There are four best practice areas for reliability in the cloud:

Amazon CloudWatch is a monitoring and observability service that provides you with data and actionable insights to monitor your workload, respond to system-wide performance changes, optimize resource utilization, and get a unified view of operational health.

The AWS service that is essential to reliability is Amazon CloudWatch. Amazon CloudWatch monitors the Amazon Web Services (AWS) resources and the applications we run on AWS in real time. We can use CloudWatch to collect and track metrics, which are variables we can measure for the resources and applications.

• Foundations.
• Workload Architecture.
• Change Management.
• Failure Management.

Amazon EC2 Reliability The Amazon Elastic Compute Cloud service level agreement guarantees customers a 99.99% uptime for EC2 instances during a given month. If this uptime is not met, the amazon customer will receive credits for any amount of uptime lower than this amount.

If you are running instances on Amazon EC2, Amazon provides several built-in capabilities to achieve high availability:

1. Elastic Load Balancing—you can launch several EC2 instances and distribute traffic between them.
2. Availability Zones—you can place instances in different AZs.

Answer. Load balancer and Auto scaling are the two services which will help in better availability.

Amazon S3 is an object storage service that provides highly durable, secure, fault-tolerant data storage. AWS is responsible for maintaining availability and fault-tolerance; you simply pay for the storage that you use.

High Availability (HA) describes systems that are dependable enough to operate continuously without failing. They are well-tested and sometimes equipped with redundant components. High availability refers to those systems that offer a high level of operational performance and quality over a relevant time period.

Five-nines or 99.999% availability means 5 minutes, 15 seconds or less of downtime in a year. Or, if you are really ambitious, shoot for six nines or 99.9999% availability, which allows 32 seconds or less downtime per year.

Companies aiming for high availability (HA) talk about four nines (less than an hour of downtime a year), which is what we strived for during my time at Netflix. Five nines availability, which means only five minutes of downtime per year, is ambitious.

99.999%

4.38 minutes downtime per month

Uptime is the amount of time that a service is available and operational. Uptime is generally the most important metric for a website, online service or web based provider and is expressed as a percentage such as ‘99.9%’. For example a 99.9% uptime equates to 43 minutes and 50 seconds of downtime.

3 Types of Service Level Agreements

• Customer-based SLA. This type of agreement is used for individual customers and comprises all relevant services that a client may need, while leveraging only one contract.
• Service-based SLA. This SLA is a contract that includes one identical type of service for all of its customers.
• Multi-level SLA.

Percentage calculation

The accepted availability standard for emergency response systems is 99.999% or “five nines” – or about five minutes and 15 seconds of downtime per year (see table below). To achieve five nines, all components of the system must work seamlessly together.

Identify dependencies

Availability = Uptime ÷ (Uptime + downtime) That equals 10 hours of total downtime.

Some of the key differences between High Availability and Disaster Recovery are: High Availability uses redundancy in the system to overcome any component failure whereas Disaster Recovery uses an alternate site or cloud services to restore normal or near normal function of the entire production system.

SQL Server high availability (HA) is about providing service availability and 100% uptime through redundant and fault-tolerant components at the same location. Disaster Recovery (DR) is about providing service continuity and minimizing downtime through redundant & independent site in a distinct location.

High availability means that the systems will always be available regardless of what happens. With redundancy, you may have to flip a switch to move from one server to the other, or you may have to power up a new system to be able to have that system available.

Here are some of the key resources you can implement to make high availability possible:

1. Implement multiple application servers.
2. Scaling and slaves matters.
3. Spread out physically.
4. Maintain a recurring online backup system along with hardware.
5. Use of a virtualized server for zero-downtime recovery.

Why do system administrators consider using failover strategies? Scalability is the ability to improve the performance of a server without diminishing its usefulness or increasing its cost disproportionately. A clustered server environment can be configured with as few as ____computers.

The Importance of High Availability By using best practices designed to ensure high availability, you help your organization achieve maximum productivity and reliability. With a high availability strategy in place, you reduce the negative impacts of downtime and implement automatic recovery from system failures.