06-08-2011, 11:02 AM
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1 INTRODUCTION
Operating system was originally developed to provide a set of common systems services, such as I/O, communication and persistent storage, to simplify application programming. With the advent of multiprogramming, this charter expanded to include abstracting shared resources so that they were as easy to use (and sometimes easier) as dedicated physical resources. The introduction of local area networks in 80’s expanded this role even further. A goal of network operating systems such as Locus, Mach, Sprite and Amoeba was to make remote resources over the LAN as easy to use as local resources, in the process simplifying the development of distributed applications.
With analogy to these systems, argues that it is time to provide a common set of services for wide area applications, in effect to make wide area resources as easy to use as those on a LAN. The past few years has seen a dramatic increase in the number and variety of services that are available over the internet, beyond simple documents to a wide variety of on-line services, such as search engines, real-time news, weather forecasts, interactive games and chat room, airplane reservations and ticketing, to name just a few.
Today, although the World Wide Web has made geographically distributed read-only data easy to use, geographically distributed computing resources are not. The result is that wide area applications that require access to remote CPU cycle, memory, or disk must be programmed in an ad-hoc and application-specific manner. For example, many popular services, such as Digital’s Alta Vista or Netscape’s download page, are geographically replicated to improve bandwidth, reduce latency, and improve availability-no single connection onto the Internet can support tens of millions of users. This situation will only get worse; it is currently predicted that the number of Internet users will increase by an order of magnitude to over 100 million in less than 5 years.
To address these problems, we have built WebOS, a framework for supporting applications that are geographically distributed, highly available, incrementally scalable, and dynamically reconfiguring. WebOS includes mechanisms for resource discovery, a global namespace, remote process execution, resource management, authentication and security .The WebOS used to demonstrate the synergy of these services in simplifying the development of wide area distributed applications and in providing more efficient global resource utilization.
The WebOS framework enables a new paradigm for Internet services.
Instead of being fixed to a single location, services can dynamically push parts of their responsibilities out onto Internet computing resources, and even all the way to the client.
Characteristics
In addition to demonstrating the synergy of a common framework for wide area distributed applications, made a number of specific contributions.
• First, demonstrated and extensible mechanism for running service-specific functionality on client machines and show that this allows for more flexible implementation of name resolution, load balancing, and fault tolerance.
• Second, provided a file system abstraction that combines persistent storage with efficient wide-area communication pattern; demonstrated that this simplifies the implementation of a number of wide area applications.
• Next, presented a methodology for coherently caching program results through the file system, speeding the performance of applications which must repeatedly execute programs with common inputs. Finally, demonstrated how Rent-A-Server, an application developed in our framework, both improves system performance and more efficiently utilizes system resources for Web server access.
2 WebOS Overview
In this section, we provide a brief overview of the major WebOS components; together, they provide the wide area analogue to local area operating system services, to make using geographically remote resources easier to use. Each of these components is operational in our current prototype.
Resource Discovery: Many wide area services are geographically distributed. To provide the best overall system performance, a client application must be able to dynamically locate the server able to deliver the high quality of service. In WebOS, resource discovery includes mapping a service name to multiple servers, an algorithm for balancing load among available servers, and maintaining enough state to perform fail-over if a server becomes unavailable. These operations are performed through Smart Clients, which flexibly extended service-specific functionality to the client machine.
Wide Area File System: To Support replication and wide-scale sharing, WebOS provides a cache coherent wide area file system. WebOS extends to wide area applications running in a secure HTTP name space the same interface, caching, and performance of existing distributed file systems. In addition, we demonstrate the benefit of integrating the file system with application-controlled efficient wide area communication.
Security and Authentication: To support applications operating across organizational boundaries, WebOS defines a mode of trust providing both security guarantees and an interface for authenticating the identity of principals. A key enabling feature is fine-grained control of capabilities provided to remote processes executing on behalf of principals.
Process Control: In WebOS, executing a process on a remote node should be as simple as the corresponding local operation. The underlying system is responsible for authenticating the identity of the requester and determining if the proper access rights are held. Precautions must be taken to ensure that the process does not violate local system integrity and that it does not consume more resources than allocated to it by local system administrators.
As an explicit design choice, we leverage as much functionality as possible from existing low level services. For example, for compatibility with existing applications, we adopt IP address and URL’s for the global name space. TCP is used to provide reliable communication, while SSL is used for page link level security.
