Java Data Intensive Serving Container - JDisc

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Vespa's Java container - JDisc, hosts all application components as well as the stateless logic of Vespa itself. Which particular components are hosted by a container cluster is configured in services.xml. The main features of JDIsc are:

• HTTP serving out of the box from an embedded Jetty server, and support for plugging in other transport mechanisms.
• Integration with the config system of Vespa which allows components to receive up to date config (by constructor injection) resulting from application deployment.
• Dependency injection based on Guice (Felix), but extended for configs and component collections.
• A component model based on OSGi which allows component to be (re)deployed to running servers, and to control which API's they expose to others.
• The features above combine to allow application package changes (changes to components, configuration or data) to be applied by Vespa without disrupting request serving nor requiring restarts.
• Standard component types exists for
  • general request handling
  • chained request-response processing
  • processing document writes
  • intercepting queries and results
  • rendering responses
  Application components can be of any other type as well and do not need to reference any Vespa API to be loaded and managed by the container.
• A general chain composition mechanism for components.

Developing Components

• The JDisc container provides a framework for processing requests and responses, named Processing - its building blocks are:
  • Chains of other components that are to be executed serially, with each providing some service or transform
  • Processors that change the request and / or the response. They may also make multiple forward requests, in series or parallel, or manufacture the response content themselves
  • Renderers that are used to serialize a Processor's response before returning it to a client
• Application Lifecycle and unit testing:
  • Configuring components with custom configuration
  • Component injection allows components to access other application components
  • Learn how to build OSGi bundles and how to troubleshoot classloading issues
  • XML processing with JAXB and JAXP (DOM, SAX, StAX)
  • Using Libraries for Pluggable Frameworks from a component may result in class loading issues that require extra setup in the application
  • Unit testing configurable components
• Handlers and filters:
  • Http servers and security filters for incoming connections on HTTP and HTTPS
  • Request handlers to process incoming requests and generate responses
• Searchers and Document Processors:
  • Searcher and search result renderer development
  • Document processing

Reference documentation

• services.xml

Other related documents

• Versioning Components
• Client providers are capable of connecting to and forwarding requests to a remote server on a specific protocol, e.g. the HttpClient is a client provider for HTTP and HTTPS
• To accept incoming connection on other protocols than HTTP/HTTPS, develop custom server providers starting with the tutorial
• The Chain Builder API
• Designing RESTful web services as Vespa Components
• healthchecks - using the Container with a VIP
• Vespa Component Reference: The Container's request processing lifecycle