The OpenCPU System

What is OpenCPU

The OpenCPU system exposes an HTTP API for scientific computing to build scalable analysis and visualization modules for use in systems, pipelines, and web applications.

curl https://public.opencpu.org/ocpu/library/stats/R/rnorm/json \
-H "Content-Type: application/json" -d '{"n":3, "mean": 10, "sd":10}'

[4.9829, 6.3104, 11.411]

This maps to the following request

#library(jsonlite)
args <- fromJSON('{"n":3, "mean": 10, "sd":10}')
output <- do.call(stats::rnorm, args)
toJSON(output)

Which is equivalent to this function call

rnorm(n=3, mean=10, sd=10)

What OpenCPU does:

• Interoperable HTTP for data analysis
• RPC and object management
• I/O: JSON, Protocol Buffers, CSV
• Support for parallel/async requests
• Highly configurable security policies
• Native reproducibility
• Client libraries: JavaScript, Ruby, ...

OpenCPU does not

• No predefined widgets
• No special programming paradigms
• No need to manage processes, users, code evaluation, etc. Yet state and privacy!

Keys and objects

curl -v https://demo.ocpu.io/stocks/R/smoothplot -d 'ticker="GOOG"&from="2013-01-01"'

> POST /stocks/R/smoothplot HTTP/1.1
> User-Agent: curl/7.30.0
> Content-Type: application/x-www-form-urlencoded

< HTTP/1.1 201 Created
< Location: https://tmp.ocpu.io/x081cca8c23/
< Cache-Control: max-age=300, public
< Access-Control-Allow-Origin: *
< X-ocpu-session: x081cca8c23
< X-ocpu-r: R version 3.1.0 (2014-04-10)
< X-ocpu-locale: en_US.UTF-8
< X-ocpu-time: 2014-06-26 17:29:32 PDT
< X-ocpu-version: 1.4.3
< x-ocpu-cache: MISS

• Each requests stateless (HTTP)
• No single, permanent R process

Instead: "functional state"

• Each RPC stores object and returns key. No side-effects.
• Use key to retrieve or re-use stored object

Privacy?

• No users! Each key is secret
• Keys initially only known to creator
• But: you are free to share/publish keys
• Basis of "social" analysis

• App is simply a package with web pages
• Web pages call R functions via Ajax

//JavaScript client code
var ticker = $("#ticker").val();    
var req = $("#plotdiv").rplot("smoothplot", {
    ticker : ticker,
    from : "2013-01-01"
})

Results in:

smoothplot(ticker=ticker, from="2013-01-01")

Which is the basis of the stocks app and this jsfiddle.

Bridges to R are available for most popular languages and environments:

• RInside (C++)
• rpy2 (python)
• JRI (Java)
• RinRuby
• rApache
• littler
• RServe (socket)
• RDCOM (windows, excel)

So why would you want to use OpenCPU?

An hello-world example from the rserve manual:

RConnection c = new RConnection();
double d[] = c.eval("rnorm(10)").asDoubles();

• Client needs to generate R syntax
• Client needs to read/manipulate internal R data types
• Client needs to manage R processes
• Limited exception handling
• No concurrency
• Result: high coupling
• Need cross-language expert to get this to work
• Fragmentation of efforts by language/environment

OpenCPU layers on a standardized application protocol (HTTP) to provide an API for statistical computing and visualization (with R, or something else...).

Benefits of HTTP

• Mature, very flexible application protocol
• Interoperable (both client and server!)
• Distributed (using simple URLs)
• Native exception handling (status codes)
• Many features get built-in by design (caching, encryption, authentication, etc)
• Clients widely available
• Implemented in all browsers

• API describes logic of data analysis
• Independent of client/application
• Independent of computational language
• Same API could be implemented in Julia, Python, Matlab

Important API concepts:

1. Objects
2. Graphics
3. Data
4. Manuals
5. Namespaces
6. Function calls

HTTP Methods

Current API uses GET and POST methods. Get is for retrieving objects, POST is for RPC.

Try it!

• https://public.opencpu.org/library/ocpu/{pkg}/
• https://demo.ocpu.io/{pkg}/

HTTP Status Codes

Package resources

Session resources

Content-types

Executing Scripts

Free public demo server:

• https://public.opencpu.org/ocpu/

Single-user development server:

install.packages("opencpu")
library(opencpu)

Ubuntu Linux cloud server

#requires Ubuntu 14.04
sudo add-apt-repository ppa:opencpu/opencpu-1.4
sudo apt-get update
sudo apt-get install opencpu

• Github Webhook: https://public.opencpu.org/ocpu/webhook
• Your package: https://yourname.ocpu.io/pkgname/

API documentation

• https://www.opencpu.org/api.html

Example Apps

• https://www.opencpu.org/apps.html
• https://github.com/opencpu

Papers

• https://www.opencpu.org/research.html
• http://arxiv.org/a/ooms_j_1