Google App Engine is pretty great (if you go all the way)

So I'm starting to bang around another project. As I describe it on my Careers 2.0 profile:

Project is still in its infancy but it will have server (GAE-hosted Python program evaluating JSON feeds of stock data with Cloundant [CouchDB] backend) and mobile (Android app to visualize/manipulate the data from Cloundant) components. There really isn't a point behind this program and I don't necessarily condone algorithmic trading - it's just a fun hack.

Or so I thought. Doesn't look like I'll be using Google App Engine because I don't want to do it the "GAE way" (not that there's anything wrong with that). Deploying an app to GAE is super simple but I ran into problems when starting to incorporate 3rd-party libraries (couchdbkit and restkit to be exact). These libs are too small to be part of the standard runtime environment. It's interesting to note that even Django is implemented in a slightly different way on GAE.

I'll spare the details (though they are available in my stackoverflow question) but I was having importing couchdbkit into my script. It was choking on things likes sockets and resources, which made me think I was running afoul of the sandbox rules:

An App Engine application cannot:

• write to the filesystem. Applications must use the App Engine datastore for storing persistent data. Reading from the filesystem is allowed, and all application files uploaded with the application are available.
• open a socket or access another host directly. An application can use the App Engine URL fetch service to make HTTP and HTTPS requests to other hosts on ports 80 and 443, respectively.
• spawn a sub-process or thread. A web request to an application must be handled in a single process within a few seconds. Processes that take a very long time to respond are terminated to avoid overloading the web server.
• make other kinds of system calls.

I put a question on the Cloudant discussion board and got not 1 but 2 answers from Cloudant techs within an hour (these dudes are good - I don't even have a paying account and they are very responsive). Anyway, they tipped me off to this telling Quora answer. It looks like the Django/Python hosting space is about to blow up with Heroku-like solutions.

Both the Cloudant tech and Django responder (a Django co-inventor) had good things to say about WebFaction. It is not a free hosting service ($9.50 per month and goes down with longer term contracts). After a quick Q&A session with a sales rep, I took the plunge. 1 hour later, my program was working perfectly on my WebFaction account. Success! The only thing that makes me nervous is having to do any sys admin stuff at all - getting my script and installations to reference the right Python version (WebFaction comes everything from 2.4 [default] up through 3.2) is about all I care to handle.

Python + Couchdbkit = nice

So I'm working on a CouchDB project and you can read more about what I'm doing on the mobile side here.. There will be a server-side component and I want to get my feet wet with Python. I'm currently working through the tutorial but like most people I learn more by doing.

There are several CouchDB libraries for Python but I went with Couchdbkit. This decision was influenced by a post on the Cloudant discussion board stating Couchdbkit and Cloudant should work well together. So far, I have to agree.

The installation instructions for Couchdbkit are pretty straight forward. For the record, I'm using Python 2.6.6. I did find I needed to use restkit for HTTP resources. I set my sights low - I just wanted to get the program of Couchdbkit's Getting Started page to work. Username/password redacted to protect the innocent:

#! /usr/bin/env python

import datetime
from couchdbkit import *
from restkit import BasicAuth

class Greeting(Document):
    author = StringProperty()
    content = StringProperty()
    date = DateTimeProperty()

server = Server('https://[username].cloudant.com/', filters=[BasicAuth('[usename]', '[password]')])
db = server.get_or_create_db("greeting")

Greeting.set_db(db)
greet = Greeting(
    author="Benoit",
    content="Welcome to couchdbkit world",
    date=datetime.datetime.utcnow()
)
greet.save()


There are more exercises on the Getting Started page including an introduction to views. This worked as advertised with no need to change the supplied code.

Rocking and rolling with Ektorp and Cloudant

My first Android app was developed using AWS' SimpleDB. While I like the Android SDK, I'm not terribly satisfied with the performance I'm getting. As far as NoSQL databases go, CouchDB is getting really great press. Cloudant is a well-respected YC-aligned startup which hosts CouchDB databases. I decided to give it a try, as I'd like to get deeper into JSON as well (generally, SimpleDB uses XML while CouchDB uses JSON).

Ektorp is one of several Java APIs for CouchDB but it doesn't look like many people (anyone as far as I can tell) are using it with Cloudant. So I decided to give it a try just for fun.

First off, Ektorp requires a lot of external JARs (9 or 10 from what I see). Importing the 1 org.ektorp JAR and 8-9 other JARs into an Eclipse project quickly proved tiresome. Ektorp recommends using Maven, which manages all dependencies. Better yet, m2eclipse offers a way to integrate Maven with Eclipse. The setup instructions and videos are very self-explanatory. Dropping the supplied Ektorp entry into my pom.xml was simple. All required dependencies were quickly and correctly imported. Piece of cake.

Okay, now to connect to Cloudant. Getting a free Cloudant account is easy. The database UI is clean and simple. I want to be a good coder and use SSL, which Cloudant can certainly support. Ektorp supplies a good API tutorial which accomplishes what I want to start off with:

HttpClient httpClient = new StdHttpClient.Builder()
.host("localhost")
.port(5984)
.build();

CouchDbInstance dbInstance = new StdCouchDbInstance(httpClient);
CouchDbConnector db = new StdCouchDbConnector("mydatabase", dbInstance);

db.createDatabaseIfNotExists();

Initial attempts proved unsuccessful as I couldn't figure out what .host() to use. The supplied documentation wasn't clicking - on to StackOverflow where I'm sure someone's dealt with something similar before. Not being able to add an "ektorp" tag to my question leads me to believe the library isn't as prevalent as I thought. No worries, someone was able to kindly point out I shouldn't be including "http://" or "https://" in my host variable. Oh yeah. Read my StackOverflow question for the details. So I was able to get it working using http as follows:

HttpClient httpClient = new StdHttpClient.Builder()
.host("[username].cloudant.com")
.port(5984)
.username("[username]")
.password("[password]")
.build();

Getting SSL to play nice proved difficult. Using port 443 didn't readily work until someone from Cloudant wisely told me to RTFM. Okay, adding .enableSSL(true) and .relaxedSSLSettings(true) is a good point but I was still getting an IllegalStateException and the stack trace indicated it was trying to use http after initializing my object with https. Huh? Finally, after scouring the Ektorp discussion board, I found this post which indicated Ektorp 1.1.1 included SSL-related bug fixes. So I updated my pom.xml to look for 1.1.1 vice 1.1.0. Recompile Maven, run Java application, success! Database added to my cloudant account via https.

I was getting an annoying but non-fatal exception relating to SLF4J:

Failed to load class "org.slf4j.impl.StaticLoggerBinder"

This is fairly common. Manually adding slf4j-simple-X.jar (slf4j-simple-1.6.1.jar to be exact) to the project resolved the issue.

So this is my super-complex program:

HttpClient httpClient = new StdHttpClient.Builder()
.host("[username].cloudant.com")
.port(443)
.username("[username]")
.password("[password]")
.enableSSL(true)
.relaxedSSLSettings(true)
.build();

CouchDbInstance dbInstance = new StdCouchDbInstance(httpClient);
CouchDbConnector db = new StdCouchDbConnector("httpsdatabase", dbInstance);

db.createDatabaseIfNotExists();

and remember to make ektorp's dependency look for version "1.1.1" in your pom.xml.