Add website healthcheck example

Fixes #18

Author: andrewvc

examples/website_availability.conf

@@ -0,0 +1,93 @@
+input {
+  http_poller {
+    urls => {
+      "localhost" => "http://localhost:8000"
+    }
+    automatic_retries => 0
+    # Check the site every 10s
+    interval => 10
+    # Wait no longer than 4 seconds for the request to complete
+    request_timeout => 8
+    # Store metadata about the request in this field
+    metadata_target => http_poller_metadata
+    # Tag this request so that we can throttle it in a filter
+    tags => website_healthcheck
+  }
+}
+
+filter {
+  # The poller doesn't set an '@host' field because it may or may not have meaning
+  # In this case we can set it to the 'name' of the host which will be 'localhost'
+  # The name is the key used in the poller's 'url' config
+  if [http_poller_metadata] {
+    mutate {
+      add_field => {
+        "@host" => "%{http_poller_metadata[name]}"
+      }
+    }
+  }
+
+  # Classify slow requests
+  if [http_poller_metadata][runtime_seconds] and [http_poller_metadata][runtime_seconds] > 0.5 {
+    mutate {
+      add_tag => "slow_request"
+    }
+  }
+
+  # Classify requests that can't connect or have an unexpected response code
+  if [http_request_failure] or
+     [http_poller_metadata][code] != 200 {
+
+     # Tag all these events as being bad
+     mutate {
+       add_tag => "bad_request"
+     }
+ }
+
+ if "bad_request" in [tags] {
+    # Tag all but the first message every 10m as "_throttled_poller_alert"
+    # We will later drop messages tagged as such.
+    throttle {
+      key => "%{@host}-RequestFailure"
+      period => 600
+      before_count => -1
+      after_count => 1
+      add_tag => "throttled_poller_alert"
+    }
+
+    # Drop all throttled events
+    if "throttled_poller_alert" in [tags] {
+      drop {}
+    }
+
+    # The SNS output plugin requires special fields to send its messages
+    # This should be fixed soon, but for now we need to set them here
+    mutate {
+      add_field => {
+        sns_subject => "%{@host} is not so healthy! %{@tags}"
+        sns_message => '%{http_request_failure}'
+        codec => json
+
+      }
+    }
+  }
+}
+
+output {
+  # Catch throttled messages for request failures
+  # If we hit one of these, send the output to stdout
+  # as well as an AWS SNS Topic
+  if "http_request_failure" in [tags] {
+    sns {
+      codec => json
+      access_key_id => "AKIAI7T2WMT5ARV3EBNA"
+      secret_access_key => "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"
+      arn => "arn:aws:sns:us-east-1:773216979769:logstash-test-topic"
+    }
+  }
+
+
+  stdout {
+    codec => rubydebug
+  }
+}