nixos/curator: init elasticsearch curator

https://www.elastic.co/guide/en/elasticsearch/client/curator/5.5/index.html

nixos/modules/services/search/elasticsearch-curator.nix

@@ -0,0 +1,94 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+    cfg = config.services.elasticsearch-curator;
+    curatorConfig = pkgs.writeTextFile {
+      name = "config.yaml";
+      text = ''
+        ---
+        # Remember, leave a key empty if there is no value.  None will be a string,
+        # not a Python "NoneType"
+        client:
+          hosts: ${builtins.toJSON cfg.hosts}
+          port: ${cfg.port}
+          url_prefix:
+          use_ssl: False
+          certificate:
+          client_cert:
+          client_key:
+          ssl_no_validate: False
+          http_auth:
+          timeout: 30
+          master_only: False
+        logging:
+          loglevel: INFO
+          logfile:
+          logformat: default
+          blacklist: ['elasticsearch', 'urllib3']
+        '';
+    };
+    curatorAction = pkgs.writeTextFile {
+      name = "action.yaml";
+      text = cfg.actionYAML;
+    };
+in {
+
+  options.services.elasticsearch-curator = {
+
+    enable = mkEnableOption "elasticsearch curator";
+    interval = mkOption {
+      description = "The frequency to run curator, a systemd.time such as 'hourly'";
+      default = "hourly";
+      type = types.str;
+    };
+    hosts = mkOption {
+      description = "a list of elasticsearch hosts to connect to";
+      type = types.listOf types.str;
+      default = ["localhost"];
+    };
+    port = mkOption {
+      description = "the port that elasticsearch is listening on";
+      type = types.int;
+      default = 9200;
+    };
+    actionYAML = mkOption {
+      description = "curator action.yaml file contents, alternatively use curator-cli which takes a simple action command";
+      example = ''
+        ---
+        actions:
+          1:
+            action: delete_indices
+            description: >-
+              Delete indices older than 45 days (based on index name), for logstash-
+              prefixed indices. Ignore the error if the filter does not result in an
+              actionable list of indices (ignore_empty_list) and exit cleanly.
+            options:
+              ignore_empty_list: True
+              disable_action: False
+            filters:
+            - filtertype: pattern
+              kind: prefix
+              value: logstash-
+            - filtertype: age
+              source: name
+              direction: older
+              timestring: '%Y.%m.%d'
+              unit: days
+              unit_count: 45
+      '';
+    };
+  };
+
+  config = mkIf cfg.enable {
+
+    systemd.services.elasticsearch-curator = {
+      enable = cfg.enable;
+      startAt = cfg.interval;
+      serviceConfig = {
+        ExecStart = ''${pkgs.python36Packages.elasticsearch-curator}/bin/curator --config ${curatorConfig} ${curatorAction}'';
+      };
+    };
+  };
+}