Added validation to ec2 region names.

An argument error is raised if the region name is an availability
zone. This should eliminate the unhelpful networking errors raised
when failing to resolve the endpoint.

Fixes #966

CHANGELOG.md

@@ -1,6 +1,17 @@
 Unreleased Changes
 ------------------
 
+* Feature - Aws::EC2 - Added helpful error messages when configuring an
+  `Aws::EC2::Client` with region which is actually an availability zone.
+  This will prevent users from getting unhelpful networking errors.
+
+  ```ruby
+  Aws::EC2::Client.new(region: 'us-east-1a')
+  #=> raises ArgumentError: :region should be a region name, not an availability zone name; try `us-west-2' instead of `us-west-2a'
+  ```
+
+  See [related GitHub issue #966](https://github.com/aws/aws-sdk-ruby/issues/966).
+
 * Issue - Aws::InstanceProfileCredentials - Now retries errors
   raised while attempting to parse the expiration time from
   instance metadata credentials.

aws-sdk-core/lib/aws-sdk-core.rb

@@ -146,6 +146,7 @@ module Plugins
     autoload :DynamoDBSimpleAttributes, 'aws-sdk-core/plugins/dynamodb_simple_attributes'
     autoload :DynamoDBCRC32Validation, 'aws-sdk-core/plugins/dynamodb_crc32_validation'
     autoload :EC2CopyEncryptedSnapshot, 'aws-sdk-core/plugins/ec2_copy_encrypted_snapshot'
+    autoload :EC2RegionValidation, 'aws-sdk-core/plugins/ec2_region_validation'
     autoload :GlacierAccountId, 'aws-sdk-core/plugins/glacier_account_id'
     autoload :GlacierApiVersion, 'aws-sdk-core/plugins/glacier_api_version'
     autoload :GlacierChecksums, 'aws-sdk-core/plugins/glacier_checksums'

aws-sdk-core/lib/aws-sdk-core/api/customizations.rb

@@ -80,6 +80,7 @@ def apply_plugins(client_class)
 
       plugins('ec2', add: %w(
         Aws::Plugins::EC2CopyEncryptedSnapshot
+        Aws::Plugins::EC2RegionValidation
       ))
 
       api('glacier') do |api|

aws-sdk-core/lib/aws-sdk-core/plugins/ec2_region_validation.rb

@@ -0,0 +1,17 @@
+module Aws
+  module Plugins
+    # @api private
+    class EC2RegionValidation < Seahorse::Client::Plugin
+
+      def after_initialize(client)
+        if region = client.config.region
+          if matches = region.match(/^(\w+-\w+-\d+)[a-z]$/)
+            msg = ":region option must a region name, not an availability "
+            msg << "zone name; try `#{matches[1]}' instead of `#{matches[0]}'"
+            raise ArgumentError, msg
+          end
+        end
+      end
+    end
+  end
+end

aws-sdk-core/spec/aws/ec2/client_spec.rb

@@ -17,6 +17,16 @@ module EC2
 
       end
 
+      describe ':region' do
+
+        it 'should not be an availability zone' do
+          expect {
+            Client.new(region: 'us-east-1a')
+          }.to raise_error(ArgumentError)
+        end
+
+      end
+
       describe '#copy_snapshot' do
 
         it 'requires a source shapshot region' do