Application Concepts

The intend of this wiki page is to document the key concepts around CDAP Application.

Artifacts repository

• Deployed JARS
  • Can be application, can be plugin or anything that CDAP supports.
  • Identified by type, name and version.
  • Deployed JARS are immutable
    • For snapshot jar deployment, the deployment timestamp will be used to generate a unique version
      • Similar to how maven repo works

Application

• An Application can declares what configuration properties it needs

• Configure method to generate Application Specification
  • A set of properties can be submitted on application deployment and available in the Application.configure method
    • Application can configure itself based on those properties
• Application can be extended by cloning. Conceptually it is like prototypal inheritance. There is no class (template), only instance (Application).
  • On cloning, a set of properties can be submitted through the clone (REST) call
  • The Application.configure() method will be called again to generate a new Application Specification for the newly cloned app
    • The set of properties submitted through the clone call will be merged with the source app properties
    • There can be a known set of properties that the platform will interpret automatically (same applies to the original app deployment)
      • Adding of schedulers, plugins usage, etc.
  • No jar is being copied, only new entries in meta data table are created

Program

• A Program can declares what configuration properties it needs
  • Much like what plugin does
  • Properties will be populated and available in both configure time and run time.

Properties

There are three places where property values can be defined:

• When application is configured
• Per cluster (preferences store)
• When program starts (runtime arguments)

When a program runs, property values defined in all these places should be merged to form a single set of properties with the precedence of

  Application configure < Preferences store < Runtime arguments

Some properties can be marked as "final" so that it cannot be modified after application configured.

• Do we need "final" at different level?