@@ -690,7 +690,7 @@ namespace :integration do
       project_id = gcloud_project_id
       fail "Unabled to determine project_id from gcloud SDK. Please make " \
         "sure gcloud SDK is logged in and a valid project ID is configured." unless project_id
-      # If project_uri not given, default to "http://[project_id].appspot.com"
+      # If project_uri not given, default to "http://[project_id].appspot-preview.com"
       project_uri = args[:project_uri] ||
                     "http://#{project_id}.appspot-preview.com"
 
@@ -701,7 +701,7 @@ namespace :integration do
 
       test_apps.each do |test_app|
         header "Deploying #{test_app} to GAE Flex"
-        deploy_gae_flex test_app do
+        deploy_gae_flex test_app, project_uri do
           valid_gems.each do |gem|
             Dir.chdir gem do
               header "Running integration:gae for gem #{gem}"
 
@@ -19,7 +19,7 @@
 # Setup the app.yaml file and deploy this directory to GAE. When run from repo
 # root directory, this will deploy the integration/classic_sinatra_app.rb onto
 # GAE for testing use.
-def deploy_gae_flex app_dir
+def deploy_gae_flex app_dir, project_uri
   unless File.file? "app.yaml"
     FileUtils.cp "#{app_dir}/app.yaml.example", "app.yaml"
     temp_app_yaml = true
@@ -31,15 +31,21 @@ def deploy_gae_flex app_dir
     last_gae_version = get_gae_versions.last
     sh "gcloud beta app deploy -q" do |ok, res|
       if ok
-        # Wait couple minutes for load balancer to stablize
-        sleep 120
+        # Make sure the deployment is fully accessible.
+        keep_trying_till_true 300 do
+          verify_uri_acessibility project_uri
+        end
 
         yield
 
         # Delete the last version of Google App Engine if successfully deployed
         unless last_gae_version.empty?
           puts "gcloud app versions delete #{last_gae_version} -q"
-          `gcloud app versions delete #{last_gae_version} -q`
+          keep_trying_till_true 600 do
+            `gcloud app versions delete #{last_gae_version} -q`
+
+            !get_gae_versions.include?(last_gae_version)
+          end
         end
       else
         fail "'gcloud app deploy' failed with status = #{res.exitstatus}"
 
@@ -15,23 +15,33 @@
 
 require "fileutils"
 require "open3"
+require "net/http"
 
 ##
 # Keep trying a block of code until the code of block yield a true statement or
 # raise error after timeout
 def keep_trying_till_true timeout = 30
   t_begin = Time.now
+  delay = 2
   loop do
     if yield
       break
     elsif (Time.now - t_begin) > timeout
       fail "Timeout after trying for #{timeout} seconds"
     else
-      sleep 1
+      sleep delay
     end
+    delay += 1
   end
 end
 
+##
+# Verify the given uri can be accessed successfully.
+def verify_uri_acessibility uri
+  res = Net::HTTP.get_response URI(uri)
+  res.is_a? Net::HTTPSuccess
+end
+
 ##
 # Get GCP project id from Gcloud SDK
 def gcloud_project_id