Various High Availability DataBase systems (HADB) are used to provide high availability. Pairing an active database system with a standby system is one commonly used HADB techniques. The active system serves read/write workloads. One or more standby systems replicate the active and serve read-only workloads. Though widely used, this technique has some significant drawbacks: The active system becomes the bottleneck under heavy write workloads. Replicating changes synchronously from the active to the standbys further reduces the performance of the active system. Asynchronous replication, however, risk the loss of updates during failover. The shared-nothing architecture of active-standby systems is unnecessarily complex and cost inefficient. In this thesis we present SHADOW systems, a new technique for database high availability. In a SHADOW system, the responsibility for database replication is pushed from the database systems into a shared, reliable, storage system. The active and standby systems share access to a single logical copy of the database, which resides in shared storage. SHADOW introduces write offloading, which frees the active system from the need to update the persistent database, placing that responsibility on the underutilized standby system instead. By exploiting shared storage, SHADOW systems avoid the overhead of database-managed synchronized replication, while ensuring that no updates will be lost during a failover. We have implemented a SHADOW system using PostgreSQL, and we present the results of a performance evaluation that shows that the SHADOW system can outperform both traditional synchronous replication and standalone PostgreSQL systems.

The thesis is focused on use and implement High Availability cluster in the productive environment, where is needed to concentrate on business critical application. The main aim of this thesis is to create the environment for callback system, which consist from many software products, for example database, web, java and etc. A company has to consolidate every application in an flexible environment resistent to hardware failure, human error in order to be running 24/7.

Cílem práce je podat ucelený přehled o aktuálních technologiích sloužících k zajištění dostupnosti IT infrastruktury v podniku. Autor má zkušenosti nejen s konkrétními technologiemi a přístupy k zajištění vyšší odolnosti jednotlivých komponent serveru vůči výpadku (ukládání dat, napájení, řízení toku vzduchu, ochrana paměti, ?) , ale i se softwarovými produkty, které zajistí redundanci celého serveru. Tento přístup byl otestován i v případové studii, kde proběhla analýza stávající situace ve vybrané společnosti a nalezeny funkce poskytované jednotlivými komponentami infrastruktury. Kromě detailního zmapování situace byla nalezena i slabá místa a doporučeno řešení.

In recent years, cloud storage systems have become very popular due to their good scal- ability and high availability. However, these storage systems provide limited transactional capabilities, which makes developing applications that use these systems substantially more difficult than developing applications that use a traditional SQL-based relational database management systems (DBMS). There have been solutions that provide transactional SQL-based DBMS services on the cloud, including solutions that use cloud shared storage systems to store the data. However, none of these solutions take advantage of the shared cloud storage architecture to provide DBMS high availability. These solutions typically deal with the failure of a DBMS server by restarting this server and going through crash recovery based on the transaction log, which can lead to long DBMS service downtimes that are not acceptable to users. It is possible to run traditional DBMS high availability solutions in cloud environments. These solutions are typically based on shipping the transaction log from a primary server to a backup server, and replaying the log at the backup server to keep it up to date with the primary. However, these solutions do not work well if the primary and backup are in different, geographically distributed data centers due to the high latency of log shipping. Furthermore, these solutions do not take advantage of the capabilities of the underlying shared storage system. We present a new transparent high availability system for transactional SQL-based DBMS on a shared storage architecture, which we call CAC-DB (Continuous Access Cloud DataBase). Our system is especially designed for eventually consistent cloud storage systems that run efficiently in multiple geographically distributed data centers. The database and transaction logs are stored in such a storage system, and therefore remain available after a failure up to the failure of an entire data center (e.g., in a natural disaster). CAC-DB takes advantage of this shared storage to ensure that the DBMS service remains available and transactionally consistent in the face of failures up to the loss of one or more data centers. By taking advantage of shared storage, CAC-DB can run in a geographically distributed environment with minimal overhead as compared to traditional log shipping solutions. In CAC-DB, an active (primary) and a standby (backup) DBMS run on different servers in different data centers. The standby catches up with the active's memory state by replaying the shared log. When the active crashes, the standby can finish the failover process and reach peak throughput very quickly. The DBMS service only experiences several seconds of downtime. While the basic idea of replaying the log is simple and not new, the shared storage environment poses many new challenges including the need for synchronization protocols, new buffer pool management mechanisms, approaches for guaranteeing strong consistency without sacrifi cing performance and new shared storage based failure detection mechanism. This thesis solves these challenges and presents a system that achieves the following goal: if a data center fails, not only does the persistent image of the database on the storage tier survive, but also the DBMS service can resume almost uninterrupted and reach peak throughput in a very short time. At the same time, the throughput of the DBMS service in normal processing is not negatively affected. Our experiments with CAC-DB running on EC2 con rm that it can achieve the above goals.

This thesis describes development and verification of application for support of HACMP clustering education in IBM AIX OS. In fact, development of this application can help students to understand basic functions of this type of cluster. Users, eventually, can verify full function of input configuration cluster in real environment. Ultimately, it can simulate basic cluster function and create basic configuration file, which can be direct apply to operational installation of HACMP software of version 5.3.

Este trabalho procura averiguar as dificuldades e os problemas envolvidos na especificação e implementação de uma arquitetura de objetos de serviço para gerenciamento e suporte a aplicações distribuídas em uma plataforma de computadores em configuração tipo cluster, em particular daqueles que devem cumprir requisitos de alta disponibilidade. Tal arquitetura deve apresentar-se como uma infra-estrutura distribuída de serviços e compor uma camada intermediária entre as partes das aplicações distribuídas e os recursos do cluster, compondo desse modo uma camada de middleware. Uma arquitetura de gerenciamento e de suporte a aplicações distribuídas, para que possa atingir plenamente seus objetivos, deve ser projetada como uma infra-estrutura distribuída de serviços de modo a oferecer acesso fácil e eficiente a estes. Neste trabalho, investigamos a possibilidade de se implementar tal infra-estrutura utilizando a arquitetura de objetos distribuídos OMG CORBA, a qual tem por objetivo facilitar a especificação, implementação e o acesso a interfaces de serviços de objetos distribuídos. Uma infra-estrutura de serviços de suporte a aplicações e de gerenciamento de cluster- é composta de dezenas de interfaces dos mais diversos tipos e finalidades, compondo vários sistemas e subsistemas distribuídos cujos serviços devem ser fácil e transparentemente acessíveis através da rede de comunicação que interconecta os nós do cluster. Essa rede tipicamente utiliza os protocolos de comunicação Ethernet IEEE 802.3, IP e TCP/UDP em seus níveis de enlace, rede e transporte, respectivamente. Por essa ótica, CORBA atende de antemão vários dos requisitos necessários, porém em diversos aspectos da arquitetura e dos serviços houve necessidade de se averiguar com mais profundidade a capacidade de CORBA de atendê-los. Como por exemplo, averiguou-se a capacidade de CORBA lidar com problemas ligados à falhas parciais de comunicação, comunicação em grupo, comunicação não-bloqueante e outras. Um dos desafios da abordagem utilizando CORBA reside no fato de que se tem o pré-requisito de alta disponibilidade. A arquitetura proposta deve ser projetada levando-se em conta que certas partes do sistema, tais como subsistemas de armazenamento, processamento, rede, aplicações e outros podem , a qualquer momento, falhar ou tornar-se inoperantes. O grande desafio deste trabalho consiste assim em averiguar quais são as dificuldades de se utilizar CORBA como parte central da arquitetura, uma vez que a infra-estrutura obtida necessita ser ela própria um conjunto de serviços de alta disponibilidade, caso contrário ela não conseguirá cumprir seus objetivos. Investigaremos então possíveis modos de implementação de objetos CORBA que venham a cumprir os requisitos de alta disponibilidade necessários. Por fim, este trabalho procura averiguar a possibilidade de se implementar tal arquitetura em clusters baseados em elementos de hardware e software disponíveis em larga escala e a baixo custo no mercado tais como PCs ou servidores baseados em processador Intel rodando os sistemas operacionais Linux ou FreeBSD e interconectados por redes locais de baixo custo. Tais plataformas são popularmente conhecidas como Beowulf Clusters. Este aspecto da investigação terá influência no projeto da arquitetura proposta, uma vez que procuramos enfocar aspectos de alta escalabilidade para o cluster, uma tendência para o uso desse tipo de cluster em aplicações de alta demanda de processamento e recursos, tais servidores web e de banco de dados de grandes provedores de conteúdo e serviços da Internet / This work intends to investigate for the difficulties and problems involved in the specification and implementation of an object-oriented architecture of services for management and support of distributed applications in a platform of computers in cluster configuration, in particular for those that must fulfill requirements of high availability. Such architecture must present itself as a infrastructure of distributed services and should compose an intermediate layer between the parts of the cluster distributed applications and the cluster resources, composing in this way a middleware layer. In order to reach its objectives, this support and management architecture must be designed as a distributed infrastructure of services. By this way, it can offer easy and efficient access to its services. In this text, we investigate the possibility of implementing such infrastructure of services using the distributed object architecture proposed by OMG, the so-called CORBA architecture. CORBA has many objectives and features as to facilitate the specification, implementation and access to distributed service objects. An infrastructure of services for the support and management of clusters and cluster applications is composed of a set of interfaces of the most diverse types and purposes, composing some distributed systems and subsystems whose services must be easy and transparently accessible through the communication networks that interconnects the cluster computer nodes. Cluster networks typically uses standard communication protocols such as Ethernet IEEE 802.3 at the data-link layer, the Internet Protocol (IP) at the network layer and TCP/UDP at the transport layer. In these aspects CORBA takes care on beforehand of severa1 of these requirements. However, for many service requirements of the proposed architecture it was necessary inquiring in more depth the CORBA capabilities to accomplish them. As an example, it was investigated the CORBA capabilities to deal with problems related to partial communication failures, communication for object groups, non-blocking and asynchronous communication and others. One of the challenges of the CORBA approach for the proposed architecture inhabits in the fact that the system must accomplish the prerequisite of high availability. The architecture proposal must be designed taking in account that certain parts of the system, such as storage subsystems, processors, network, applications and others can, at any time, fail or become inoperative. The great challenge of this proposal work consists thus inquiring the difficulties of adopting CORBA as a central part of the architecture, since the gotten infrastructure needss to be a proper high availability set of services. In contrary case, it will not fulfill its primary objectives. We will investigate possible ways of implementing CORBA objects in such a way that they fulfill the necessary high availability requirements. Finally, this work looks for the possibility of implementing the proposed system in clusters built with wide scale and low cost hardware and software elements available in the market, such as Intel-processor-based PCs and servers running open-source and low-cost operating systems such as Linux or FreeBSD and interconnected by low cost local area networks. Such platforms are popularly known as Beowulf Clusters. This aspect of The inquiry will have influence in the architecture proposal, once we are focusing aspects of high scalability for the cluster since there is a trend for the use of this type of cluster in applications of high demand of processing and resources, such as web servers for great suppliers of content and services on the Internet

Este trabalho procura averiguar as dificuldades e os problemas envolvidos na especificação e implementação de uma arquitetura de objetos de serviço para gerenciamento e suporte a aplicações distribuídas em uma plataforma de computadores em configuração tipo cluster, em particular daqueles que devem cumprir requisitos de alta disponibilidade. Tal arquitetura deve apresentar-se como uma infra-estrutura distribuída de serviços e compor uma camada intermediária entre as partes das aplicações distribuídas e os recursos do cluster, compondo desse modo uma camada de middleware. Uma arquitetura de gerenciamento e de suporte a aplicações distribuídas, para que possa atingir plenamente seus objetivos, deve ser projetada como uma infra-estrutura distribuída de serviços de modo a oferecer acesso fácil e eficiente a estes. Neste trabalho, investigamos a possibilidade de se implementar tal infra-estrutura utilizando a arquitetura de objetos distribuídos OMG CORBA, a qual tem por objetivo facilitar a especificação, implementação e o acesso a interfaces de serviços de objetos distribuídos. Uma infra-estrutura de serviços de suporte a aplicações e de gerenciamento de cluster- é composta de dezenas de interfaces dos mais diversos tipos e finalidades, compondo vários sistemas e subsistemas distribuídos cujos serviços devem ser fácil e transparentemente acessíveis através da rede de comunicação que interconecta os nós do cluster. Essa rede tipicamente utiliza os protocolos de comunicação Ethernet IEEE 802.3, IP e TCP/UDP em seus níveis de enlace, rede e transporte, respectivamente. Por essa ótica, CORBA atende de antemão vários dos requisitos necessários, porém em diversos aspectos da arquitetura e dos serviços houve necessidade de se averiguar com mais profundidade a capacidade de CORBA de atendê-los. Como por exemplo, averiguou-se a capacidade de CORBA lidar com problemas ligados à falhas parciais de comunicação, comunicação em grupo, comunicação não-bloqueante e outras. Um dos desafios da abordagem utilizando CORBA reside no fato de que se tem o pré-requisito de alta disponibilidade. A arquitetura proposta deve ser projetada levando-se em conta que certas partes do sistema, tais como subsistemas de armazenamento, processamento, rede, aplicações e outros podem , a qualquer momento, falhar ou tornar-se inoperantes. O grande desafio deste trabalho consiste assim em averiguar quais são as dificuldades de se utilizar CORBA como parte central da arquitetura, uma vez que a infra-estrutura obtida necessita ser ela própria um conjunto de serviços de alta disponibilidade, caso contrário ela não conseguirá cumprir seus objetivos. Investigaremos então possíveis modos de implementação de objetos CORBA que venham a cumprir os requisitos de alta disponibilidade necessários. Por fim, este trabalho procura averiguar a possibilidade de se implementar tal arquitetura em clusters baseados em elementos de hardware e software disponíveis em larga escala e a baixo custo no mercado tais como PCs ou servidores baseados em processador Intel rodando os sistemas operacionais Linux ou FreeBSD e interconectados por redes locais de baixo custo. Tais plataformas são popularmente conhecidas como Beowulf Clusters. Este aspecto da investigação terá influência no projeto da arquitetura proposta, uma vez que procuramos enfocar aspectos de alta escalabilidade para o cluster, uma tendência para o uso desse tipo de cluster em aplicações de alta demanda de processamento e recursos, tais servidores web e de banco de dados de grandes provedores de conteúdo e serviços da Internet / This work intends to investigate for the difficulties and problems involved in the specification and implementation of an object-oriented architecture of services for management and support of distributed applications in a platform of computers in cluster configuration, in particular for those that must fulfill requirements of high availability. Such architecture must present itself as a infrastructure of distributed services and should compose an intermediate layer between the parts of the cluster distributed applications and the cluster resources, composing in this way a middleware layer. In order to reach its objectives, this support and management architecture must be designed as a distributed infrastructure of services. By this way, it can offer easy and efficient access to its services. In this text, we investigate the possibility of implementing such infrastructure of services using the distributed object architecture proposed by OMG, the so-called CORBA architecture. CORBA has many objectives and features as to facilitate the specification, implementation and access to distributed service objects. An infrastructure of services for the support and management of clusters and cluster applications is composed of a set of interfaces of the most diverse types and purposes, composing some distributed systems and subsystems whose services must be easy and transparently accessible through the communication networks that interconnects the cluster computer nodes. Cluster networks typically uses standard communication protocols such as Ethernet IEEE 802.3 at the data-link layer, the Internet Protocol (IP) at the network layer and TCP/UDP at the transport layer. In these aspects CORBA takes care on beforehand of severa1 of these requirements. However, for many service requirements of the proposed architecture it was necessary inquiring in more depth the CORBA capabilities to accomplish them. As an example, it was investigated the CORBA capabilities to deal with problems related to partial communication failures, communication for object groups, non-blocking and asynchronous communication and others. One of the challenges of the CORBA approach for the proposed architecture inhabits in the fact that the system must accomplish the prerequisite of high availability. The architecture proposal must be designed taking in account that certain parts of the system, such as storage subsystems, processors, network, applications and others can, at any time, fail or become inoperative. The great challenge of this proposal work consists thus inquiring the difficulties of adopting CORBA as a central part of the architecture, since the gotten infrastructure needss to be a proper high availability set of services. In contrary case, it will not fulfill its primary objectives. We will investigate possible ways of implementing CORBA objects in such a way that they fulfill the necessary high availability requirements. Finally, this work looks for the possibility of implementing the proposed system in clusters built with wide scale and low cost hardware and software elements available in the market, such as Intel-processor-based PCs and servers running open-source and low-cost operating systems such as Linux or FreeBSD and interconnected by low cost local area networks. Such platforms are popularly known as Beowulf Clusters. This aspect of The inquiry will have influence in the architecture proposal, once we are focusing aspects of high scalability for the cluster since there is a trend for the use of this type of cluster in applications of high demand of processing and resources, such as web servers for great suppliers of content and services on the Internet

In order to meet the availability requirements of modern communication networks, a number of survivability techniques were developed that adapt the demand-wise shared protection design model to incorporate strategies increasing network availability. The survivability methodologies developed took two approaches. The first incorporated availability directly into the network design model. The second ensured minimum dual failure restorability was set within the model. These methodologies were developed for predetermined topologies, as well as to have topology optimization incorporated into the model. All methodologies were implemented and analyzed on a set of samples. The analysis examined cost, topology and actual availability of the network designs. Availability design was effective but computationally intensive and difficult to design. Minimum dual failure restorability was also effective in increasing availability with a significant caveat, dual failure restorability increased exposure to possible failures, and without sufficient levels of dual failure restorability could have a negative impact on availability. / Engineering Management

No description available.

Computer applications are no longer local installations on our computers. Many modern web applications and services rely on an internet connection to a centralized server to access the full functionality of the application. High availability architectures can be used to provide redundancy in case of failure to ensure customers always have access to the server. Due to the complexity of such systems and the need for stability, deployments are often avoided and new features and bug fixes cannot be delivered to the end user quickly. In this project, an automation system is proposed to allow for deployments to a high availability architecture while ensuring high availability. The purposed automation system is then tested in a controlled experiment to see if it can deliver what it promises. During low amounts of traffic, the deployment system showed it could make a deployment with a statistically insignificant change in error rate when compared to normal operations. Similar results were found during medium to high levels of traffic for successful deployments, but if the system had to recover from a failed deployment there was an increase in errors. However, the response time during the experiment showed that the system had a significant effect on the response time of the web application resulting in the availability being compromised in certain situations.