Liquid Web Services

Cesare Pautasso
http://www.pautasso.info
[email protected]
@pautasso

Liquid Quality Attributes

Scalability

Adaptability

Flexibility

Elasticity

WWW 2011

Some Constraints

Fine-grained Decomposition

Global Addressability

Underspecified Communication

Uniform Interface

WICSA 2011

The S Scripting Language

for Scalable, Stateful, Services

PPOPP 2012

Hello World

service S { 
  res '/hello' on GET { 
  //handle GET request
    respond 'World!'; 
  }
}

Request handlers contain any JavaScript code
(with some S extensions)

Service Composition

service Composition { 
  res '/hello1' on GET { 
    respond get 'http://api.inf.usi.ch/'; 
  }
  res '/hello2' on GET { 
    respond get '/hello1'; 
  }
}

Stateful Services

service Stateful { 
 res '/helloState' {
  state s = 'World'
  on GET { 
    respond 'Hello' + s
  }
  on PUT { 
   s = req.name
  }
 }
}

S Runtime

• Compiled to JavaScript, S scripts run on the node.js framework
• The S runtime extends node.js with support for parallelization and automatic reconfiguration

• Each request handler runs in a separate node.js worker process
  (Global Addressability, Fine-grained Decomposition)
• Handlers of stateless resources can be replicated and migrated dynamically at will (Uniform Interface)
• Handlers of stateful resources use a master-slave replication style (Uniform Interface)
• Communication between node.js processes uses an optimized protocol, while HTTP is used to interact with the external world (Underspecified Communication)

Conclusion

• The "Liquid" physical properties is a good metaphor for intrinsically adaptable software, which can be seamlessly deployed across heterogeneous execution platforms (Clouds, multicores).
• The S language extends JavaScript with architectural-level constructs to build RESTful Web services, which also embody the constraints of the liquid architectural style