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An Infrastructure for Network Computing with Java Applets Arash Baratloo, Mehmet Karaul, Holger Karl, and Zvi M. Kedem Department of Computer Science Courant Institute of Mathematical Sciences New York University http://www.cs.nyu.edu/milan.

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Presentation Transcript
slide1

An Infrastructure for

  • Network Computing with Java Applets
  • Arash Baratloo, Mehmet Karaul, Holger Karl, and Zvi M. Kedem
  • Department of Computer ScienceCourant Institute of Mathematical SciencesNew York University
  • http://www.cs.nyu.edu/milan

Partially supported by: DARPA/Rome Laboratory, NSF, Intel, Microsoft

goals
Goals
  • Java programming language + Java-capable Web browsers are a great “one-two punch,” but…
  • The challenge is to fully utilize this potential given the limitations imposed by browsers.
  • In the context of Web-based parallel programming environments and collaborative applications, identify a set of problems, and ...
  • Provide a set of unified solutions
typical web based collaborative session
Typical Web-basedCollaborative session
  • Composed of
    • A single Java applications process
    • Multiple partner applets
  • Applets down-loaded from the application host
  • Applets communicate only with the application host
  • This is the context of our work
  • Examples are TANGO, JavaParty, Java Collaborator Toolset, etc
charlotte pdcs 96 in a nutshell
Charlotte (PDCS’96) in a Nutshell
  • Parallel programming model and system that provides
    • Predictable virtual machine to the programmer
    • Realizes the virtual machine on the unpredictable Web
  • End-user starts the execution of the manager process
  • Volunteers join the computation by a click of a mouse
  • Worker (applets) code and data is downloaded
  • One-click computing!
  • Other examples are Javelin, Bayanihan, etc.
issues to address
Issues to Address
  • In the context of Web-based collaborative and parallel applications, …
  • How do end-users find a service?
    • E.g., how do volunteers find computations?
    • E.g., how do users find multi-player games?
  • Are users free to execute the application on any host?
    • Not all accessible machines run HTTP servers
  • How do collaborative applets communicate with each other?
    • Centralized forwarding agent?
    • Untrusted native code?
roadmap
Roadmap
  • Goals and Motivations
  • Architecture
  • Directory Service
  • Class Server
  • Direct Inter-applet communication
  • Security Issues
  • Summary
knittingfactory architecture
KnittingFactory Architecture
  • Infrastructure (middle-ware) to support both
    • High-level systems, e.g, parallel programming, collaborative environments, etc.
    • Web-based applications
  • Integrated services for
    • Directory service
    • Class server
    • Inter-applet communication
roadmap1
Roadmap
  • Goals and Motivations
  • Architecture
  • Directory Service
  • Class Server
  • Direct Inter-applet communication
  • Security Issues
  • Summary
knittingfactory directory service
KnittingFactory Directory Service
  • For highly dynamic (sometimes short lived) services that frequently register and unregister.
  • Considerations…
    • Distributed -- a necessity for the Web
    • Directory-server processes should not do all the work (unlike LDAP) -- scalability
    • Caching servers (and replication) require invalidation -- costly
    • Must support Web browsers -- simple language
  • Goal: Move most the computation and the search away form directory-server process and onto the Web browser.
directory service comprises of
Directory Service Comprises of...
  • Existing HTTP servers act as directory-server processes
  • A single HTML file contains all the necessary information
    • Other servers, e.g., <name,URL>
    • Registered services, e.g., <name,URL>
    • Program code, i.e., Java Script
  • CGI scripts to register/unregister services
  • Forms a directed graph
registration successful lookup
Registration & Successful lookup
  • Register/Unregister
    • Service provider sends an HTML Post message <name,URL>
    • Directory server executes one of the CGI scripts
    • Results in adding/removing an entry in the HTML file
  • Successful lookup
    • Client requests the HTML file containing data + Java Script code
    • The program searches the file it came from for the appropriate entry
unsuccessful lookup
Unsuccessful lookup
  • The program picks the next server (referral) to visit, assembles a new URL, and redirects the Web-browser
  • Browser loads a new HTML file which wipes out the program state!
  • The newly loaded Java script program starts executing and…
  • Reads the state information passed as a URL tag (#)!
  • Search is performed by the clients!
  • Implemented BFS
roadmap2
Roadmap
  • Goals and Motivations
  • Architecture
  • Directory Service
  • Class Server
  • Direct Inter-applet communication
  • Security Issues
  • Summary
issues
Issues...
  • Java application process requires an HTTP server running on the same host, but…
    • Users might not have access to hosts running HTTP servers
    • HTTP servers machines will become overloaded when hosting many applications
    • HTTP servers are too “heavy-weight” for a simple…
  • Coupling class servers with an application can...
knittingfactory class server
KnittingFactory Class Server
  • Embedded Java class (applet code) server to…
  • … flexibly execute the application program on any host
  • … provide a convenient gateway for browsers to communicate with applications
  • That simple!
roadmap3
Roadmap
  • Goals and Motivations
  • Architecture
  • Directory Service
  • Class Server
  • Direct Inter-applet communication
  • Security Issues
  • Summary
inter applet communication
Inter-Applet communication
  • Browsers enforce the “host-of-origin” policy as a security measure: an applet is not allowed to:
    • Listen for network connections
    • Initiate a connection to any host other than the one it came from
  • Typical solutions
    • Use a centralized forwarding agent to route messages (e.g, Javelin, Java Collaborator Toolset)
    • Use untrusted code as in plug-ins and native code (e.g, TANGO, ATLAS)
  • But forwarding agent can become...
    • A bottle-neck and a single point of failure
  • And with native code…
    • Unsafe, not portable and heterogeneous anymore
inter applet communication continue
Inter-Applet communication (continue)
  • Signed applets (JDK1.1) and fine-grain access control (JDK1.2) is too rigid for every-day users
    • Developers have to obtain a certificate and a digital ID from Certifying Authority (CA)
    • Users/administrators have to decide who to trust and how much
  • Wouldn’t it be nice to have direct applet-to-applet communication?
  • KnittingFactory Applets Can!
    • Implemented using Java RMI,
    • JDK1.1.3 and tested with appletviewer and HotJava 1.1
  • Security issues will be discussed later
knittingfactory applet
KnittingFactory Applet
  • In a nutshell
    • Each applet passes a Remote Reference of itself to the session manager
    • Manager propagates the reference to other session members
    • After that point, applets can communicate directly
  • Applets form a collaborative session simply by inheriting KF_Applet
  • Simplifies collaborative applications development
roadmap4
Roadmap
  • Goals and Motivations
  • Architecture
  • Directory Service
  • Class Server
  • Direct Inter-applet communication
  • Security Issues
  • Summary
security issues
Security Issues
  • It is apparent that KnittingFactory Applets violate the host-of-origin policy, and…
  • It might be used to break Java security guarantees
    • Many thanks to Java’98 PC, referees, and many others for bringing this to our attention
  • The benefits of direct inter-applet communication is obvious, and…
  • Just as a forwarding agent can forward messages,

It might be possible to forward trust (references) in a safe and efficient manner.

roadmap5
Roadmap
  • Goals and Motivations
  • Architecture
  • Directory Service
  • Class Server
  • Direct Inter-applet communication
  • Security Issues
  • Summary
summary of services
Summary of services...
  • Distributed directory service
    • Designed for services that frequently register/unregister
    • Designed for Web browsers to act as clients
    • Search is performed by the browsers
    • As much as possible, does not introduce new processes/daemons
  • Class Server
    • Simple, but execution flexibility
    • Convenient gateway to the application
  • Inter-applet communication
    • Simplifies collaborative application development
    • Removes single point of failure
    • Does not require native code
  • Open question: can we guarantee safety while maintaining flexibility of inter-applet communication?