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This branch is for varnish post 7.2


This module provides a varnish director for dynamic creation of backends based on calls to

  • the system's network address resolution service which, in turn, typically use information from the /etc/hosts file and the Domain Name Service (DNS), but can be configured to use other sources like LDAP (see :ref:`nsswitch.conf(5)`).
  • or more advanced DNS resolution where getdns is available.

While standard varnish backends defined in VCL may also be defined in terms of host names, changes of the name service information will only be picked up with a VCL reload.

In contrast, for dynamic backends provided by this module,

  • name resolution information will be refreshed by background threads after a configurable time to live (ttl) or after the ttl from DNS with a getdns `vmod_dynamic.resolver`_.
  • resolution to multiple network addresses is supported

In addition, with a getdns `vmod_dynamic.resolver`_, service discovery by DNS SRV records is possible, in which case this module also allows to configure host names (targets), their ports, priority and weight though DNS. See for a good basic explanation and `vmod_dynamic.director.service`_ for details.

Further documentation is available in the manual page vmod_dynamic(3).


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.

For extended resolver functionality, getdns is required both during installation and at runtime. Before building, install getdns from source or install developer packages, e.g.:

apt-get install libgetdns-dev

At runtime, only the library itself is required, e.g.:

apt-get install libgetdns1

Building requires the Varnish header files and uses pkg-config to find the necessary paths.



If you have installed Varnish to a non-standard directory, call and configure with PKG_CONFIG_PATH pointing to the appropriate path. For instance, when varnishd configure was called with --prefix=$PREFIX, use

export PKG_CONFIG_PATH=${PREFIX}/lib/pkgconfig
export ACLOCAL_PATH=${PREFIX}/share/aclocal

The module will inherit its prefix from Varnish, unless you specify a different --prefix when running the configure script for this module.

Make targets:

  • make - builds the vmod.
  • make install - installs your vmod.
  • make check - runs the unit tests in src/tests/*.vtc.
  • make distcheck - run check and prepare a tarball of the vmod.

If you build a dist tarball, you don't need any of the autotools, only pkg-config and Varnish. You can build the module simply by running:


For the test suite to work, please add this line to your /etc/hosts: www.localhost img.localhost

then run:

make check

Also, the service tests require direct access to public DNS (for now).

Alternatively, the make check can also be skipped.

You can then proceed with the installation:

sudo make install

Installation directories

By default, the vmod configure script installs the built vmod in the directory relevant to the prefix. The vmod installation directory can be overridden by passing the vmoddir variable to make install.


FreeBSD users may install from either the ports tree or via packages:

  • via the Ports Tree

    cd /usr/ports/www/varnish-libvmod-dynamic/ && make install clean

  • via the Package

    pkg install varnish-libvmod-dynamic


Binary, debuginfo and source RPMs for VMOD dynamic are available at:

The packages are built for Enterprise Linux 7 (el7), and hence will run on compatible distros (such as RHEL7, Fedora, CentOS 7 and Amazon Linux).

To set up your YUM repository for the RPMs:

yum-config-manager --add-repo

The RPMs are compatible with Varnish versions 6.3.2 and 6.4.0. They also require the getdns library, as discussed above. The library is not necessarily available in the distributions' standard repositories, but can be installed from EPEL7:

yum install

If you have problems or questions concerning the RPMs, post an issue to one of the source repository web sites, or contact <>.

See also

If you want to learn more about DNS, you can start with RFC 1034 and other RFCs that updated it over time. You may also have DNS already in place, or may be interested in setting up a name server in your infrastructure. Below is a non-exhaustive list of tools and services, but for free software name servers you can have a look at debianadmin.

DNS in the cloud (in alphabetic order):

DNS and containers (in alphabetic order):


We thank the various people and companies having made vmod_dynamic a reality:

vmod_dynamic is based upon vmod_named developed and maintained from 2015 to 2017 by Dridi Boukelmoune (github @dridi) and supported by Varnish Software.

Maintenance and improvements 2017 - 2019 were sponsored by various unnamed UPLEX clients and authored by Geoffrey Simmons and Nils Goroll from UPLEX.

SRV record support and getdns integration in 2019 was supported by

vmod_dynamic also contains contributions by: Ricardo Nabinger Sanchez, Ryan Steinmetz