Varnish Agent
Roff C JavaScript Shell HTML CSS Other
Latest commit e6e3e3c Mar 3, 2017 @hugocruz hugocruz Added installation link



Varnish Agent

Manual section:1
Authors:Kristian Lyngstøl, Yves Hwang, Dag Haavi Finstad


varnish-agent [-C cafile] [-c port] [-d] [-g group] [-H directory]
              [-h] [-k allow-insecure-vac] [-K agent-secret-file]
              [-n name] [-P pidfile] [-p directory] [-q] [-r]
              [-S varnishd-secret-file] [-T host:port] [-t timeout]
              [-u user] [-V] [-v] [-z vac_register_url]


The varnish-agent is a small daemon meant to communicate with Varnish and other varnish-related services to allow remote control and monitoring of Varnish.

It listens to port 6085 by default. Try http://hostname:6085/html/ for the HTML front-end. All arguments are optional. The Varnish Agent will read all the necessary options from the shm-log, with the exception of the username and password, which is read from the -K option or the default value.

For default values of options, including but not limited to where username and password is read from (-K), where VCL is saved to (-p) and where HTML is read from (-H), see varnish-agent -h.



-C cafile CA certificate for use by the cURL module. For use when the VAC register URL is specified as https using a certificate that can not be validated with the certificates in the system's default certificate directory.
-c port Port number to listen for incoming connections. Defaults to 6085.
-d Run in foreground.
-g group Group to run as. Defaults to varnish.
-H directory Specify where html files are found. This directory will be accessible through /html/. The default provides a proof of concept front end.
-h Print help.
-k allow-insecure-vac
 This option explicitly allows curl to perform 'insecure' SSL connections and transfers.
-K agent-secret-file
 Path to a file containing a single line representing the username and password required to authenticate. It should have a format of username:password.
-n name Specify the varnish name. Should match the varnishd -n option. Amongst other things, this name is used to construct a path to the SHM-log file.
-P pidfile Write pidfile.
-p directory Specify persistence directory. This is where VCL is stored.
-q Quiet mode. Only log/output warnings/errors.
-r Read-only mode. Only accept GET, HEAD and OPTIONS request methods.
-S varnishd-secret-file
 Path to the shared secret file, used to authenticate with varnish.
-T hostport Hostname and port number for the management interface of varnish.
-t timeout Timeout in seconds for talking to varnishd.
-u user User to run as. Defaults to varnish.
-V Print version.
-v Verbose mode. Be extra chatty, including all CLI chatter.
-z vac_register_url
 Specify the callback vac register url.


The agent does not require Varnish configuration changes for most changes. However, if you wish to boot Varnish up with the last known VCL, you may tell Varnish to use /var/lib/varnish-agent/boot.vcl. E.g by modifying /etc/sysconfig/varnish or /etc/default/varnish and changing the -f argument.


Keep it simple.

Everything is written as a module, and the goal is:

  • Close to 0 configuration
  • "Just works"
  • Maintainable
  • Generic
  • Stateless


  • varnishadm(1)
  • varnishd(1)
  • varnishlog(1)
  • varnishstat(1)
  • varnish-cli(7)
  • vcl(7)


The first generic WebUI for Varnish was written by Petter Knudsen of Linpro AS in 2009. This led to the creation of the Varnish Administration Console, built to manage multiple Varnish instances. Until 2013, the Varnish Administration Console used a minimal wrapper around the Varnish CLI language, requiring that the Varnish Administration Console knew the CLI language. This wrapper was known as the Varnish Agent version 1, written by Martin Blix Grydeland.

Development of the Varnish Agent version 2 begun in late 2012, with the first release in early 2013. Unlike the first version, it exposes a HTTP REST interface instead of trying to simulate a Varnish CLI session.


The agent is multi-threaded, but the HTTP listener is not. As such, the agent is vulnerable to DOS by any slow client. This should not be a problem if you are using it internally, and if you are exposing it to the public, consider sticking it behind Varnish itself (and consider read-only mode with -r).

Trying to "use" the boot VCL will regularly cause a "VCL deployed OK but not persisted". This is because the agent can only persist VCL if the VCL was stored through the agent - the boot vcl was not stored through the agent so there is no matching auto-generated VCL for it on disk. Workaround: Don't re-use the boot VCL.

The vlog module is limited and the filter largely broken after the Varnish 4.0 API changes.

You may also want to add some SSL on top of it. The agent provides HTTP Basic authentication, but that is in no way secure as credentials are easy to extract to anyone listening in.

For more, see


This document is licensed under the same license as the Varnish Agent itself. See LICENSE for details.

  • Copyright 2012-2015 Varnish Software Group