The Reliability pillar includes 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

The reliability pillar provides an overview of design principles, best practices, and questions. You can find prescriptive guidance on implementation in the Reliability Pillar whitepaper.

Design Principles

There are five design principles for reliability in the cloud:


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

To achieve reliability, a system must have a well-planned foundation and monitoring in place, with mechanisms for handling changes in demand or requirements. The system should be designed to detect failure and automatically heal itself.

Best Practices


Before architecting any system, foundational requirements that influence reliability should be in place. For example, you must have sufficient network bandwidth to your data center. These requirements are sometimes neglected (because they are beyond a single project's scope). This neglect can have a significant impact on the ability to deliver a reliable system. In an on-premises environment, these requirements can cause long lead times due to dependencies and therefore must be incorporated during initial planning.

With AWS, most of these foundational requirements are already incorporated or may be addressed as needed. The cloud is designed to be essentially limitless, so it is the responsibility of AWS to satisfy the requirement for sufficient networking and compute capacity, while you are free to change resource size and allocation, such as the size of storage devices, on demand.

The following questions focus on these considerations for reliability.

REL 1: How do you manage service limits?
REL 2: How do you manage your network topology?

AWS sets service limits (an upper limit on the number of each resource your team can request) to protect you from accidentally over-provisioning resources. You will need to have governance and processes in place to monitor and change these limits to meet your business needs. As you adopt the cloud, you may need to plan integration with existing on-premises resources (a hybrid approach). A hybrid model enables the gradual transition to an all-in cloud approach over time. Therefore, it's important to have a design for how your AWS and on-premises resources will interact as a network topology.

Change Management

Being aware of how change affects a system allows you to plan proactively, and monitoring allows you to quickly identify trends that could lead to capacity issues or SLA breaches. In traditional environments, change-control processes are often manual and must be carefully coordinated with auditing to effectively control who makes changes and when they are made.

Using AWS, you can monitor the behavior of a system and automate the response to KPIs, for example, by adding additional servers as a system gains more users. You can control who has permission to make system changes and audit the history of these changes.

The following questions focus on these considerations for reliability.

REL 3: How does your system adapt to changes in demand?
REL 4: How do you monitor your resources?
REL 5: How do you implement change?

When you architect a system to automatically add and remove resources in response to changes in demand, this not only increases reliability but also ensures that business success doesn't become a burden. With monitoring in place, your team will be automatically alerted when KPIs deviate from expected norms. Automatic logging of changes to your environment allows you to audit and quickly identify actions that might have impacted reliability. Controls on change management ensure that you can enforce the rules that deliver the reliability you need.

Failure Management

In any system of reasonable complexity it is expected that failures will occur. It is generally of interest to know how to become aware of these failures, respond to them, and prevent them from happening again.

With AWS, you can take advantage of automation to react to monitoring data. For example, when a particular metric crosses a threshold, you can trigger an automated action to remedy the problem. Also, rather than trying to diagnose and fix a failed resource that is part of your production environment, you can replace it with a new one and carry out the analysis on the failed resource out of band. Since the cloud enables you to stand up temporary versions of a whole system at low cost, you can use automated testing to verify full recovery processes.

The following questions focus on these considerations for reliability.

REL 6: How do you back up data?
REL 7: How does your system withstand component failures?
REL 8: How do you test resilience?
REL 9: How do you plan for disaster recovery?

Regularly back up your data and test your backup files to ensure you can recover from both logical and physical errors. A key to managing failure is the frequent and automated testing of systems to cause failure, and then observe how they recover. Do this on a regular schedule and ensure that such testing is also triggered after significant system changes. Actively track KPIs, such as the recovery time objective (RTO) and recovery point objective (RPO), to assess a system's resiliency (especially under failure-testing scenarios). Tracking KPIs will help you identify and mitigate single points of failure. The objective is to thoroughly test your system-recovery processes so that you are confident that you can recover all your data and continue to serve your customers, even in the face of sustained problems. Your recovery processes should be as well exercised as your normal production processes.

Key AWS Services

The AWS service that is essential to Reliability is Amazon CloudWatch, which monitors runtime metrics. The following services and features support the three areas in reliability:


Refer to the following resources to learn more about our best practices for Reliability.

Reliability Pillar
How do I manage my AWS service limits?
Embracing Failure: Fault-Injection and Service Reliability
AWS Limit Monitor
Service Limits
Service Limits Reports Blog
Amazon Virtual Private Cloud
AWS Shield
Amazon CloudWatch
Amazon S3
Backup Archive and Restore Approach Using AWS
Managing your AWS Infrastructure at Scale
AWS Disaster Recovery
AWS Amazon VPC Connectivity Options
AWS Premium Support
Trusted Advisor