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Using Xervmon for planning and provisioning redundancy across multiple availability zones The cost of downtime Downtime costs enterprises money, in fact a great deal of money. The actual cost depends on the industry, but on average the revenue losses amount to between $84,000 and $108,000 for every hour of unplanned downtime. That isn’t the only loss; on to that you need to add the intangible costs of the impact of downtime on reputation and loyalty. Managing downtime There is a big difference between scheduled and unscheduled downtime. Scheduled downtime is necessary in order to perform maintenance such as software patches, system configuration changes and database and hardware maintenance. Unscheduled downtime occurs typically as the result of hardware or software failure or an event such as a power cut or environmental catastrophe. High availability Designing a system for high availability is problematic. Increasing system complexity increases the number of possible failure points. Simply installing internal hardware redundancy isn’t an answer as it means that the whole system must be taken down for maintenance. It is necessary so design the system so that it can be maintained without affecting service availability. Such a management tool needs to satisfy three criteria: high availability, fault tolerance and scalability. High availability implies that the uptime of an application is 99.9999%, which is often termed â€Å"five nines†. It equates to a maximum downtime of 5.26 minutes a year which includes both planned and unplanned outages or downtime. Of course the ultimate goal is an application that has no downtime at all and is always available. Xervmon Solution: Users can now unleash the power of visualized deployments with ... ... have been restored. ELB and Auto Scaling combine ideally: ELB gives a single DNS name for addressing and auto scaling ensures there is always the right number of healthy Amazon EC2 instances to accept requests. Fault Tolerance Building fault-tolerant applications on Amazon EC2 requires that the best practices are followed, for instance: †¢ Commission replacement instances rapidly †¢ Amazon EBS should be used for persistent storage †¢ Multiple Availability Zones along with elastic IP addresses. Multi AZ architecture By distributing applications geographically one can achieve greater fault tolerance. As the Amazon EC2 commitment is 99.95% availability for every EC2 Region, it is essential to deploy applications across multiple AZs. Redundant instances are placed in distinct AZs and ELB will automatically balance traffic across multiple instances and multiple AZs.