# Extract region from instance metadata instead of parsing availability zone

Extract region from instance metadata instead of parsing availability zone and updated tests accordingly

# Why is this change needed?
Information about region is available from instance metadata. Use it instead of unreliable availability zone name parsing

# How does it address the issue?
Extract region from instance metadata

# How was this tested ?
```
bb release
```

cr https://code.amazon.com/reviews/CR-17976878

Author: Alena Kastsiukavets

lib/instance_metadata.rb

@@ -2,14 +2,14 @@
 require 'json'
 require 'instance_agent'
 
+# https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/instance-identity-documents.html
 class InstanceMetadata
 
   IP_ADDRESS = '169.254.169.254'
   PORT = 80
   HTTP_TIMEOUT = 30
-  
+
   def self.host_identifier
-    doc = JSON.parse(http_get('/latest/dynamic/instance-identity/document').strip)
     "arn:#{partition}:ec2:#{doc['region']}:#{doc['accountId']}:instance/#{doc['instanceId']}"
   end
 
@@ -18,15 +18,7 @@ def self.partition
   end
 
   def self.region
-    begin 
-      az = http_get('/latest/meta-data/placement/availability-zone').strip
-    rescue Net::ReadTimeout, Net::OpenTimeout
-      raise InstanceMetadata::InstanceMetadataError.new('Not an EC2 instance and region not provided in the environment variable AWS_REGION. Please specify your region using environment variable AWS_REGION.')
-    end
-
-    raise "Invalid availability zone name: #{az}" unless
-      az =~ /[a-z]{2}-[a-z]+-\d+[a-z]/
-    az.chop
+    doc['region']
   end
 
   def self.instance_id
@@ -57,4 +49,9 @@ def self.http_get(path)
       return response.body
     end
   end
+
+  private
+  def self.doc
+    JSON.parse(http_get('/latest/dynamic/instance-identity/document').strip)
+  end
 end

test/instance_metadata_test.rb

@@ -5,7 +5,6 @@ class InstanceMetadataTest < InstanceAgentTestCase
 
   def self.should_check_status_code(&blk)
     should 'raise unless status code is 200' do
-      @response.stubs(:code).returns(503)
       @instance_doc_response.stubs(:code).returns(503)
       assert_raise(&blk)
     end
@@ -20,23 +19,19 @@ def self.should_check_status_code(&blk)
       @host_identifier = "arn:#{@partition}:ec2:#{region}:#{account_id}:instance/#{instance_id}"
       @instance_document = JSON.dump({"accountId" => account_id, "region" => region, "instanceId" => instance_id})
       @http = mock()
-      @response = mock()
       @instance_doc_response = mock()
       @partition_response = mock()
       @partition_response.stubs(:code).returns("200")
-      @response.stubs(:code).returns("200")
       @instance_doc_response.stubs(:code).returns("200")
 
       @http.stubs(:get).with('/latest/meta-data/services/partition').returns(@partition_response)
-      @http.stubs(:get).with('/latest/meta-data/placement/availability-zone').returns(@response)
       @http.stubs(:get).with('/latest/dynamic/instance-identity/document').returns(@instance_doc_response)
       Net::HTTP.stubs(:start).yields(@http)
     end
 
     context 'getting the host identifier' do
 
       setup do
-        @response.stubs(:body).returns("us-east-1a")
         @partition_response.stubs(:body).returns(@partition)
         @instance_doc_response.stubs(:body).returns(@instance_document)
       end
@@ -69,7 +64,7 @@ def self.should_check_status_code(&blk)
     context 'getting the region' do
 
       setup do
-        @response.stubs(:body).returns("us-east-1a")
+        @instance_doc_response.stubs(:body).returns(@instance_document)
       end
 
       should 'connect to the right host' do
@@ -79,41 +74,12 @@ def self.should_check_status_code(&blk)
 
       should 'call the correct URL' do
         @http.expects(:get).
-          with("/latest/meta-data/placement/availability-zone").
-          returns(@response)
+          with("/latest/dynamic/instance-identity/document").
+          returns(@instance_doc_response)
         InstanceMetadata.region
       end
 
       should 'return the region part of the AZ' do
-        @response.stubs(:body).returns("us-east-1a")
-        assert_equal("us-east-1", InstanceMetadata.region)
-      end
-
-      should 'raise InstanceMetadataError if http read times out' do
-        @http.expects(:get).
-          with("/latest/meta-data/placement/availability-zone").
-          raises(Net::ReadTimeout)
-        assert_raised_with_message('Not an EC2 instance and region not provided in the environment variable AWS_REGION. Please specify your region using environment variable AWS_REGION.', InstanceMetadata::InstanceMetadataError) do
-          InstanceMetadata.region
-        end
-      end
-
-      should 'raise InstanceMetadataError if http open times out' do
-        @http.expects(:get).
-          with("/latest/meta-data/placement/availability-zone").
-          raises(Net::OpenTimeout)
-        assert_raised_with_message('Not an EC2 instance and region not provided in the environment variable AWS_REGION. Please specify your region using environment variable AWS_REGION.', InstanceMetadata::InstanceMetadataError) do
-          InstanceMetadata.region
-        end
-      end
-
-      should 'raise an error if the response is not an AZ' do
-        @response.stubs(:body).returns("foobar")
-        assert_raise { InstanceMetadata.region }
-      end
-
-      should 'ignore whitespace in the body' do
-        @response.stubs(:body).returns(" \tus-east-1a   ")
         assert_equal("us-east-1", InstanceMetadata.region)
       end