In some of my recent posts I explained how to install and start
AppScale. I showed how to use AppScale command-line tools to manage an AppScale PaaS on virtualized environments such as
Xen and IaaS environments such as
EC2 and
Eucalyptus. Then we also looked at how to deploy
Google App Engine (GAE) apps over AppScale. In this post we are going to try something different.
Here I’m going to describe a possible hybrid architecture for deploying RESTful services in the cloud and exposing those services through an on-premise API management platform. This type of an architecture is most suitable for B2B integration scenarios where one organization provides a range of services and several other organizations consume them with their own custom use cases and SLAs. Both service providers and service consumers can greatly benefit from the proposed hybrid architecture. It enables the API providers to reap the benefits of the cloud with reduced deployment cost, reduced long-term maintenance overhead and reduced time-to-market. API consumers can use their own on-premise API management platform as a local proxy, which provides powerful access control, rate control, analytics and community features on top of the services already deployed in the cloud.
To try this out, first spin up an AppScale PaaS in a desired cloud environment. You can refer my previous posts or go through the AppScale wiki to learn how to do this. Then we can deploy a simple RESTful web service in our AppScale cloud. Here I’m posting the source code for a simple web service called “starbucks” written in Python using the GAE APIs. The “starbucks” service can be used to submit and manage simple drink orders. It uses the GAE
datastore API to store all the application data and exposes all the fundamental CRUD operations as REST calls (Creare = POST, Update = PUT, Read = GET, Delete = DELETE).
try:
import json
except ImportError:
import simplejson as json
import random
import uuid
from google.appengine.ext import db, webapp
from google.appengine.ext.webapp.util import run_wsgi_app
PRICE_CHART = {}
class Order(db.Model):
order_id = db.StringProperty(required=True)
drink = db.StringProperty(required=True)
additions = db.StringListProperty()
cost = db.FloatProperty()
def get_price(order):
if PRICE_CHART.has_key(order.drink):
price = PRICE_CHART[order.drink]
else:
price = random.randint(2, 6) - 0.01
PRICE_CHART[order.drink] = price
if order.additions is not None:
price += 0.50 * len(order.additions)
return price
def send_json_response(response, payload, status=200):
response.headers['Content-Type'] = 'application/json'
response.set_status(status)
if isinstance(payload, Order):
payload = {
'id' : payload.order_id,
'drink' : payload.drink,
'cost' : payload.cost,
'additions' : payload.additions
}
response.out.write(json.dumps(payload))
class OrderSubmissionHandler(webapp.RequestHandler):
def post(self):
order_info = json.loads(self.request.body)
order_id = str(uuid.uuid1())
drink = order_info['drink']
order = Order(order_id=order_id, drink=drink, key_name=order_id)
if order_info.has_key('additions'):
additions = order_info['additions']
if isinstance(additions, list):
order.additions = additions
else:
order.additions = [ additions ]
else:
order.additions = []
order.cost = get_price(order)
order.put()
self.response.headers['Location'] = self.request.url + '/' + order_id
send_json_response(self.response, order, 201)
class OrderManagementHandler(webapp.RequestHandler):
def get(self, order_id):
order = Order.get_by_key_name(order_id)
if order is not None:
send_json_response(self.response, order)
else:
self.send_order_not_found(order_id)
def put(self, order_id):
order = Order.get_by_key_name(order_id)
if order is not None:
order_info = json.loads(self.request.body)
drink = order_info['drink']
order.drink = drink
if order_info.has_key('additions'):
additions = order_info['additions']
if isinstance(additions, list):
order.additions = additions
else:
order.additions = [ additions ]
else:
order.additions = []
order.cost = get_price(order)
order.put()
send_json_response(self.response, order)
else:
self.send_order_not_found(order_id)
def delete(self, order_id):
order = Order.get_by_key_name(order_id)
if order is not None:
order.delete()
send_json_response(self.response, order)
else:
self.send_order_not_found(order_id)
def send_order_not_found(self, order_id):
info = {
'error' : 'Not Found',
'message' : 'No order exists by the ID: %s' % order_id,
}
send_json_response(self.response, info, 404)
app = webapp.WSGIApplication([
('/order', OrderSubmissionHandler),
('/order/(.*)', OrderManagementHandler)
], debug=True)
if __name__ == '__main__':
run_wsgi_app(app)
Before we go any further let’s take a few seconds and appreciate how simple and concise this piece of code is. With just about 100 lines of Python code we have developed a comprehensive webapp, which uses JSON as the data exchange format and also does database access and provides decent error handling. Imagine doing the same thing in a language like Java in a traditional servlet container environment. We will have to write lot more code and also bundle a ridiculous amount of additional dependencies to parse and construct JSON and perform database queries. But as seen here, GAE APIs make it absolutely trivial to develop powerful web APIs for the cloud with a minimum amount of code.
You can download the complete “starbucks” application from
here. Simply extract the downloaded tar ball and you’re good to go. The webapp consists of just 2 files. The main.py contains all the source code of the app and app.yaml is the GAE webpp descriptor. No additional libraries or files are needed to make this work. Use AppScale-Tools to deploy the app in your AppScale cloud.
appscale-upload-app –-file /path/to/starbucks --keyname my_key_name
To try out the app, put the following JSON string into a file named order.json:
{
"drink" : "Caramel Frapaccino",
"additions" : [ "Whip Cream" ]
}
Now execute the following Curl request on your App:
curl –v –d @order.json –H “Content-type: application/json” http://host:port/order
Replace 'host'
and 'port' with the appropriate values for your AppScale PaaS. This request should return a HTTP 201 Created response with a Location header.
And now for the API management part. For this I’m going to use the open source API management solution from WSO2, a project that I was a part of a while ago. Download the latest
WSO2 API Manager and install it on your local computer by extracting the zip archive. Go into the bin directory and execute wso2server.sh (or wso2server.bat for Windows) to start the API Manager. You need to have JDK 1.6 or higher installed to be able to do this.
Once the server is up and running, navigate to http://localhost:9763/publisher and sign in to the console using “admin” as both the username and the password. Go ahead and create an API for our “starbucks” service in the cloud. You can use http://host
:port as the service URL where 'host' and 'port' should point to the AppScale PaaS. API creation process should be pretty straightforward. If you need any help, you can refer my past blog posts on WSO2 API Manager or go through the WSO2 documentation. Once the API is created and published, head over to the API Store at http://localhost:9763/store.
Now you can sign up at the API Store as an API consumer, generate an API key for the Starbucks API and start using it.
curl –v –d @order.json –H “Content-type: application/json” –H “Authorization: Bearer api_key” http://localhost:8280/starbucks/1.0.0/order
Review Order:
curl –v –H “Authorization: Bearer api_key” http://localhost:8280/starbucks/1.0.0/order/order_id
Delete Order:
curl –v –X DELETE –H “Authorization: Bearer api_key” http://localhost:8280/starbucks/1.0.0/order/order_id
Replace 'api_key' with the API key generated by the API Store. Replace the 'order_id' with the unique identifier sent in the response for the submit order request.
There you have it. On-premise API management for services in the cloud. This looks pretty simple at first glimpse, but actually this is a quite powerful architecture. Note that all the critical components (service runtime, registry and consumer) are very well separated from each other, which allows maximum flexibility. The portions in the cloud can benefit from cloud specific features such as autoscaling to deliver the maximum throughput with optimal resource utilization. Since the API management platform is being controlled by individual consumer organizations, they can easily enforce their own custom policies, SLAs and optimize for their common access patterns.
