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[3] Non versioned solution: Running two separate applications with services communicating to the same dataset and having an upstream device implement url routing is identical to us implementing an "evergreen" url

Feature Request: Multiple Application Versions with Rollback capabilities.  Customers would like the ability to throttle requests between multiple versions of an application and service.   

Requirements

• User can deploy a new version of an Application while keeping the old one.
• User can control the lifecycle of a Program from a particular Application version.
• The same Service program from different Application versions can be running concurrently.
• User can control the routing of incoming Service requests to different Service versions by percentage.
• User can make Service requests to a version specific endpoint.

Design

• Introduce versioning for Application
  • Application is created from Artifact, which already has versioning.
  • Upon Application creation, increment the Application version by one.
• Introduce version specific REST endpoint for Application
  • Path prefix as <base-url>/namespaces/<namespace>/apps/<app-id>/versions/<app-version>
  • Most of the endpoints in http://docs.cdap.io/cdap/current/en/reference-manual/http-restful-api/lifecycle.html will have a version specific variant.
    • Except the one for create Application.
  • Existing non-version specific endpoints are aliases to the latest Application version.
• The same Service of different Application versions can be started and running concurrently.
  • All of them will publish under the same service name in ZK.
  • The Application version will be stored inside the ephemeral node created by that particular Service version.
• Introduce version specific REST endpoint for Service routing
  • Request path is <base-url>/namespaces/<namespace>/apps/<app-id>/versions/<app-version>/services/<service-id>/methods/<endpoint-path>
• Router is aware of the Service version during routing
  • For version specific endpoints, router will only route to those who have matching version based on version information stored in the ZK node.
  • For non-version specific endpoints, router can optionally take a version distribution configuration.
    • The configuration is stored in a ZK node
      • New REST API exposes from app-fabric to set the distributed for a given service
      • Router will watch for changes in that node to get hold of updates in distribution
    • Router will route requests based on the distributed configuration
    • If the configuration is missing, it will just route randomly to all available Service containers