Use GET on the container to check if the storage container exists

lib/fluent/plugin/out_azure-storage-append-blob.rb

@@ -150,10 +150,23 @@ def write(chunk)
         end
       end
 
+      def container_exists?(container)
+        begin
+          @bs.get_container_properties(container)
+        rescue Azure::Core::Http::HTTPError => ex
+          if ex.status_code == 404 # container does not exist
+            return false
+          else
+            raise
+          end
+        end
+        return true
+      end
+
       private
 
       def ensure_container
-        unless @bs.list_containers.find { |c| c.name == @azure_container }
+        unless container_exists? @azure_container
           if @auto_create_container
             @bs.create_container(@azure_container)
           else

test/plugin/test_out_azure_storage_append_blob.rb

@@ -1,5 +1,7 @@
 require 'helper'
 require 'fluent/plugin/out_azure-storage-append-blob.rb'
+require 'azure/core/http/http_response'
+require 'azure/core/http/http_error'
 
 include Fluent::Test::Helpers
 
@@ -83,4 +85,53 @@ def create_driver(conf = CONFIG)
       assert_equal slice, Time.now.utc.strftime('log/%Y/%m/%d')
     end
   end
+
+  # This class is used to create an Azure::Core::Http::HTTPError. HTTPError parses
+  # a response object when it is created.
+  class FakeResponse
+    def initialize(status=404)
+      @status = status
+      @body = "body"
+      @headers = {}
+    end
+
+    attr_reader :status
+    attr_reader :body
+    attr_reader :headers
+  end
+
+  # This class is used to test plugin functions which interact with the blob service
+  class FakeBlobService
+    def initialize(status)
+      @response = Azure::Core::Http::HttpResponse.new(FakeResponse.new(status))
+    end
+
+    def get_container_properties(container)
+      unless @response.status_code == 200
+        raise Azure::Core::Http::HTTPError.new(@response)
+      end
+    end
+  end
+
+  sub_test_case 'test container_exists' do
+    test 'container 404 returns false' do
+      d = create_driver
+      d.instance.instance_variable_set(:@bs, FakeBlobService.new(404))
+      assert_false d.instance.container_exists? "anything"
+    end
+
+    test 'existing container returns true' do
+      d = create_driver
+      d.instance.instance_variable_set(:@bs, FakeBlobService.new(200))
+      assert_true d.instance.container_exists? "anything"
+    end
+
+    test 'unexpected exception raises' do
+      d = create_driver
+      d.instance.instance_variable_set(:@bs, FakeBlobService.new(500))
+      assert_raise_kind_of Azure::Core::Http::HTTPError do
+        d.instance.container_exists? "anything"
+      end
+    end
+  end
 end