AWS Reliability Pillar: 5 Essential Design Principles

From a cloud computing perspective, optimizing the AWS reliability pillar isn’t about ensuring your systems run 24/7. No system, no matter how well designed, can guarantee zero failure. Then what separates a reliable system from a fragile one? It is not the absence of failure. But the ability to respond to failure without collapsing.

The reliability pillar ensures a system detects failure and mitigates disruptions, including misconfigurations and network issues, through automated recovery. Detecting failures without human intervention minimizes downtime and operational burden and improves service predictability.

We have covered AWS best practices in-depth to help you understand architectural decisions through our AWS Well-Architected Framework pillar series. Follow the links to catch up. Pillar Operational Excellence Pillar 2: Security.

What defines cloud reliability?

Organizations can view cloud reliability from different perspectives. That is one of the key takeaways of the reliability pillar. As an organization, team, or department, you set the KPIs and measure the system’s reliability based on specific business requirements and objectives.

That said, several factors should be focused on when following the guidelines of the reliability pillar. The most crucial factor is system or service availability. Availability is the uptime in the AWS Service Level Agreement, calculated annually. A 99% availability means there must not be more than three hours and 15 minutes of disruption every year. A 99.99% availability, on the other hand, brings that number all the way to 52 minutes. Availability for different application categories varies.

For real-time applications such as point-of-sale and e-commerce sites, 99.95% availability is the recommended level. For ATMs and more advanced use cases, hitting the 99.99% mark is the goal. Sometimes, cloud engineers must strive for 99.999% availability to achieve the desired standard.

Goal of the reliability pillar

Apart from monitoring, alerting, and recovering from failure, the goal of the reliability pillar of the AWS Well-Architected Review is to test failure modes, change management, and demand forecasting. Here is a detailed breakdown.

1. Test failure modes: AWS treats the reliability pillar as a measurable engineering discipline, not just an aspiration. Architects anticipate how systems might fail, such as an instance crash, an availability zone failure, or service degradation.
   
   Why it matters: If you don’t know how systems behave under failure, you cannot build resilience. Architectural designs often look good on paper but fail in unpredictable ways. Concepts like chaos engineering help understand those weaknesses, proving systems can recover from unforeseen scenarios.

2. Adjust to varying demands: The reliability pillar ensures the cloud is architected to handle unexpected spikes, such as a product launch or viral event.
   
   Why it matters: Static or poorly forecasted capacity planning leads to over-provisioning or under-provisioning. That can be a common failure point in cloud-native workloads, especially when demand is highly variable.
    

   

3. Dependency tracking: Reliability isn’t just about what you build but also about what you depend on—third-party APIs, external systems, and managed services. Architects must analyze single points of failure in external integrations, model their SLAs, and incorporate fallbacks or retries.

Why it matters: You can’t control third-party services, but you can control how much damage they cause when they fail. Failing to do so can result in cascading failures.

4. Change management: Change is one of the most common root causes of system failure. Therefore, change management must be frequent, automated, and low-risk.

Why it matters: Systems with poor change discipline often experience configuration drift, broken dependencies, or regression bugs. Frequent, automated changes reduce blast radius and help identify issues early.

5 design principles of the reliability pillar

The main objective of the reliability pillar is to support the systems it hosts sustainably. One that can deal with disruptions and failures effectively. It means there are certain parts of the cloud environment and the policies around them that must follow the basic design principles of this pillar, which are:

• Test recovery procedures:  The risks cloud environments and systems face, the points of failure for systems and ecosystems, and details about the most probable attacks can be predicted and simulated. Organizations can test recovery procedures based on insights. In this case, exploiting fundamental points of failure and how the environment reacts to the emergency shows how reliable the system is.
• Automatic recovery from failure: Once again, automation – one of the strong suits of Amazon Web Services – plays a vital role in keeping an AWS environment reliable. Using logs and metrics from CloudWatch and designing a system where failures trigger recovery is the way to move forward.
• Scale horizontally to increase aggregate system availability: In other words, the cloud environment needs to have multiple redundancies and additional modules as added security measures. Of course, various redundancies require good management and maintenance to remain active throughout the environment’s lifecycle.
• Stop guessing capacity: The use of resources is monitored not just for cost-efficiency, but to allow the environment to stay optimum at all times. Having enough resources to deal with spikes in traffic or requests, combined with clear policies and automation, means the AWS environment always has the resources needed by the systems running in it. Scaling up (and scaling back down if required) is equally easy.
• Use automation to handle changes: Once again, the six pillars take into account human error as a prominent cause of issues and suggest the use of codes and automation to simplify processes like upgrading, adding new EC2 computing power, and bringing in more cloud storage space to the environment.

Building high availability in the cloud

High Availability (HA) is a subset of reliability. It focuses on ensuring that a system is accessible and operational at all times, typically measured as a percentage uptime (e.g., 99.99%). AWS Trusted Advisor and the AWS Management Console give you access to information about the system, resource usage, and usage patterns. Gathering these details takes a short time, but they are valuable if you are serious about designing a highly available app.

High availability is not just jargon. Creating and maintaining a highly available environment requires using capable AWS instances and supporting services such as EC2, good monitoring tools – including the Amazon CloudWatch – and Elastic Load Balancing. It is also necessary to introduce multiple redundancies across the environment. But that doesn’t mean it is not doable. More importantly, a highly available environment is worth pursuing for its benefits in return and the boost in user experience delivered in the process. With this article’s design principles and guidelines, you can establish the reliability pillar for your cloud environment.

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