vmod_backendhealth

Varnish Backend Health Module

Author:	Dag Haavi Finstad
Date:	2013-12-13
Version:	1.0
Manual section:	3

SYNOPSIS

import backendhealth;

DESCRIPTION

A vmod that lets you query your Varnish server for a JSON object with the health status of your backends. With the accompanied VCL code, visiting the URL /backend_health on the Varnish server will produce an application/json response of the following format:

{
    "default": "healthy",
    "b1": "sick",
    "www": "healthy"
}

The health status is determined from the same method as if you were to check req.backend.healthy for each specific backend in VCL.

Please see the VCL in the example below (also provided in file example.vcl). JSONP is also supported, by providing an additional ?callback=foo query string.

FUNCTIONS

json

Prototype:

json(BOOL formatted)

Return value

STRING

Description

Returns a JSON object with tuples of "backend name": "health status". Parameter decides if you get neatly formatted JSON or not, "true" or "false".

Example:

sub vcl_recv {
    if (req.url ~ "/backend_health") {
        error 777 "OK";
    }
}

sub vcl_error {
    if (obj.status == 777) {
        set obj.status = 200;

        # JSONP
        if (req.url ~ "\?callback=\w+") {
            set req.http.cb = regsub(req.url, ".*\?callback=(\w+).*", "\1");
            set obj.http.Content-Type = "application/javascript";
            synthetic req.http.cb + {"("} + backendhealth.json(false) + {")"};
        }

        # JSON
        else {
            set obj.http.Content-Type = "application/json";
            synthetic backendhealth.json(true);
        }

        return (deliver);
    }
}

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.

Usage:

./configure VARNISHSRC=DIR [VMODDIR=DIR]

VARNISHSRC is the directory of the Varnish source tree for which to compile your vmod. Both the VARNISHSRC and VARNISHSRC/include will be added to the include search paths for your module.

Optionally you can also set the vmod install directory by adding VMODDIR=DIR (defaults to the pkg-config discovered directory from your Varnish installation).

Make targets:

• make - builds the vmod
• make install - installs your vmod in VMODDIR
• make check - runs the unit tests in src/tests/*.vtc

In your VCL you could then use this vmod by extending it along the lines of the above example.

COPYRIGHT

This document is licensed under the same license as the libvmod-backendhealth project. See LICENSE for details.

• Copyright (c) 2011 Varnish Software