VMOD useful to dump customizable information about contents currently stored in the cache to a JSON file for subsequent analysis in order to consider better caching strategies.

Looking for official support for this VMOD? Please, contact Allenta Consulting, a Varnish Software Premium partner.

SYNOPSIS

import gossip;

Function VOID dump(STRING file, BOOL discard=1)

Function VOID discard()

Function STRING escape_json_string(STRING value)

EXAMPLE

/etc/varnish/default.vcl

vcl 4.0;

import gossip;
import std;

backend default {
    .host = "127.0.0.1";
    .port = "8080";
}

acl local_acl {
    "localhost";
}

sub vcl_recv {
    if (req.url ~ "^/gossip/(?:dump/.+|discard/)$") {
        if (client.ip ~ local_acl) {
            if (req.url ~ "^/gossip/dump/.+") {
                set req.http.X-Gossip-File = regsub(
                    regsub(req.url, "^/gossip/dump", ""),
                    "\?.*$",
                    "");
                if (req.url ~ "[?&]discard=[^&]*") {
                    set req.http.X-Gossip-Discard = regsub(
                        req.url,
                        "^.*[?&]discard=([^&]*).*$",
                        "\1");
                }
                gossip.dump(
                    req.http.X-Gossip-File,
                    std.integer(req.http.X-Gossip-Discard, 1) > 0);
                return (synth(200, "Now dumping."));
            } elsif (req.url == "/gossip/discard/") {
                gossip.discard();
                return (synth(200, "Discarded."));
            } else {
                return (synth(404, "Not found."));
            }
        } else {
            return (synth(405, "Not allowed."));
        }
    }
}

sub vcl_deliver {
    unset resp.http.X-Gossip-Info;
}

sub vcl_backend_response {
    set beresp.http.X-Gossip-Info =
        {"{"} +
        {""tst":"} + std.time2real(now, 0) + {","} +
        {""url":""} + gossip.escape_json_string(bereq.http.Host + bereq.url) + {"","} +
        {""device":""} + gossip.escape_json_string(bereq.http.X-Device) + {"","} +
        {""ip":""} + gossip.escape_json_string(client.ip) + {"""} +
        {"}"};

    set beresp.ttl = 1h;
    set beresp.grace = 24h;
}

Dump cache contents

$ curl http://127.0.0.1/gossip/dump/tmp/objects.json?discard=0

$ cat /tmp/objects.json
{"tst":0.000000,"now":1527154240.137104}
...
{"info":{"tst":1527154237.470,"url":"127.0.0.1/foo","device":"desktop","ip":"127.0.0.1"},"hits":42,"ttl":3597.545651,"grace":86400.000000,"keep":0.000000}
{"info":{"tst":1527154237.483,"url":"127.0.0.1/bar","device":"desktop","ip":"127.0.0.1"},"hits":314,"ttl":3597.651994,"grace":86400.000000,"keep":0.000000}
{"info":{"tst":1527154237.494,"url":"127.0.0.1/bar","device":"mobile","ip":"127.0.0.1"},"hits":271,"ttl":3597.558113,"grace":86400.000000,"keep":0.000000}

$ curl http://127.0.0.1/gossip/dump/tmp/objects.json?discard=1

$ cat /tmp/objects.json
{"tst":0.000000,"now":1527154241.506256}
...
{"tst":1527154237.470,"url":"127.0.0.1/foo","device":"desktop","ip":"127.0.0.1"}
{"tst":1527154237.483,"url":"127.0.0.1/bar","device":"desktop","ip":"127.0.0.1"}
{"tst":1527154237.494,"url":"127.0.0.1/bar","device":"mobile","ip":"127.0.0.1"}

INSTALLATION

The source tree is based on autotools to configure the building, and does also have the necessary bits in place to do functional unit tests using the varnishtest tool.

Beware this project contains multiples branches (master, 4.1, etc.). Please, select the branch to be used depending on your Varnish Cache version (Varnish trunk → master, Varnish 4.1.x → 4.1, etc.).

COPYRIGHT

See LICENSE for details.

BSD's implementation of the red–black tree and the splay tree data structures by Niels Provos has been borrowed from the Varnish Cache project:

• https://github.com/varnishcache/varnish-cache/blob/master/include/vtree.h

Copyright (c) Carlos Abalde <carlos.abalde@gmail.com>