Varnish (Webproxy)

This role provides Varnish Cache, the high-performance HTTP accelerator, in the latest version provided by NixOS which is 7.4.x at the moment.

How we differ from what you are used to

Here is how we differ from what you already know from common Linux distributions and how you are used to configure, start, stop and maintain these packages.

• configuration file locations:

  Since we use NixOS, configuration files have to be edited in /etc/local/nixos, followed by a NixOS rebuild which copies them into the Nix store and activates the new configuration. To do so, run the command sudo fc-manage --build.

• service control:

  We use systemd to control processes. You can use familiar commands like sudo systemctl restart varnish to control services. However, remember that invoking sudo fc-manage --build is necessary to put configuration changes into effect. A simple restart is not sufficient. For further information, also see Local Configuration.

Role configuration

The role currently supports two different ways to configure Varnish. Please note that all configuration has to be performed as a service user.

The recommended way is to use Nix. For an overview of the available configuration options, see the Varnish module in our infrastructure repository. As with all NixOS modules, put your configuration into an appropriately named file in the /etc/local/nixos directory, e.g. /etc/local/nixos/varnish.nix.

You can also put your verbatim Varnish configuration into /etc/local/varnish/default.vcl. Please note that this way of configuring Varnish is deprecated and will likely be removed in the future.

The role passes a handful of command line arguments to Varnish to ensure reasonable default behaviour. If you wish to pass extra command line arguments to Varnish, then you should use the provided flyingcircus.services.varnish.extraCommandLine NixOS option. Arguments specified using this option (which may be defined multiple times) will be merged into the list of arguments passed to Varnish along with the role defaults.

Monitoring

• We monitor that the varnishd process is running.

• Please add a custom http checks which suite your needs to to /etc/local/sensu-client, for instance:

  {
    "varnish": {
      "command": "check_http -H localhost -p 8080",
      "notification" : "varnish broken",
      "interval": 120,
      "standalone": true
    }
  }