ec2_metadata.rb in ohai-6.18.0.rc.0

- old
+ new

@@ -20,15 +20,32 @@
 require 'net/http'
 require 'socket'
 
 module Ohai
   module Mixin
+    ##
+    # This code parses the EC2 Instance Metadata API to provide details
+    # of the running instance.
+    #
+    # Earlier version of this code assumed a specific version of the
+    # metadata API was available. Unfortunately the API versions
+    # supported by a particular instance are determined at instance
+    # launch and are not extended over the life of the instance. As such
+    # the earlier code would fail depending on the age of the instance.
+    #
+    # The updated code probes the instance metadata endpoint for
+    # available versions, determines the most advanced version known to
+    # work and executes the metadata retrieval using that version.
+    #
+    # If no compatible version is found, an empty hash is returned.
+    #
     module Ec2Metadata
 
       EC2_METADATA_ADDR = "169.254.169.254" unless defined?(EC2_METADATA_ADDR)
-      EC2_METADATA_URL = "/2012-01-12/meta-data" unless defined?(EC2_METADATA_URL)
-      EC2_USERDATA_URL = "/2012-01-12/user-data" unless defined?(EC2_USERDATA_URL)
+      EC2_SUPPORTED_VERSIONS = %w[ 1.0 2007-01-19 2007-03-01 2007-08-29 2007-10-10 2007-12-15
+                                   2008-02-01 2008-09-01 2009-04-04 2011-01-01 2011-05-01 2012-01-12 ]
+
       EC2_ARRAY_VALUES = %w(security-groups)
       EC2_ARRAY_DIR    = %w(network/interfaces/macs)
       EC2_JSON_DIR     = %w(iam)
 
       def can_metadata_connect?(addr, port, timeout=2)
@@ -55,71 +72,103 @@
         end
         Ohai::Log.debug("can_metadata_connect? == #{connected}")
         connected
       end
 
+      def best_api_version
+        response = http_client.get("/")
+        unless response.code == '200'
+          raise "Unable to determine EC2 metadata version (returned #{response.code} response)"
+        end
+        # Note: Sorting the list of versions may have unintended consequences in
+        # non-EC2 environments. It appears to be safe in EC2 as of 2013-04-12.
+        versions = response.body.split("\n")
+        versions = response.body.split("\n").sort
+        until (versions.empty? || EC2_SUPPORTED_VERSIONS.include?(versions.last)) do
+          pv = versions.pop
+          Ohai::Log.debug("EC2 shows unsupported metadata version: #{pv}") unless pv == 'latest'
+        end
+        Ohai::Log.debug("EC2 metadata version: #{versions.last}")
+        if versions.empty?
+          raise "Unable to determine EC2 metadata version (no supported entries found)"
+        end
+        versions.last
+      end
+
       def http_client
         Net::HTTP.start(EC2_METADATA_ADDR).tap {|h| h.read_timeout = 600}
       end
 
-      def fetch_metadata(id='')
+      def metadata_get(id, api_version)
+        response = http_client.get("/#{api_version}/meta-data/#{id}")
+        unless response.code == '200'
+          raise "Encountered error retrieving EC2 metadata (returned #{response.code} response)"
+        end
+        response
+      end
+
+      def fetch_metadata(id='', api_version=nil)
+        api_version ||= best_api_version
+        return Hash.new if api_version.nil?
         metadata = Hash.new
-        http_client.get("#{EC2_METADATA_URL}/#{id}").body.split("\n").each do |o|
+        metadata_get(id, api_version).body.split("\n").each do |o|
           key = expand_path("#{id}#{o}")
           if key[-1..-1] != '/'
             metadata[metadata_key(key)] =
               if EC2_ARRAY_VALUES.include? key
-                http_client.get("#{EC2_METADATA_URL}/#{key}").body.split("\n")
+                metadata_get(key, api_version).body.split("\n")
               else
-                http_client.get("#{EC2_METADATA_URL}/#{key}").body
+                metadata_get(key, api_version).body
               end
           elsif not key.eql?(id) and not key.eql?('/')
             name = key[0..-2]
-	    sym = metadata_key(name)
+            sym = metadata_key(name)
             if EC2_ARRAY_DIR.include?(name)
-              metadata[sym] = fetch_dir_metadata(key)
+              metadata[sym] = fetch_dir_metadata(key, api_version)
             elsif EC2_JSON_DIR.include?(name)
-              metadata[sym] = fetch_json_dir_metadata(key)
+              metadata[sym] = fetch_json_dir_metadata(key, api_version)
             else
-              fetch_metadata(key).each{|k,v| metadata[k] = v}
+              fetch_metadata(key, api_version).each{|k,v| metadata[k] = v}
             end
           end
         end
         metadata
       end
 
-      def fetch_dir_metadata(id)
+      def fetch_dir_metadata(id, api_version)
         metadata = Hash.new
-        http_client.get("#{EC2_METADATA_URL}/#{id}").body.split("\n").each do |o|
+          metadata_get(id, api_version).body.split("\n").each do |o|
           key = expand_path(o)
           if key[-1..-1] != '/'
-            metadata[metadata_key(key)] = http_client.get("#{EC2_METADATA_URL}/#{id}#{key}").body
+            metadata[metadata_key(key)] = metadata_get("#{id}#{key}", api_version).body
           elsif not key.eql?('/')
-            metadata[key[0..-2]] = fetch_dir_metadata("#{id}#{key}")
+            metadata[key[0..-2]] = fetch_dir_metadata("#{id}#{key}", api_version)
           end
         end
         metadata
       end
 
-      def fetch_json_dir_metadata(id)
+      def fetch_json_dir_metadata(id, api_version)
         metadata = Hash.new
-        http_client.get("#{EC2_METADATA_URL}/#{id}").body.split("\n").each do |o|
+        metadata_get(id, api_version).body.split("\n").each do |o|
           key = expand_path(o)
           if key[-1..-1] != '/'
-            data = http_client.get("#{EC2_METADATA_URL}/#{id}#{key}").body
+            data = metadata_get("#{id}#{key}", api_version).body
             json = StringIO.new(data)
             parser = Yajl::Parser.new
             metadata[metadata_key(key)] = parser.parse(json)
           elsif not key.eql?('/')
-            metadata[key[0..-2]] = fetch_json_dir_metadata("#{id}#{key}")
+            metadata[key[0..-2]] = fetch_json_dir_metadata("#{id}#{key}", api_version)
           end
         end
         metadata
       end
 
       def fetch_userdata()
-        response = http_client.get("#{EC2_USERDATA_URL}/")
+        api_version = best_api_version
+        return nil if api_version.nil?
+        response = http_client.get("/#{api_version}/user-data/")
         response.code == "200" ? response.body : nil
       end
 
       private
 
@@ -136,6 +185,5 @@
       end
 
     end
   end
 end
-