Nagios

Nagios is a monitoring daemon. It comprises the daemon itself, and a web interface.

Daemon configuration

The simplest way of having the Nagios daemon run is to write its configuration in a main.cfg alongside configuration.nix in /etc/nixos.

Then

/etc/nixos/configuration.nix

{config, pkg, lib, ...}
{
   # [...]
   services.nagios = {
      enable = true;
      objectDefs = [ ./main.cfg ];
   };
}

Tip

In order to affect your system by your nix-language-specific changes you have to evaluate it, run (as root):

# nixos-rebuild switch

Nagios configuration files contain a lot of boilerplate, it is possible to reuse some of the default configuration files. For example to reuse templates.cfg, timeperiods.cfg and commands.cfg:

{
    services.nagios.objectDefs =
      (map (x: "${pkgs.nagios}/etc/objects/${x}.cfg") [ "templates" "timeperiods" "commands" ]) ++
      [ ./main.cfg ];
}

To enable verbose logging into /var/log/nagios/debug.log:

{
    services.nagios.extraConfig = {
        debug_level = "-1";
        debug_file = "/var/log/nagios/debug.log";
     };
}

Web interface

The NixOS module for Nagios does not automatically configure the web interface for your favorite web server. The section below describes a possible configuration for Nginx.

The web interface does not handle authentication; instead it is delegated to the web server. We will use HTTP basic authentication. This is only safe over HTTPS, of course. You need to create a htpasswd file readable by the nginx user only:

htpasswd -c /var/lib/nagios/htpasswd admin_account
chmod 0440 /var/lib/nagios/htpasswd
chown nginx:nginx /var/lib/nagios/htpasswd 

Now a possible configuration looks like this:

/etc/nixos/configuration.nix

{config, pkgs, lib, ...}:
{
     # [...]
     services.phpfpm.pools.nagios = {
        user = "nagios";
        settings = {
          "listen.owner" = config.services.nginx.user;
          "pm" = "ondemand";
          "pm.max_children" = 2;
          "pm.process_idle_timeout" = "60s";
          "pm.max_requests" = 200;
        };
      };
      services.fcgiwrap = {
        enable = true;
        user = "nagios";
      };
      services.nginx.virtualHosts."nagios.example.com" = {
        forceSSL = true;
        enableACME = true;
        root = "${pkgs.nagios}/share/";
        extraConfig = ''
          index index.php;
          auth_basic "Nagios";
          auth_basic_user_file /var/lib/nagios/htpasswd;
        '';
        locations = {
          "/".tryFiles = "$uri /index.php";
          "/nagios/".alias = "${pkgs.nagios}/share/";
          "~ \\.cgi$" = {
            root = "${pkgs.nagios}/sbin/";
            extraConfig = ''
              rewrite ^/nagios/cgi-bin/(.*)$ /$1;

              include ${pkgs.nginx}/conf/fastcgi.conf;
              include ${pkgs.nginx}/conf/fastcgi_params;

              fastcgi_param AUTH_USER       $remote_user;
              fastcgi_param REMOTE_USER     $remote_user;
              fastcgi_param SCRIPT_FILENAME ${pkgs.nagios}/share/sbin$fastcgi_script_name;  

              fastcgi_pass unix:${config.services.fcgiwrap.socketAddress};
            '';
          };
          "~* \\.php$" = {
            tryFiles = "$uri =404";
            extraConfig = ''
              include ${pkgs.nginx}/conf/fastcgi_params;
              include ${pkgs.nginx}/conf/fastcgi.conf;
              fastcgi_split_path_info ^(.+\.php)(/.+)$;
              fastcgi_pass unix:${config.services.phpfpm.pools.nagios.socket};
              fastcgi_index index.php;
            '';
          };
        };
      };
}