[QENG-4075] Allow specifying 'graphs:' for dashboard

Prior to this the dashboard front-end would use the configuration settings
for `graphite[:server]`/`graphite[:prefix]` to locate a graphite server
to use for rendering graphs.

Now that we have multiple possible metrics backends, the front-end graph
host for the dashboard could be entirely different from the back-end metrics
server that we publish to (if any).

This decouples those settings:

 - use `graphs[:server]` / `graphs[:prefix]` for the graphite-compatible web front-end to use for dashboard display graphs
 - fall back to `graphite[:server]`/`graphite[:prefix]` if `graphs` is not specified, in order to support legacy `vmpooler.yaml` configurations.

Note that since `statsd` takes precedence over `graphite`, it's possible to specify both `statsd` (for publishing) and `graphite` (for reading). We still prefer `graphs` over `graphite`.

Updated the example `vmpooler.yaml` config file.

lib/vmpooler/api/dashboard.rb

@@ -1,9 +1,57 @@
 module Vmpooler
   class API
   class Dashboard < Sinatra::Base
+
+    # handle to the App's configuration information
+    def config
+      @config ||= Vmpooler::API.settings.config
+    end
+
+    # configuration setting for server hosting graph URLs to view
+    def graph_server
+      return @graph_server if @graph_server
+
+      if config[:graphs]
+        return false unless config[:graphs]['server']
+        @graph_server = config[:graphs]['server']
+      elsif config[:graphite]
+        return false unless config[:graphite]['server']
+        @graph_server = config[:graphite]['server']
+      else
+        false
+      end
+    end
+
+    # configuration setting for URL prefix for graphs to view
+    def graph_prefix
+      return @graph_prefix if @graph_prefix
+
+      if config[:graphs]
+        return false unless config[:graphs]['prefix']
+        @graph_prefix = config[:graphs]['prefix']
+      elsif config[:graphite]
+        return false unless config[:graphite]['prefix']
+        @graph_prefix = config[:graphite]['prefix']
+      else
+        false
+      end
+    end
+
+    # what is the base URL for viewable graphs?
+    def graph_url
+      return false unless graph_server && graph_prefix
+      @graph_url ||= "http://#{graph_server}/render?target=#{graph_prefix}"
+    end
+
+    # return a full URL to a viewable graph for a given metrics target (graphite syntax)
+    def graph_link(target = "")
+      return "" unless graph_url
+      graph_url + target
+    end
+
+
     get '/dashboard/stats/vmpooler/pool/?' do
       content_type :json
-
       result = {}
 
       Vmpooler::API.settings.config[:pools].each do |pool|
@@ -13,13 +61,11 @@ module Vmpooler
       end
 
       if params[:history]
-        if Vmpooler::API.settings.config[:graphite]['server']
+        if graph_url
           history ||= {}
 
           begin
-            buffer = open(
+            buffer = open(graph_link('.qready.*&from=-1hour&format=json')).read
-              'http://' + Vmpooler::API.settings.config[:graphite]['server'] + '/render?target=' + Vmpooler::API.settings.config[:graphite]['prefix'] + '.ready.*&from=-1hour&format=json'
-            ).read
             history = JSON.parse(buffer)
 
             history.each do |pool|
@@ -52,59 +98,47 @@ module Vmpooler
           end
         end
       end
-
       JSON.pretty_generate(result)
     end
 
     get '/dashboard/stats/vmpooler/running/?' do
       content_type :json
-
       result = {}
 
       Vmpooler::API.settings.config[:pools].each do |pool|
         running = Vmpooler::API.settings.redis.scard('vmpooler__running__' + pool['name'])
         pool['major'] = Regexp.last_match[1] if pool['name'] =~ /^(\w+)\-/
-
         result[pool['major']] ||= {}
-
         result[pool['major']]['running'] = result[pool['major']]['running'].to_i + running.to_i
       end
 
       if params[:history]
-        if Vmpooler::API.settings.config[:graphite]['server']
+        if graph_url
           begin
-            buffer = open(
+            buffer = open(graph_link('.running.*&from=-1hour&format=json')).read
-              'http://' + Vmpooler::API.settings.config[:graphite]['server'] + '/render?target=' + Vmpooler::API.settings.config[:graphite]['prefix'] + '.running.*&from=-1hour&format=json'
-            ).read
             JSON.parse(buffer).each do |pool|
               if pool['target'] =~ /.*\.(.*)$/
                 pool['name'] = Regexp.last_match[1]
-
                 pool['major'] = Regexp.last_match[1] if pool['name'] =~ /^(\w+)\-/
-
                 result[pool['major']]['history'] ||= Array.new
 
                 for i in 0..pool['datapoints'].length
                   if
                     pool['datapoints'][i] &&
                     pool['datapoints'][i][0]
-
                     pool['last'] = pool['datapoints'][i][0]
-
                     result[pool['major']]['history'][i] ||= 0
                     result[pool['major']]['history'][i] = result[pool['major']]['history'][i].to_i + pool['datapoints'][i][0].to_i
                   else
                     result[pool['major']]['history'][i] = result[pool['major']]['history'][i].to_i + pool['last'].to_i
                   end
                 end
-
               end
             end
           rescue
           end
         end
       end
-
       JSON.pretty_generate(result)
     end
   end

vmpooler.yaml.example

@@ -54,6 +54,32 @@
   server: 'redis.company.com'
 
 
+  # :graphs:
+  #
+  # This section contains the server and prefix information for a graphite-
+  # compatible web front-end where graphs may be viewed. This is used by the
+  # vmpooler dashboard to retrieve statistics and graphs for a given instance.
+  #
+  # NOTE: This is not the endpoint for publishing metrics data. See `graphite:`
+  #       and `statsd:` below.
+  #
+  # NOTE: If `graphs:` is not set, for legacy compatibility, `graphite:` will be
+  #       consulted for `server`/`prefix` information to use in locating a
+  #       graph server for our dashboard.  `graphs:` is recommended over
+  #       `graphite:`
+  #
+  #
+  # Available configuration parameters:
+  #
+  #
+  #   - server
+  #     The FQDN hostname of the statsd daemon.
+  #     (required)
+  #
+  #   - prefix
+  #     The prefix to use while storing statsd data.
+  #     (optional; default: 'vmpooler')
+
   # :statsd:
   #
   # This section contains the connection information required to store