Introduction
Technological resilience is essential for ensuring uninterrupted service delivery in today’s digital landscape, especially those mission-critical systems. One prime measure of such resilience is High Availability (HA). Achieving HA can often be complex, but with the right strategies and tools, it is highly attainable. In this article, we delve into the fundamentals of high availability, its workings, and how OpenClovis SAFplus aids in achieving it.
Overview
High Availability (HA) is used when referring to a system that is capable of providing service “most of the time.” High availability can be achieved by combining many different design concepts and system characteristics, including hardware and software level redundancy, fault detection capabilities, component failover, fault isolation, fault recovery, alarm notification, and so on.
Key HA Concepts
Availability is a measure of the probability that a service is available for use at any given instant. It allows service failure, with the assumption that the service restoration is imminent. The key to high availability is to continue the service without significant interruption.
The five key system characteristics contributing to HA are:
- Failure detection: how reliably and quickly can failure be detected
- Failure notification: how reliably and quickly can the information of the failure be passed to an authority that can decide how to handle the failure
- Response time: how long it takes for the failure handling authority to process the information about the failure and come to a decision on how to best handle the failure
- Repair/replacement time: how long it takes to repair or replace the failed component
- Recovery/restart/reboot time: how long it takes to restore the original system state and hence restore the service.
How does High Availability Work?
HA works by eliminating single points of failure within a system and implementing mechanisms for fault detection, automatic failover, and redundancy. Here’s how it typically functions:
- Redundancy: Duplicate components (servers, storage, network links) are maintained to ensure that failure of a single component does not disrupt the service.
- Failover Mechanisms: Automatic processes detect failures and switch operations to standby components without human intervention.
- Load Balancing: Distributes workloads across multiple servers or nodes to ensure no single component is overwhelmed and to minimize downtime.
- Data Replication: Copies data across multiple nodes or locations to ensure it is always available and can be quickly restored in case of any failures.
Importance of High Availability
High availability is crucial for several reasons:
- Business Continuity: Minimizes the impact of failures on operations, maintaining the seamless availability of services and applications.
- Customer Trust: Consistent reliability enhances customer satisfaction and loyalty.
- Regulatory Compliance: Certain industries require adherence to stringent availability standards to ensure data integrity and availability.
- Financial Impact: Reduces potential financial losses associated with downtime, such as lost sales in e-commerce or missed transactions in banking.
What is High Availability across clusters?
High availability across clusters is a group of servers working together to ensure that service remains available even if one or more servers fail. Components of an HA cluster include:
- Primary and Standby Nodes: The primary node handles active workloads, while standby nodes remain ready to take over if the primary node fails.
- Heartbeat Mechanisms: Regular checks between nodes to ensure system health and initiate failover if a failure is detected.
- Shared Storage: Storage accessible by all nodes to ensure data consistency and availability across the cluster.
- Cluster Management Software: Tools like Pacemaker and Corosync manage the nodes, detect failures, and coordinate failover processes.
Some fields can apply High Availability
High Availability can be applied to variety of fields, including
- Networking and telecommunications
- Defense
- Data center
- Financial Markets Trading Systems
- Banking systems
- Medical and Health care
- Industrial manufacturing
- Gaming servers
- Enterprise
- Air traffic control systems
- And a lot more…
How does OpenClovis help achieve High Availability
OpenClovis SAFplus Platform provides infrastructure for the end-to-end life-cycle of failure handling, including failure detection, to policy-based recovery decision making, through failover and fault repair operations. However, for custom software applications to be able to quickly fail over without major disturbance to the rest of the system, the applications themselves need to exhibit some special characteristics. These include:
- Capability to move state data and context among redundant components
- Move the service from one component to another in a way that the failover is transparent to the rest of the system
In addition to the above mentioned end-to-end failure handling, OpenClovis SAFplus Platform provides additional services to allow application programmers to implement the above characteristics. These include checkpoint service (to save, pass, and restore system state) and location-transparent addressing (to hide the failover from other components).
Redundant components providing the same service can be arranged in many relationships. The most common arrangements are:
- 2N (1+1) redundancy: for every active component there is exactly one standby component
- M+N redundancy: for every M active components there are N standby components, any of which is ready to take over the service from any of the active components. (Note that 1+1 is merely a special, but most common, case of M+N.)
Conclusion
High availability is a critical aspect of modern database management, ensuring that services remain uninterrupted and resilient in the face of failures. By understanding HA’s principles and implementing best practices, organizations can significantly enhance their service reliability. OpenClovis provides a robust solution for achieving HA through its distributed architecture, automated failover capabilities, and seamless scalability. These features make OpenClovis an excellent choice for businesses aiming to offer relentless service availability and superior performance.
Other support, please send email to support@openclovis.org.