BERT-RPC Example (aka Pony-Service)

To demonstrate how the application of BERT-RPC within Ruby could look like I build an API which returns JSON based on remote service calls.

There are two parts in this example:

• PonyAPI
• PonyService

The PonyAPI is the user facing interface wich provides a HTTP-based access and returns JSON encoded data.

The PonyService is an external handler to be used with Ernie. It queries some external resource (i.e. the Wikipedia) and returns some data from that resource. This is done to actually do something and not only return a string.

Setup

To get the example running you need to install Erlang. This is required for the Ernie server. Any version above R13B should work. I recommend installing it via homebrew (homebrew install erlang). Note: This will take some time ;-)

After that you need to run a bundle install in the two projects pony_api and pony_service. Assuming all dependencies got installed you can start the API with bundle exec rackup. The Ernie server is started with bundle exec ernie -c service.cfg -d (to stop it run bundle exec ernie halt).

To test this setup just call the API with curl:

$ curl http://localhost:9292/ponies/Applejack

The result should look like this:

{
  "name": "Applejack",
  "description": "Applejack is an earth pony
    with an orange body and blonde mane and tail. Originally, she was
    featured in the 1984 TV special, and has almost the same appearance
    with the Generation 1 counterpart, but speaks with a Southern
    American accent and having fewer apples on her cutie mark.[2]
    Applejack is very dependable and down-to-earth, but also tends to
    act stubborn. She wears a brown cowboy hat and is the only one of
    the six main characters who keeps her mane and tail tied back,
    instead of letting them fall loose. Applejack comes from a large
    family of ponies with apple-related names, spread all over
    Equestria, who oversee apple orchards and run a group of businesses
    to sell apples and products made from them.[1] She works in her farm
    Sweet Apple Acres, where she lives with her younger sister Apple
    Bloom, older brother Big Macintosh and Granny Smith. Applejack has
    demonstrated her strength and dexterity on many occasions, and she
    is also very skilled with a lasso. She represents the element of
    honesty. She has a pet Border Collie named Winona."
}

What happened?

In short here is what happened:

• The curl request hit a Sinatra app which handles the JSON encoding
• The Sinatra app will call the PonyService via BERT-RPC
• The request to the service implementation is handled by Ernie
• The request is passed to the Ruby implementation
• The service implementation will reach out to Wikipedia, get information about the requested pony and will pass it back as a Ruby hash
• The Ruby hash is serialized, transferred back to the API and there deserialized
• The API will encode it as JSON and respond with the JSON payload to the curl request

Have Fun ;-)