AWS WAF pillar three: Reliability tools and best practices

Harnessing the full power of the AWS® cloud involves far more than building a solid technical infrastructure. Amazon developed the Well-Architected Framework (WAF) to enable companies to build the most operationally excellent, secure, reliable, efficiently high-performing, and cost-optimized infrastructure possible for their businesses. This post addresses the third pillar, reliability.

What is the WAF reliability pillar?

The AWS WAF provides a consistent review and measurement process for cloud architects, by using AWS best practices. As one of the five pillars of the AWS WAF, reliability is a key focus of framework best practices.

Infrastructure reliability means different things to different people but is defined as “the ability of a system to recover from infrastructure or service disruptions, dynamically acquire computing resources to meet demand, and mitigate disruptions such as misconfigurations or transient network issues.” Of course, uptime is a critical metric for network reliability.

The WAF reliability pillar: AWS tools and best practices

The WAF reliability pillar emphasizes three areas of concern: Foundations, Change Management, and Failure Management. This post summarizes a more detailed AWS document, Reliability Pillar: Well-Architected Framework, examines each area, and reviews the AWS tools and best practices that you can use to address each one.


The Foundations best practices for AWS involve reliability issues that you should understand before you architect the system. This includes limit management, network topology planning, and monitoring.

  1. Limit management: Limit management addresses your network architecture’s physical limitations and resource constraints. Physical limitations include issues such as ensuring that your AWS instances provide the bandwidth and storage capacity that you need both now and in the future. AWS has soft limits like the number of requests, the number of EC2 instances, and the number of EBS volumes. You can change these, but you might need permission. However, you can’t change hard limits like the number of security groups and the number of rules in the security groups. Use the free AWS Trusted Advisor checks to test the adequacy of your architecture for performance, service limits, and security groups. AWS recommends that you track limits by storing them in DynamoBD or integrating your Configuration Management Database with AWS Support APIs and setting alarms for limits tracked by CloudWatch®.

  2. Network topology planning: Topology planning addresses planning for future growth in terms of the number of IP addresses you need and the systems and networks you might need to integrate with. You also need to plan for resilienc—for possible failures, misconfigurations, attacks, and unexpected increases in traffic or service use. As a best practice for IP addresses, use Amazon® Virtual Private Cloud (Amazon VPC) to allocate private address ranges, as identified by RFC 1918, for your VPC Classless Inter-Domain Routing blocks. These addresses either provide non-Internet accessible resources or to extend your data center. For resiliency, best practices are to make sure connections to the data centers are redundant and that you have a subnet or set of subnets for each Availability Zone to serve as a barrier between the Internet and your applications. AWS also has many attack protection services, such as Web Application Firewalls, to deflect common attacks.

  3. Monitoring: You can manage what you can’t measure, and monitoring is critical for effective change management. AWS has customizable hooks and visibility into everything from instance performance to network layers, down to request APIs themselves. Identify what services and applications you want to monitor, define the metrics you are concerned about, and learn how to access logs for these metrics from AWS products and features. The key AWS service that supports monitoring is Amazon CloudWatch, which easily allows you to create alarms automatically to trigger scaling actions automatically.

Change management

Planning for network changes is another foundation of the AWS Reliability Pillar, which includes changes in demand and monitoring and executing changes.

  1. Changes in demand: Often, when demand spikes, you become aware of some architectural defects, just when you need them least! The best way to avoid scalability issues is to test your implementation rigorously against as-close-to-real conditions as possible. Using AWS Auto Scaling is the best practice to automate instance replication. You can use Auto Scaling groups for specific resource types and use CloudWatch to set scaling triggers.

  2. Monitor and execute changes: Change execution in the cloud is a matter of software development. In an infrastructure-as-code environment, you can describe infrastructure changes as differences between running environments and objects that exist in source control. Set up development, test, and production environments that allow you to test your changes before deploying them. You can also test complete deployments with all the bells and whistles in your production environment—networks, firewalls, data transmission, and so on. The key tool that enables infrastructure-as-code is AWS CloudFormation®. You can deploy any part of your infrastructure and applications as distinct CloudFormation stacks.

Failure management

Failure management recognizes that failures will happen. It is critical to know how to identify, respond, and prevent future failures. AWS WAF breaks failure management into three parts: data durability, withstanding component failures, and planning for recovery.

  1. Data durability: The loss of data is one of those things that keeps most IT leaders up at night. As a general best practice, define a recovery point objective (RPO)—a threshold of loss time that constitutes an incident—and a recovery time objective—is the amount of time it takes to restore data. AWS recommends regularly testing backup and restore capabilities to define these thresholds and set policies accordingly. The key AWS service supporting durability is S3® storage. With 99.999999999 percent reliability, S3 provides near perfect data durability.

  2. Withstanding component failure: Load sharing is the primary means of eliminating single points of failure that can damage or lose data. In the cloud, Mean Time To Recover (MTTR) is more important than Mean Time Between Failure (MTBF) because you can automate recovery based on calculated recovery times. AWS can automatically take action and notify appropriate personnel. A WAF best practice is to design your infrastructure such that your systems are decoupled, thus avoiding a domino-effect of cascading failures. AWS offers multiple load sharing tools, including Availability Zones in multiple AWS Regions, Elastic Load Balancer, Application Load Balancers, and S3 storage. As an AWS best practice, use AWS SDKs to test components to withstand failure and determine failure and recovery thresholds.

  3. Planning for recovery: Expect the unexpected might be the watchword for AWS failure management. It is critical to know what to do in the event of a serious system, service, or component failure. Critical AWS best practices include testing for resiliency, performing multiple disaster recovery drills until responding becomes second-nature, keeping all versions of the network in sync, and using Availability Zones so that you can shift operations to a working site to avoid business disruptions. The key AWS service for recovery planning is AWS Identity and Access Management, which you can use to grant access to those who need it if disaster strikes. Taking regular backups on S3 is also critical, as is the ability to automate the delivery of all systems to another AWS Region or account.


The good news is that AWS has been proven to be more reliable than data centers when it comes to change and failure management. As Richard Cowley, Director of Operations at Slack® has said, “AWS does a much better job at security than we could ever do running a cage in a data center.” Follow these best practices to ensure your infrastructure is as reliable and resilient as possible.

Learn more about the other Well-Architected Framework pillars in this series:

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Rackspace Onica Team

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