently, above config does static mapping/check for sto. I would like to do a dynamic lookup from map/hash/KV file and do condition check with url contents.

Here is how I do it in haproxy

    use_backend %[path,map_sub(/etc/haproxy/GET.map)]

#>cat GET.map
# url paramter      backend location/name
/sgtier             get_backend1
/sto                get_backend2

Config file

vcl 4.0;
import directors;


backend sg_gw1 {
    .host = "1.8.4.4";
    .port = "1043";
}

backend tss_gw1 {
    .host = "1.8.13.2";
    .port = "8080";
}


sub vcl_recv {
    if (req.url ~ "sto") {
       set req.backend_hint = sg_gw1;
    }
    elsif (req.url ~ "common") {
        set req.backend_hint = tss_gw1;
    }
}

Answer 1

Dynamic backends are supported in Varnish Enterprise. See https://docs.varnish-software.com/varnish-cache-plus/vmods/goto/ for more information.

An open source alternative for dynamic backends can be found on https://code.uplex.de/uplex-varnish/libvmod-backend_dyn