Maria Toeroe

Service Availability: Principles and Practice

Our society increasingly depends on computer-based systems; the number of applications deployed has increased dramatically in recent years and this trend is accelerating. Many of these applications are expected to provide their services continuously. The Service Availability Forum has recognized this need and developed a set of specifications to help software designers and developers to focus on the value added function of applications, leaving the availability management functions for the middleware. A practical and informative reference for the Service Availability Forum specifications, this book gives a cohesive explanation of the founding principles, motivation behind the design of the specifications, and the solutions, usage scenarios and limitations that a final system may have. Avoiding complex mathematical explanations, the book takes a pragmatic approach by discussing issues that are as close as possible to the daily software design/development by practitioners, and yet at a level that still takes in the overall picture. As a result, practitioners will be able to use the specifications as intended.

Generating AMF Configurations from Software Vendor Constraints and User Requirements

The Service Availability Forum (SAF) has defined a set of service API specifications addressing the growing need of commercial-off-the-shelf high availability solutions. Among these services, the Availability Management Framework (AMF) is the service responsible for managing the high availability of the application services by coordinating redundant application components. To achieve this task, an AMF implementation requires a specific logical view of the organization of the applications services and components known as an AMF configuration. Developing manually such a configuration is a complex, error prone, and time consuming task. In this paper, we present an approach for automatic generation of AMF configurations from a set of requirements given by the configuration designer and the description of the software as provided by the vendor. Our approach alleviates the need of configuration designers dealing with a large number of AMF entities and their relations.

Automatic generation of AMF compliant configurations

Service Availability Forum has defined a set of APIs to enable the building of off-the-shelf components for applications providing highly available services. A set of services has been defined and the Availability Management Framework is the service responsible of managing availability and therefore shifting this task from the applications to the middleware. Designing an AMF compliant configuration, for a given application, can be a tedious and error prone task because of the large number of attributes and parameters to be taken into account. In this paper, we propose an algorithm and the corresponding tool prototype for generating an AMF compliant configuration. We illustrate our approach with an example and discuss the main issues of the automatic generation.

Availability in the cloud

Availability is a non-functional requirement defined as the percentage of time a system or a service is accessible. This percentage determines the acceptable total outage time for any given period. High-Availability (HA) is a stringent requirement which allows for a maximum of approximately five minutes downtime in a year including outage due to scheduled maintenance and upgrades. It is agreed that availability is among the main challenges of the cloud. There has been a lot of work on availability in cloud computing, but cloud providers and researchers from the academia and the industry have used different definitions for availability and the related concepts. Thus, it is difficult to evaluate and compare different solutions. In this paper, we present a survey of availability solutions proposed for the cloud by the main cloud providers and by 21 most relevant conference and journal papers out of the 100 papers collected initially. To conduct this survey we defined a taxonomy, which captured the main concepts, mechanisms and metrics for availability. We use this taxonomy to evaluate and classify the solutions of cloud providers as well as solutions proposed in research papers, their strengths and weaknesses. We point out potential future research directions.

A UML-Based Domain Specific Modeling Language for the Availability Management Framework

The Service Availability Forum (SA Forum) is a consortium of several telecommunications and computing companies that defines standard solutions for high availability platforms. One of the most important SA Forum services is the Availability Management Framework (AMF) which is responsible for managing the availability of an application running under its control. To achieve this, AMF requires a complete configuration, which consists of several entities organized according to AMF rules and constraints. In this paper, we argue that AMF concepts form a domain for which a domain-specific modeling language can greatly facilitate the generation, analysis and the management of AMF configurations. We define such a language by extending UML through its profiling mechanism and we implement it. More important, we discuss the challenges and the lessons learned in the course of this project.

Integrating Legacy Applications for High Availability: A Case Study

Service high availability is becoming a must in various domains. Services provided by applications originally not designed for high availability can be rendered highly available by integrating them with a middleware compliant to the SAForum specification. Such a middleware offers a number of configuration options. The assessment of service availability at the design of the system configuration facilitates the selection of a system configuration, which is optimal with respect to specific priorities. In this paper we present a case study of turning a legacy video streaming application into a highly available one. We present our methodology, and then we analyze the availability we can expect from the application in various configurations and settings.

Providing Hardware Redundancy for Highly Available Services in Virtualized Environments

High-Availability requires hardware and software redundancy. Virtualization is a technique - among others - for improving the utilization of hardware resources by making virtual (rather than actual) versions of hardware, operating system, etc. and collocating them on the same hardware. In virtualized environments virtual machines (VMs) are used for the deployment of the software entities. When VMs hosting redundant software entities providing and protecting some service are collocated on the same physical node, the hardware redundancy is lost and the failure of this physical node certainly leads to service outage. To achieve high availability, we need to avoid such single points of failure even in the presence of VM migration. This paper tackles this issue in the context of a standardized middleware for service high-availability.

SDL 2013: Model-Driven Dependability Engineering

In this paper, we present how we created a Domain Specific Language (DSL) dedicated to IP Multimedia Subsystem (IMS) at Ericsson. First, we introduce IMS and how developers are burdened by its complexity when integrating it in their application. Then we describe the principles we followed to create our new IMS DSL from its core in the Scala language to its syntax. We then present how we integrated it in two existing projects and show how it can save time for developers and how readable the syntax of the IMS DSL is.

A Tool Suite for the Generation and Validation of Configurations for Software Availability

The Availability Management Framework (AMF) is a service responsible for managing the availability of services provided by applications that run under its control. Standardized by the Service Availability Forum (SAF), AMF requires for its operations a complete and compliant AMF configuration of the applications to be managed. In this paper, we describe two complementary and integrated tools for AMF configurations generation and validation. Indeed, writing manually an AMF configuration is a tedious and error prone task as a large number of requirements defined in the standard have to be taken into consideration during the process. One solution for ensuring compliance with the standard is the validation of the configurations against all the AMF requirements. For this, we have designed and implemented a domain model for AMF configurations and use it as a basis for an AMF configuration validator. To further ease the task of a configuration designer, we have devised and implemented a method for generating automatically AMF configurations.

Managing application level elasticity and availability

Elasticity and availability are two features associated with the cloud. Existing solutions focus on providing both at the level of the virtual infrastructure through virtual machines (VMs), their restart, addition, and removal as needed. These assume a specific application design paradigm, which equates the application and its workload to the VM. High-availability applications are typically composed of redundant components that recover from failures through state-full failover orchestrated by a middleware (MW). For such applications handling elasticity purely through addition and removal of VMs is not sufficient, the application level also needs to be considered. This requires solutions that coordinate the availability and elasticity management at the application level. In this paper we propose a solution in the context of the Service Availability Forum (SAF) defined MW. It manages the application level elasticity through the manipulation of the application configuration used by the MW to ensure service availability. This in turn triggers the MW to change the workload distribution in the system.