[powerdns_recursor] restrict metrics collection

This check now only collects metrics deemed useful.
It also sends a service check.

The configuration file is cleaned, and a few comments are added for
documentation purposes.

checks.d/powerdns_recursor.py

@@ -0,0 +1,77 @@
+# stdlib
+from collections import namedtuple
+
+# Datadog
+from checks import AgentCheck
+
+# 3p
+import requests
+
+
+class PowerDNSRecursorCheck(AgentCheck):
+    # See https://doc.powerdns.com/md/recursor/stats/ for metrics explanation
+    GAUGE_METRICS = [
+        'cache-entries',
+        'concurrent-queries',
+    ]
+    RATE_METRICS = [
+        'all-outqueries',
+        'answers-slow',
+        'answers0-1',
+        'answers1-10',
+        'answers10-100',
+        'answers100-1000',
+        'cache-hits',
+        'cache-misses',
+        'noerror-answers',
+        'outgoing-timeouts',
+        'questions',
+        'servfail-answers',
+        'tcp-outqueries',
+        'tcp-questions',
+    ]
+
+    SERVICE_CHECK_NAME = 'powerdns.recursor.can_connect'
+
+    def check(self, instance):
+        config, tags = self._get_config(instance)
+        stats = self._get_pdns_stats(config)
+        for stat in stats:
+            if stat['name'] in PowerDNSRecursorCheck.GAUGE_METRICS:
+                self.gauge('powerdns.recursor.{}'.format(stat['name']), float(stat['value']), tags=tags)
+            elif stat['name'] in PowerDNSRecursorCheck.RATE_METRICS:
+                self.rate('powerdns.recursor.{}'.format(stat['name']), float(stat['value']), tags=tags)
+
+    def _get_config(self, instance):
+        required = ['host', 'port', 'api_key']
+        for param in required:
+            if not instance.get(param):
+                raise Exception("powerdns_recursor instance missing %s. Skipping." % (param))
+
+        host = instance.get('host')
+        port = int(instance.get('port'))
+        api_key = instance.get('api_key')
+        tags = instance.get('tags', [])
+
+        Config = namedtuple('Config', [
+            'host',
+            'port',
+            'api_key']
+        )
+
+        return Config(host, port, api_key), tags
+
+    def _get_pdns_stats(self, config):
+        url = "http://{}:{}/servers/localhost/statistics".format(config.host, config.port)
+        service_check_tags = ['recursor_host:{}'.format(config.host), 'recursor_port:{}'.format(config.port)]
+        headers = {"X-API-Key": config.api_key}
+        try:
+            request = requests.get(url, headers=headers)
+            request.raise_for_status()
+        except Exception:
+            self.service_check(self.SERVICE_CHECK_NAME, AgentCheck.CRITICAL,
+                               tags=service_check_tags)
+            raise
+        self.service_check(self.SERVICE_CHECK_NAME, AgentCheck.OK,
+                           tags=service_check_tags)
+        return request.json()

conf.d/powerdns-recursor.yaml.example

@@ -0,0 +1,24 @@
+init_config:
+
+instances:
+  # The PowerDNS Recursor check retrieves metrics from the Recursor experimental
+  # web server.
+  # See https://doc.powerdns.com/3/recursor/settings/#experimental-webserver
+  # The API key has to be set as well:
+  # https://doc.powerdns.com/3/recursor/settings/#experimental-api-key
+  #
+  # This check works with PowerDNS Recursor 3.x.
+
+
+
+  # Host running the recursor.
+  - host: 127.0.0.1
+  # Recursor web server port.
+    port: 8082
+  # Recursor web server api key.
+    api_key: pdns_api_key
+
+  # Optional tags to be applied to every emitted metric.
+    # tags:
+    #   - key:value
+    #   - instance:production