Wednesday, July 2, 2014

Nice Cloud, no rain: Using Cloudant/couchDB with Python on Bluemix

My last two blog entries were about getting started with Python on IBM Bluemix and how to use a custom domain with my Bluemix weather application. Today I am going to show how I added Cloudant and couchDB to my application, both locally and on Bluemix.

Storing the weather data locally doesn't make sense because I can query much more historical data on OpenWeatherMap. So I am going to use a database to log information about for which city and when the data was requested. That information, in aggregated form, could then be reported as fun fact to each user of the app. I chose Cloudant because it is simple to use, adequate for the intended purpose, has free usage plans on Bluemix, and I can use it and test locally as couchDB.

Add Cloudant as new service
The code itself is relatively simple and I put comments (shown at the end of the article). The interesting part is how to add a Cloudant service to my application on Bluemix, how to bind them in the application, and the preparation work for the database itself. So let's take a look at those steps.

Cloudant is offered as one of several services in the "Data Management" category on Bluemix. While on the Dashboard you simply click on the "Add a service" button as show on the right. Navigate to the Data Management section and choose Cloudant.

It will bring up a screen showing information about the service itself, on usage terms, and on the right side of it a dialog "Add Service" for adding the service to your account. Here you can already bind the new database service to your application by selecting an existing application from a dropdown list. I did that and gave my new Cloudant service the name "cloudantWeather" as shown:
Bind Cloudant to
your application
Once the service is added you can bring up the Cloudant administration interface. I have used Cloudant and couchDB before, so that isn't anything new. To avoid dealing with creation of a database as part of the actual program I decided to create a "weather" database through the administration interface for the hosted Cloudant and my local couchDB servers. An interesting but not too tricky part is how to access both servers depending on where the application is running. Information with the username, password, server address and other details is provided in an environment variable VCAP_SERVICES when run on Bluemix. Thus, in the program I am testing for the presence of that variable and then either retrieve the server information from it or access my local couchDB:

#get service information if on Bluemix  
 if 'VCAP_SERVICES' in os.environ:  
   couchInfo = json.loads(os.environ['VCAP_SERVICES'])['cloudantNoSQLDB'][0]  
   couchServer = couchInfo["credentials"]["url"]  
   couch = couchdb.Server(couchServer)  
 #we are local  
   couchServer = ""  
   couch = couchdb.Server(couchServer) 

Storing new documents is simple and is shown in the full code listing. For the queries I am using the MapReduce feature of couchDB. In a "map" function I return the city name (and just the integer value 1), in the reduce function I am aggregating (summing up) the values by city. Both functions could be defined in the Python script and then passed into Cloudant as part of the query or predefined for more performance. I chose the latter one. So I created a so-called "secondary index" in my Cloudant database, it is called "view" in my couchDB. They are stored as part of a "design document" (shown is Cloudant):

Secondary index / permanent view

With that I finish my Python application, add some calls to the couchDB Python API (which I needed to add to the file "requirements.txt" as dependency) and test it locally. The final step is to deploy the application to Bluemix using the Cloud Foundry tool "cf push". Done, seems to work:
Bluemix weather app with Cloudant stats

Last but not least, here is the code I used for my little app:

 import os  
 from flask import Flask,redirect  
 import urllib  
 import datetime  
 import json  
 import couchdb  
 BASE_URL = ""  
 BASE_URL_fc =""  
 app = Flask(__name__)  
 # couchDB/Cloudant-related global variables  
 #get service information if on Bluemix  
 if 'VCAP_SERVICES' in os.environ:  
   couchInfo = json.loads(os.environ['VCAP_SERVICES'])['cloudantNoSQLDB'][0]  
   couchServer = couchInfo["credentials"]["url"]  
   couch = couchdb.Server(couchServer)  
 #we are local  
   couchServer = ""  
   couch = couchdb.Server(couchServer)  
 # access the database which was created separately  
 db = couch['weather']  
 def index():  
   return redirect('/weather/Friedrichshafen')  
 def weather(city):  
   # log city into couchDB/Cloudant  
   # basic doc structure  
   doc= { "type" : "city",  
     "c_by" : "bm",  
   # we store the city and the current timestamp  
   # and store the document (doc)  
   # Time to grab the weather data and to create the resulting Web page  
   # build URIs and query current weather data and forecast  
   # JSON data needs to be converted  
   url = "%s/%s" % (BASE_URL, city)  
   wdata = json.load(urllib.urlopen(url))  
   url_fc = "%s/%s" % (BASE_URL_fc, city)  
   wdata_fc = json.load(urllib.urlopen(url_fc))  
   # build up result page  
   page='<title>current weather for '+wdata["name"]+'</title>'  
   page +='<h1>Current weather for '+wdata["name"]+' ('+wdata["sys"]["country"]+')</h1>'  
   page += '<br/>Min Temp. '+str(wdata["main"]["temp_min"]-273.15)  
   page += '<br/>Max Temp. '+str(wdata["main"]["temp_max"]-273.15)  
   page += '<br/>Current Temp. '+str(wdata["main"]["temp"]-273.15)+'<br/>'  
   page += '<br/>Weather: '+wdata["weather"][0]["description"]+'<br/>'  
   page += '<br/><br/>'  
   page += '<h2>Forecast</h2>'  
   page += 'Temperatures'  
   page += '<br/>Min: '+str(wdata_fc["list"][0]["temp"]["min"]-273.15)  
   page += '<br/>Max: '+str(wdata_fc["list"][0]["temp"]["max"]-273.15)  
   page += '<br/>Morning: '+str(wdata_fc["list"][0]["temp"]["morn"]-273.15)  
   page += '<br/>Evening: '+str(wdata_fc["list"][0]["temp"]["eve"]-273.15)  
   page += '<br/><br/>Weather: '+wdata_fc["list"][0]["weather"][0]["description"]  
   page += '<br/><br/>'  
   # Gather information from database about which city was requested how many times  
   page += '<h3>Requests so far</h3>'  
   # We use an already created view  
   for row in db.view('weatherQueries/cityCount',group=True):  
    page += row.key+': '+str(row.value)+'<br/>'  
   # finish the page structure and return it  
   page += '<br/><br/>Data by <a href="">OpenWeatherMap</a>'  
   return page  
 port = os.getenv('VCAP_APP_PORT', '5000')  
 if __name__ == "__main__":'', port=int(port))  

1 comment:

sasubillis said...

Excellent tutorial. Got a feel of Bluemix PaaS.


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