pinterest-deploy.vcl

#
# Example of pinterest.com -alike application deployment.
#
vcl 4.0;

import std;
import directors;
import cookie;
import header;
import var;

backend current1 { .host = "192.0.2.11"; .port = "8080"; }
backend current2 { .host = "192.0.2.12"; .port = "8080"; }
backend current3 { .host = "192.0.2.13"; .port = "8080"; }
backend current4 { .host = "192.0.2.14"; .port = "8080"; }

backend prev1 { .host = "192.0.2.11"; .port = "8081"; }
backend prev2 { .host = "192.0.2.12"; .port = "8081"; }
backend prev3 { .host = "192.0.2.13"; .port = "8081"; }
backend prev4 { .host = "192.0.2.14"; .port = "8081"; }


sub vcl_init {
    new rr1 = directors.round_robin();
    rr1.add_backend(current1); rr1.add_backend(current2);
    rr1.add_backend(current3); rr1.add_backend(current4);

    new rr2 = directors.round_robin();
    rr2.add_backend(prev1); rr2.add_backend(prev2);
    rr2.add_backend(prev3); rr2.add_backend(prev4);
}

sub vcl_recv {
    if (req.url ~ "^/upgrade/current") {
        var.global_set("prev", var.global_get("current"));
        var.global_set("current", req.http.new_version); // or regsub from req.url.
        return(synth(200, "OK"));
    } else if (req.url == "/rollback") {
        var.global_set("current", var.global_get("prev"));
    }

    if (req.http.AppVersion == var.global_get("current")) {
        set req.backend_hint = rr1.backend();
    } else if (req.http.AppVersion == var.global_get("prev")) {
        set req.backend_hint = rr2.backend();
    } else {
        # assumed that the (cached) backend response sets AppVersion since not set.
        if (std.random(0, 9) == 0) {
            set req.http.AppVersion = var.global_get("current");
        } else {
            set req.http.AppVersion = var.global_get("prev");
        }
    }
}