A Quick-Start Guide to AWS High Availability and Its 3 Dimensions

Fault tolerance is now considered a must, not a feature, according to the general consensus. Businesses must now run their apps or services 24×7, in order to meet customer and stakeholder expectations. Failure to do so results in unavailability, which frustrates customers. This leads to a loss of customer satisfaction, which eventually leads to a loss of revenue. 

The Amazon Web Services (AWS) has become a ubiquitous cloud platform with more than 200 fully-featured services like AWS EC2, AWS Lambda, S3, DynamoDB, and RDS and million-plus active users. The AWS platform is unique in building fault-tolerant business applications since AWS high availability delivers features that let you build these fault-tolerant applications with little interaction and minimal investment.

This guide takes you through the concepts of AWS high availability. We discuss the fundaments of AWS, AWS high availability architecture, advantages, as well as a detailed analysis of AWS computing, database, and storage dimensions.

What Is High Availability?

No business wants failures in its operational systems. Failures create downtime, which is a period of time when your system is not available for use or is unresponsive. Downtime hampers business output and performance. For big corporations, each minute of downtime costs thousands of dollars. Into the bargain, they bring unnecessary maintenance costs, which are sometimes too costly to implement.

High availability (HA) is a system’s ability to function even when some components fail. High availability guarantees continuous operability of systems for desirably long periods of time. A solid requirement for enterprises, high availability protects businesses against the risks brought by a system outage. 

High availability for systems is represented through a sequence of “9’s”. A 100% availability translates to 0 minutes of downtime in a year, which is practically infeasible and an ideal benchmark. A three-nines availability, represented as 99.9%, allows 8 hours and 46 minutes of downtime per year. A four nine availability, 99.99%, allows 52 minutes and 36 seconds downtime per year, and a five-nine availability, which is the accepted standard for emergency response systems and mission-critical operations, provides about 5 minutes and 15 seconds of downtime per year.

Advantages of Using AWS High Availability for Web Applications

AWS high availability for web applications provides you with the following benefits:

• A completely secured network that uses a Web Application Firewall (WAF) to prevent common web exploits.
• AWS HA has provisions like Business Continuity (BC) and Disaster Recovery (DR) technologies to help businesses resume operations with minimal disruption.
• For cases where instant hardware failure may arise or are about to arise, AWS Auto Scaling automatically detects this and launches a new instance.
• AWS HA provides metrics on the cloud to closely monitor the application based on the number of users using the application or the memory consumed by the particular instance.
• The deployment of new features or updates may be done without causing any problems for present users.

AWS Regions and High Availability Zones

• Amazon hosts its web services across multiple locations, with each AWS location consisting of multiple availability zones and availability ranging from 99.9% to 99.999%. 
• Each AWS Region runs in complete autonomy. This ensures the greatest level of fault tolerance and stability for user and application workloads. 
• All AWS Availability Zones (AZs) are configured to operate in such a way that they are able to provide inexpensive, low latency network connectivity to other Availability Zones in the same region as well. These are connected to multiple Internet Service Providers (ISPs) and different power grids.
• Your application(s) can be safeguarded against failure in a single data center by deploying EC2 instances in various Availability Zones.
• It is important to run independent application stacks in more than one Availability Zone, either in the same region or in another region, so that if one zone fails, the application in the other zone can continue to run. 

To know about Amazon Regions and Availability Zones in your area, visit Regions and AZs.

AWS Services Used to Achieve High Availability

AWS delivers high availability through a scalable, load-balanced cluster or an active-standby pair, among other approaches. The majority of Amazon Web Services are designed to be fault-tolerant and have high availability. The following list includes some of them:

• Amazon S3
• SimpleDB
• Amazon Relational Database (RDS)
• Amazon Simple Queue Service (SQS)
• Elastic Load Balancing (ELB)
• Amazon Simple Notification Service (SNS)
• Amazon Virtual Private Cloud (VPC)
• Amazon Machine Engine (AMI)

AWS Fault-Tolerant and High Availability Architecture

Here’s a high-level diagram of how different AWS services combine together to provide a fault-tolerant and high availability architecture on the cloud.

AWS High Availability: Compute, Databases, and Storage

AWS offers emergency response systems and high availability resilient systems in the cloud to best cater to user needs. It comes across three different dimensions:

1. Compute: Compute dimension contains AWS services like Amazon EC2 and AWS Lambda that provide AWS HA features such as load balancing, auto-scaling, and provisioning across Amazon Availability Zones (AZ).
2. SQL Databases: Amazon RDS and other managed SQL databases provide RDS high availability options for automatically deploying databases with a standby replica in a different Availability Zone.
3. Storage Services: Amazon storage services, such as S3, EFS, and EBS, provide built-in high availability options. S3 and EFS automatically store data across different Availability Zones, while EBS enables the deployment of snapshots to different Availability Zones.

In the sections that follow, we’ll look more closely at the aforementioned dimensions and how AWS high availability may be applied to them.

AWS High Availability for EC2 Instances

Amazon EC2 lets you achieve a reasonably good level of high availability and resilience by using an Elastic Load Balancer, Auto Scaled AWS Environment, and Availability Zones built into the database cluster. The description of these components is as follows:

• Elastic Load Balancing allows you to launch several EC2 instances and spread traffic judiciously between them.
• Availability Zones allow you to distribute EC2 instances across many locations, reducing the risk of a single point of failure.
• Auto Scaling detects load increase and dynamically adds new instances.

To reap the benefits of high availability in Amazon EC2, it is recommended that you run EC2 instances in multiple Availability Zones (AZs). In case one of these zones becomes unavailable due to natural circumstances or power outage, Elastic Load Balancer can reroute traffic to operational AZ. At the same time, Auto Scaling automatically increases the number of instances to meet your high traffic demands. This can be understood from the figure displayed below.

AWS High Availability for SQL Databases on Amazon RDS

Amazon Relational Database Service is a collection of Managed Relational Database Services (RDBMS) running on the cloud. This functionality creates a fast & consistent input & output performance, and AWS RDS high availability for different database engines like MySQL, AWS Aurora, Oracle Database, MariaDB, PostgreSQL, and SQL Server. 

To achieve RDS high availability, Amazon supports two easy-to-use options.

• Amazon RDS Multi-AZ Deployments: In Multi-AZ deployments, Amazon RDS automatically generates a primary DB instance and synchronously replicates the data to a standby instance in a separate Availability Zone. This deployment is applicable for MySQL, MariaDB, PostgreSQL, Oracle, and SQL Server database (DB) instances.
  
  In the event of an infrastructure failure, Amazon RDS automatically switches to the backup database instance. Your application may restart the database function without the requirement for human administrative intervention because the endpoint for your DB instance stays the same after a failover.

• Multi-AZ Failover For Amazon Aurora Cluster: By duplicating your data six times across three Availability Zones, Amazon Aurora for PostgreSQL and MySQL engines boost availability. This implies that a failure of an Availability Zone in your DB cluster will result in no data loss and just a temporary service outage.
  
  You also have the option of running one or more Replicas in an Amazon Aurora DB cluster. RDS automatically promotes an existing Aurora Replica to be the new primary instance and changes the server endpoint if the primary instance in the DB cluster fails, so your application may continue to run without any manual involvement.
  
  When a problem is identified and no Replicas have been deployed, RDS will immediately generate a new replacement DB instance for you, hence delivering AWS RDS high availability for all your needs.

More:

• Amazon RDS MySQL Integration: 3 Easy Steps
• RDS Oracle PostgreSQL Integration: 2 Easy Methods

AWS High Availability for Storage Services

The last dimension of our AWS high availability guide is storage services. Amazon Storage Services comprise reliable, scalable, and secure cloud storage services like Amazon Simple Storage Service (S3), Amazon Elastic File System (EFS), Amazon FSx, and Amazon Elastic Book Store (EBS).

• Amazon Simple Storage Services (S3) is an AWS Object Storage Solution offering secure, durable, and scalable object storage for IT teams and developers. Amazon S3’s standard storage offers 99.99% availability for object storage with 99.999999999% durability.
• Amazon Elastic File Storage (EFS) provides a managed file storage solution for NFS file systems on Linux. EFS offers a Service Level Agreement of four-nine availability (99.99%), otherwise between 10-100% of the service fee is discounted.
• Amazon Elastic Block Store (EBS) is a block storage service that is designed to work with Amazon EC2 instances and is highly scalable and high-performing. At any size, it can manage high-throughput and transaction-intensive applications. You can create an EBS volume in another Availability Zone and attach it to additional instances in that Availability Zone. You may also take snapshots and restore them in a different Availability Zone within the same area.
• Amazon FSx is a feature-rich, high-performance file system in the cloud. Amazon FSx protects your data against component failure by automatically replicating it inside or across AWS Availability Zones, continually monitoring for hardware faults, and immediately replacing infrastructure components or switching to a stand-by file server in the case of a failure.

Conclusion

To recapitulate, this blog introduced you to the fault-tolerant systems of AWS. You learned about the diverse array of AWS services in three different dimensions: compute, database, and storage. These solutions help you to avoid degradation and points of failure. AWS high availability and low-cost implementations involve minimal human intervention and low up-front financial investments, which makes AWS the best option for building your fault-tolerant software systems.

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Have any questions on AWS high availability components? Do let us know in the comment section below. Also, share any other AWS high availability services or features you’d want us to cover. We’d be happy to know your opinions.