nixos/munin: add extraPlugins and extraAutoPlugins options [#17895]

extraAutoPlugins lets you list plugins and plugin directories to be
autoconfigured, and extraPlugins lets you enable plugins on a one-by-one
basis. This can be used to enable plugins from contrib (although you'll
need to download and check out contrib yourself, then point these
options at it), or plugins you've written yourself.

1 files changed, 107 insertions, 1 deletions

diff --git a/nixos/modules/services/monitoring/munin.nix b/nixos/modules/services/monitoring/munin.nix
index 431d0397546..af3562befde 100644
--- a/nixos/modules/services/monitoring/munin.nix
+++ b/nixos/modules/services/monitoring/munin.nix
@@ -74,6 +74,46 @@ let
       ln -s ${pluginConf} $out/nixos-config
     '';
   };
+
+  # Copy one Munin plugin into the Nix store with a specific name.
+  # This is suitable for use with plugins going directly into /etc/munin/plugins,
+  # i.e. munin.extraPlugins.
+  internOnePlugin = name: path:
+    "cp -a '${path}' '${name}'";
+
+  # Copy an entire tree of Munin plugins into a single directory in the Nix
+  # store, with no renaming.
+  # This is suitable for use with munin-node-configure --suggest, i.e.
+  # munin.extraAutoPlugins.
+  internManyPlugins = name: path:
+    "find '${path}' -type f -perm /a+x -exec cp -a -t . '{}' '+'";
+
+  # Use the appropriate intern-fn to copy the plugins into the store and patch
+  # them afterwards in an attempt to get them to run on NixOS.
+  internAndFixPlugins = name: intern-fn: paths:
+    pkgs.runCommand name {} ''
+      mkdir -p "$out"
+      cd "$out"
+      ${lib.concatStringsSep "\n"
+          (lib.attrsets.mapAttrsToList intern-fn paths)}
+      chmod -R u+w .
+      find . -type f -exec sed -E -i '
+        s,(/usr)?/s?bin/,/run/current-system/sw/bin/,g
+      ' '{}' '+'
+    '';
+
+  # TODO: write a derivation for munin-contrib, so that for contrib plugins
+  # you can just refer to them by name rather than needing to include a copy
+  # of munin-contrib in your nixos configuration.
+  extraPluginDir = internAndFixPlugins "munin-extra-plugins.d"
+    internOnePlugin nodeCfg.extraPlugins;
+
+  extraAutoPluginDir = internAndFixPlugins "munin-extra-auto-plugins.d"
+    internManyPlugins
+    (builtins.listToAttrs
+      (map
+        (path: { name = baseNameOf path; value = path; })
+        nodeCfg.extraAutoPlugins));
 in
 
 {
@@ -101,7 +141,6 @@ in
         '';
       };
 
-      # TODO: add option to add additional plugins
       extraPluginConfig = mkOption {
         default = "";
         type = types.lines;
@@ -115,6 +154,66 @@ in
         '';
       };
 
+      extraPlugins = mkOption {
+        default = {};
+        type = with types; attrsOf path;
+        description = ''
+          Additional Munin plugins to activate. Keys are the name of the plugin
+          symlink, values are the path to the underlying plugin script. You
+          can use the same plugin script multiple times (e.g. for wildcard
+          plugins).
+
+          Note that these plugins do not participate in autoconfiguration. If
+          you want to autoconfigure additional plugins, use
+          <option>services.munin-node.extraAutoPlugins</option>.
+
+          Plugins enabled in this manner take precedence over autoconfigured
+          plugins.
+
+          Plugins will be copied into the Nix store, and it will attempt to
+          modify them to run properly by fixing hardcoded references to
+          <literal>/bin</literal>, <literal>/usr/bin</literal>,
+          <literal>/sbin</literal>, and <literal>/usr/sbin</literal>.
+        '';
+        example = literalExample ''
+          {
+            zfs_usage_bigpool = /src/munin-contrib/plugins/zfs/zfs_usage_;
+            zfs_usage_smallpool = /src/munin-contrib/plugins/zfs/zfs_usage_;
+            zfs_list = /src/munin-contrib/plugins/zfs/zfs_list;
+          };
+        '';
+      };
+
+      extraAutoPlugins = mkOption {
+        default = [];
+        type = with types; listOf path;
+        description = ''
+          Additional Munin plugins to autoconfigure, using
+          <literal>munin-node-configure --suggest</literal>. These should be
+          the actual paths to the plugin files (or directories containing them),
+          not just their names.
+
+          If you want to manually enable individual plugins instead, use
+          <option>services.munin-node.extraPlugins</option>.
+
+          Note that only plugins that have the 'autoconfig' capability will do
+          anything if listed here, since plugins that cannot autoconfigure
+          won't be automatically enabled by
+          <literal>munin-node-configure</literal>.
+
+          Plugins will be copied into the Nix store, and it will attempt to
+          modify them to run properly by fixing hardcoded references to
+          <literal>/bin</literal>, <literal>/usr/bin</literal>,
+          <literal>/sbin</literal>, and <literal>/usr/sbin</literal>.
+        '';
+        example = literalExample ''
+          [
+            /src/munin-contrib/plugins/zfs
+            /src/munin-contrib/plugins/ssh
+          ];
+        '';
+      };
+
       disabledPlugins = mkOption {
         default = [];
         type = with types; listOf string;
@@ -206,6 +305,13 @@ in
         # Autoconfigure builtin plugins
         ${pkgs.munin}/bin/munin-node-configure --suggest --shell --families contrib,auto,manual --config ${nodeConf} --libdir=${pkgs.munin}/lib/plugins --servicedir=/etc/munin/plugins --sconfdir=${pluginConfDir} 2>/dev/null | ${pkgs.bash}/bin/bash
 
+        # Autoconfigure extra plugins
+        ${pkgs.munin}/bin/munin-node-configure --suggest --shell --families contrib,auto,manual --config ${nodeConf} --libdir=${extraAutoPluginDir} --servicedir=/etc/munin/plugins --sconfdir=${pluginConfDir} 2>/dev/null | ${pkgs.bash}/bin/bash
+
+        ${lib.optionalString (nodeCfg.extraPlugins != {}) ''
+            # Link in manually enabled plugins
+            ln -f -s -t /etc/munin/plugins ${extraPluginDir}/*
+          ''}
 
         ${lib.optionalString (nodeCfg.disabledPlugins != []) ''
             # Disable plugins