Higher Availability of Services in Heterogeneous Distributed Systems

Computing systems are becoming more and more complex and assuming more and more responsibilities in all sectors of human activity. Applications do not run locally on a single computer any more. A lot of today’s applications are built as distributed system where services on different computers are communicating. Distributed systems arise everywhere. The Internet is one of the best-known distributed systems and used by nearly everyone today. It is obvious that we are more and more dependant on computer services. Many people expect to be able to buy things like clothing or electronic equipment even at night on the Internet. Computers are expected to be operational and available 7 days a week, 24 hours a day. Downtime, even for maintenance, is no longer acceptable. The thesis presents a framework for the development of highly available software services. The research focuses on failover functionality and heterogeneous distributed systems that are based on client/server architecture. Failover is the migration of services from one server to another. If one server in the distributed system fails, another server takes over the services of the failed one. The thesis shows how failover functionality can be expressed by attributes and how higher availability of services can be achieved by transparent failover with state replication in heterogeneous distributed systems. Failover requirements are expressed as attributes by using meta information. The advantage is that failover requirements are seamlessly integrated in the development process of a service or system. Furthermore the meta information with the failover requirements have initially no influence on the behaviour of a service or system and can be specified in an easy and efficient way. Meta information with the failover requirements are analysed, processed and transformed in a further process. The advantage is that the specification of functional requirements is easier to read since failover functionality does not become tangled with the basic functionality. The thesis offers a High Availability and Failover Framework (HAFF) that simplifies the development of available services with failover functionality. The designed HAFF is a complete software solution. The framework can be used on simple distributed system with conventional computers. The research is based on the motivation that failover can increase the availability of services dramatically. Today’s development of available systems is very expensive, since every component of the system must be reliable. The proposed framework can decrease the costs to implement availability radically, so that even small business companies will be able to offer highly available services. In comparison to other failover approaches the thesis shows how failover can be achieved by software and used for services in heterogeneous distributed systems. The system is seen in a holistic way and hardware and software failures are tolerated by the proposed framework. The thesis outlines the motivation and objectives of the research, describes the developed framework and reviews literature on distributed systems, availability and meta information. Meta information is used in the framework to increase the efficiency of developers. The thesis presents a generic meta information facility to be able to define and process meta information. A so called Meta Information Definition Language (MIDL) has been designed to define meta information within models (e.g. source code) of different programming languages. A Meta Information Processing Tool (MIPT) and an Abstract Syntax Language Tree (ASLT) have been designed for the processing of meta information and manipulation of the model (e.g. code transformations). The designed meta information facility can be seen as a framework to define macro languages for a programming language. Any language that supports comments can be extended by MIDL specifications. The meta information facility has been designed to simplify the development of failover for services with state replication. Developers only define some attributes to ensure failover. The attributes are specified by a FailOver Point Definition Language (FOPDL), based on MIDL. Code needed in software will be generated automatically by processing the FOPDL specifications. HAFF offers a High Availability and Failover Environment (HAFE) that observes and manages a heterogeneous distribute system. It gives knowledge about alternative available service instances and is used in case of failover. Furthermore, a reference implementation of the proposed HAFF with it’s underlying meta information facility has been designed, developed and tested during research. The reference implementation can be used to demonstrate most of the designed features. It is used in the thesis in order to evaluate the approach by simulations.

Name dc:type.qualificationname

PhD

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

De Montfort University

Year dc:date.issued

2007

Author dc:creator

• Wolke, Karsten

Licence

• https://dora.dmu.ac.uk/bitstreams/af568f2d-a95d-4ac5-99c3-7227a75e20d3/download