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+---
+layout: default
+title: Aggregate Plugins
+---
+[DDL]: /mcollective/reference/plugins/ddl.html
+[Examples]: https://github.com/puppetlabs/marionette-collective/tree/master/plugins/mcollective/aggregate
+
+## Overview
+MCollective Agents return data and we try to provide as much usable user
+interface for free. To aid in this we require agents to have [DDL] files that
+describe the data that the agent returns.
+
+DDL files are used to configure the client but also to assist with user
+interface generation.  They are used to ask questions that an action needs but
+also to render the results when the replies come in.  For example we turn
+*:freecpu* into "Free CPU" when displaying the data based on the DDL.
+
+Previously if data that agents returned required any summarization this had to
+be done using a custom application.  Here is an example from *mco nrpe*:
+
+{% highlight console %}
+% mco nrpe check_load
+.
+.
+Finished processing 25 / 25 hosts in 556.48 ms
+
+              OK: 25
+         WARNING: 0
+        CRITICAL: 0
+         UNKNOWN: 0
+{% endhighlight %}
+
+Here to get the summary of results displayed in a way that has contextual
+relevance to the nrpe plugin a custom application had to be written and anyone
+who interacts with the agent using other RPC clients would not get the benefit
+of this summary.
+
+By using aggregate plugins and updating the DDL we can now provide such a
+summary in all result sets and display it using the *mco rpc* application and
+any calls to *printrpc*.
+
+{% highlight console %}
+% mco rpc nrpe runcommand command=check_load
+Discovering hosts using the mongo method .... 25
+
+ * [============================================================> ] 25 / 25
+
+Summary of Exit Code:
+
+            OK : 25
+       WARNING : 0
+       UNKNOWN : 0
+      CRITICAL : 0
+
+
+Finished processing 25 / 25 hosts in 390.70 ms
+{% endhighlight %}
+
+Here you get a similar summary as before, all that had to be done was a simple
+aggregate plugin be written and distributed with your clients.
+
+The results are shown as above using *printrpcstats* but you can also get access to
+the raw data so you can decide to render it in some other way - perhaps using a
+graph on a web interface.
+
+We provide a number of aggregate plugins with MCollective and anyone can write
+more.
+
+For examples that already use functions see the *rpcutil* agent - its
+*collective_info*, *get_fact*, *daemon_stats* and *get_config_item* actions all
+have summaries applied.
+
+*NOTE:* This feature is available since version 2.1.0
+
+## Using existing plugins
+
+### Updating the DDL
+At present MCollective supplies 3 plugins *average()*, *summary()* and *sum()*
+you can use these in any agent, here is an example from the *rpcutil* agent DDL
+file:
+
+{% highlight ruby %}
+action "get_config_item", :description => "Get the active value of a specific config property" do
+    output :value,
+           :description => "The value that is in use",
+           :display_as => "Value"
+
+    summarize do
+        aggregate summary(:value)
+    end
+end
+{% endhighlight %}
+
+We've removed a few lines from this example DDL block leaving only the relevant
+lines.  You can see the agent outputs data called *:value* and we reference that
+output in the summary function *summary(:value)*, the result would look like
+this:
+
+### Viewing summaries on the CLI
+{% highlight console %}
+% mco rpc rpcutil get_config_item item=collectives
+.
+.
+dev8
+   Property: collectives
+      Value: ["mcollective", "uk_collective"]
+
+Summary of Value:
+
+      mcollective = 25
+    uk_collective = 15
+    fr_collective = 9
+    us_collective = 1
+
+Finished processing 25 / 25 hosts in 349.70 ms
+{% endhighlight %}
+
+You can see that the value in this case contains arrays, the *summary()*
+function produce the table in the output showing the data distribution.
+
+### Producing summaries in your own clients
+You can enable the same display in your own code, here is ruby code that has the
+same affect as the CLI call above:
+
+{% highlight ruby %}
+require 'mcollective'
+
+include MCollective::RPC
+
+c = rpcclient("rpcutil")
+
+printrpc c.get_config_item(:item => "collectives")
+
+printrpcstats :summarize => true
+{% endhighlight %}
+
+Without passing in the *:summarize => true* you would not see the summaries
+
+### Getting access to the raw summary results
+If you wanted to do something else entirely like produce a graph on a web page
+of the summaries you can get access to the raw data, here's some ruby code to
+show all computed summaries:
+
+{% highlight ruby %}
+require 'mcollective'
+
+include MCollective::RPC
+
+c = rpcclient("rpcutil")
+c.progress = false
+
+c.get_config_item(:item => "collectives")
+
+c.stats.aggregate_summary.each do |summary|
+  puts "Summary of type: %s" % summary.result_type
+  puts "Display format: '%s'" % summary.aggregate_format
+  puts
+  pp summary.result
+end
+{% endhighlight %}
+
+As you can see you will get an array of summaries this is because each DDL can
+use many aggregate calls, this would be an array of all the computed summaries:
+
+{% highlight console %}
+Summary of type: collection
+Display format: '%13s = %s'
+
+{:type=>:collection,
+ :value=>
+  {"mcollective"=>25,
+   "fr_collective"=>9,
+   "us_collective"=>1,
+   "uk_collective"=>15},
+ :output=>:value}
+{% endhighlight %}
+
+There are 2 types of result *:collection* and *:numeric*, in the case of numeric
+results the :value would just be a number.
+
+The *aggregate_format* is either a user supplied format or a dynamically
+computed format to display the summary results on the console.  In this case
+each pair of the hash should be displayed using the format to produce a nice
+right justified list of keys and values.
+
+## Writing your own function
+We'll cover writing your own function by looking at the Nagios one from earlier
+in this example.  You can look at [the functions supplied with
+MCollective][Examples] for more examples using other types than the one below.
+
+First lets look at the DDL for the existing *nrpe* Agent:
+
+{% highlight ruby %}
+action "runcommand", :description => "Run a NRPE command" do
+    input :command,
+          :prompt      => "Command",
+          :description => "NRPE command to run",
+          :type        => :string,
+          :validation  => '\A[a-zA-Z0-9_-]+\z',
+          :optional    => false,
+          :maxlength   => 50
+
+    output :output,
+           :description => "Output from the Nagios plugin",
+           :display_as  => "Output",
+           :default     => ""
+
+    output :exitcode,
+           :description  => "Exit Code from the Nagios plugin",
+           :display_as   => "Exit Code",
+           :default      => 3
+
+    output :perfdata,
+           :description  => "Performance Data from the Nagios plugin",
+           :display_as   => "Performance Data",
+           :default      => ""
+end
+{% endhighlight %}
+
+You can see it will return an *:exitcode* item and from the default value you
+can gather this is going to be a number.  Nagios defines 4 possibly exit codes
+for a Nagios plugin and we need to convert this *:exitcode* into a string like
+WARNING, CRITICAL, UNKNOWN or OK.
+
+Usually when writing any kind of summarizer for an array of results your code
+might contain 3 phases.
+
+Given a series of Nagios results like this:
+
+{% highlight ruby %}
+[
+ {:exitcode => 0, :output => "OK", :perfdata => ""},
+ {:exitcode => 2, :output => "failure", :perfdata => ""}
+]
+{% endhighlight %}
+
+You would write a nagios_states() function that does roughly this:
+
+{% highlight ruby %}
+def nagios_states(results)
+  # set initial values
+  result = {}
+  status_map = ["OK", "WARNING", "CRITICAL", "UNKNOWN"]
+  status_map.each {|s| result[s] = 0}
+
+  # loop over all the data, increment the count for OK etc
+  results.each do |result|
+    status = status_map[result[:exitcode]]
+    result[status] += 1
+  end
+
+  # return the result hash, {"OK" => 1, "CRITICAL" => 1, "WARN" => 0, "UNKNOWN" => 0}
+  return result
+end
+{% endhighlight %}
+
+You could optimise the code but you can see there are 3 major stages in the life
+of this code.
+
+ * Set initial values for the return data
+ * Loop the data building up the state
+ * Return the data.
+
+Given this, here is our Nagios exitcode summary function, it is roughly the same
+code with a bit more boiler plate to plugin into mcollective, but the same code
+can be seen:
+
+{% highlight ruby %}
+module MCollective
+  class Aggregate
+    class Nagios_states<Base
+      # Before function is run processing
+      def startup_hook
+        # :collection or :numeric
+        @result[:type] = :collection
+
+        # set default aggregate_format if it is undefined
+        @aggregate_format = "%10s : %s" unless @aggregate_format
+
+        @result[:value] = {}
+
+        @status_map = ["OK", "WARNING", "CRITICAL", "UNKNOWN"]
+        @status_map.each {|s| @result[:value][s] = 0}
+
+      end
+
+      # Determines the average of a set of numerical values
+      def process_result(value, reply)
+        if value
+          status = @status_map[value]
+          @result[:value][status] += 1
+        else
+          @result["UNKNOWN"] += 1
+        end
+      end
+
+      # Post processing hook that returns the summary result
+      def summarize
+        result_class(@result[:type]).new(@result, @aggregate_format, @action)
+      end
+    end
+  end
+end
+{% endhighlight %}
+
+This shows that an aggregate function has the same 3 basic parts.  First we set
+the initial state using the *startup_hook*.  We then process each result as it
+comes in from the network using *process_result*.  Finally we turn that into a
+the result objects that you saw earlier in the ruby client examples using the
+*summarize* method.
+
+### *startup_hook*
+Each function needs a startup hook, without one you'll get exceptions.  The
+startup hook lets you set up the initial state.
+
+The first thing to do is set the type of result this will be.  Currently we
+support 2 types of result either a plain number indicated using *:numeric* or a
+complex *:collection* type that can be a hash with keys and values.
+
+Functions can take display formats in the DDL, in this example we set
+*@aggregate_format* to a *printf* default that would display a table of results
+but we still let the user supply his own format.
+
+We then just initialize the result hash to and build a map from the English
+representation of the Nagios status codes.
+
+### *process_result*
+Every reply that comes in from the network gets passed into your
+*process_result* method.  The first argument will be just the single value the
+DDL indicates you are interested in but you'll also get the whole rely so you
+can get access to other reply values and such.
+
+This gets called each time, we just look at the value and increment each Nagios
+status or treat it as an unknown - in case the result data is missformed.
+
+### *summarize*
+The summarize method lets you take the state you built up and convert that into
+an answer.  The summarize method is optional what you see here is the default
+action if you do not supply one.
+
+The *result_class* method accepts either *:collection* or *:numeric* as
+arguments and it is basically a factory for the correct result structure.
+
+### Deploy and update the DDL
+You should deploy this function into your *libdir/aggregate* directory called
+*nagios_states.rb* on the client machines - no harm deploying it everywhere
+though.
+
+Update the DDL so it looks like:
+
+{% highlight ruby %}
+action "runcommand", :description => "Run a NRPE command" do
+    .
+    .
+    .
+
+    if respond_to?(:summarize)
+        summarize do
+            aggregate nagios_states(:exitcode)
+        end
+    end
+end
+{% endhighlight %}
+
+Add the last few lines - we check that we're running in a version of MCollective
+that supports this feature and then we call our function with the *:exitcode*
+results.
+
+