AWS Architecture Blog

Chaos Engineering in the cloud

For many years, Chaos Engineering was viewed as a mechanism to help surface the “known-unknowns” (things that we are aware of, but do not fully understand) in our environments or “unknown-unknowns” (things we are neither aware of, nor fully understand).

Using Chaos Engineering, chaos experiments have been conducted on infrastructure, applications, and business processes that identified weaknesses and prevented outages for many organizations; yet, while Chaos Engineering found a home across various industries, like Financial Services, Media and Entertainment, Healthcare, Telecommunication, Hospitality and others, it has been slow in its adoption.

A different perspective on Chaos Engineering

For the last decade, Chaos Engineering had the reputation of being a mechanism to “purposely break things in production”, which stopped many companies from adopting it. The ultimate goal of Chaos Engineering is not about breaking production systems.

Chaos Engineering offers a mechanism that allows your teams to gain deep insights into your workloads by executing controlled chaos experiments that are based on a real-world hypothesis. These experiments have a clear scope that defines the expected impact to the workload and includes a rollback mechanism where there is availability or recovery processes in place to mitigate the failure.

Chaos Engineering drives operational readiness and best practices around how your workloads should be observed, designed, and implemented to survive component failure with minimal to no impact to the end user. Therefore, Chaos Engineering can lead to improved resilience and observability, ultimately improving the end-user’s experience and increasing organizations’ uptime.

The Shared Responsibility Model for resilience

When you build a workload in the Amazon Web Services (AWS) Cloud, we (at AWS) are responsible for the “resilience of the cloud”; this means, we are responsible for the resilience of the services and infrastructure offered on the AWS Cloud. This infrastructure is composed of the hardware, software, networking, and facilities that run AWS Cloud services.

Your responsibility as a customer is the “resilience in the cloud”, meaning your responsibility is determined by the AWS Cloud services that you consume. This determines the amount of configuration work, recovery mechanisms, operational tooling, and observability logic that are needed to make the workload resilient (Figure 1).

AWS Shared Responsibility Model for resilience

Figure 1. AWS Shared Responsibility Model for resilience

Resilience in the cloud

Separation of duties creates interesting challenges in resilience:

  • How can you build workloads that will mitigate enough failure modes to meet your resilience objective, if you are not responsible for operating the underlying services that you rely on?
  • How are your workloads performing if one or more AWS services are impaired, a network disruption occurs, or a natural disaster strikes?

While there is distinct guidance on these questions in the AWS Well-Architected Framework’s Reliability Pillar, one question still remains: can your team/organization simulate a controlled event in pre-production or production that would give them confidence that the observability tooling, incident response, and recovery mechanisms will protect the workload from a disruption with minimal to no customer impact?

If you have been operating in a regulated environment, like the Financial Services industry, Healthcare, or the Federal Government, you can cite that the quarterly/yearly disaster-recovery (DR) exercises and your business continuity plan help with such simulations.

Planned DR exercises have a clear structure and scope: employees know that they have to be ready on a certain date and time, and they will execute the runbooks and playbooks that are hopefully up-to-date on that day. In essence, this validates a failover of a known-state. While DR exercises can provide a high level of confidence that operations will continue in a secondary region without being dependent on any services in the primary site, these exercises do not provide the ability to detect and mitigate the different types of failure modes that may be encountered in a real-world scenario.

Disaster recovery and failure in the real world

For example, in 2012, Hurricane Sandy took down critical infrastructure services when it struck the Northeast US, resulting in power and telecommunication outages on the East Coast. Many companies’ business continuity plans did not account for staff living in zones impacted by natural disaster. Clearly, these individuals would/will not be able to assist during a real-life DR event.

Executing a DR plan quarterly or yearly may not be enough to prepare an organization for real-world events: they can come without notice and in many different flavors, like faulty deployments or configurations, hardware failures, data and state corruption, the inability to connect to a third-party provider, or natural disasters. Most may not require the execution of your DR plan but, instead, challenge observability, high-availability strategy, and incident-response processes.

Chaos Engineering real-world events

How can you prepare for unknown events? Chaos Engineering provides value to your organization by allowing it to get ahead of unexpected disruptions by continuously injecting controlled, real-world disruptions as a scheduled job, in your software development lifecycle, and/or continuous integration and continuous delivery (CI/CD) pipelines at the cloud-provider, infrastructure, workload-component, and process level.

Consider Chaos Engineering a resilience guardian: it gives the confidence, control, and rigor needed to ensure the experiment does not impact the customer, or quickly stop the experiment if it does. Using these mechanisms, your teams can learn from faults in a controlled environment and observe, measure, and improve the workloads’ resilience, plus validate the logs, metrics, and that alarms are in place to notify operators within a predetermined timeframe.

Finding and amending deficiencies

When incorporating Chaos Engineering into your day-to-day operations, workload deficiencies will surface and need to be addressed. Chaos Engineering experiments run in production that surface unexpected behavior will only minimally impact customers, if at all, compared with real-world, unexpected disruptions. Controlled experiments are executed with a clear scope of impact. Experts are present to observe the experiment and automated rollback mechanisms executed. In the worst-case scenario, these experts will get hands-on and remediate the disruption on the spot.

If an experiment surfaces unknown behavior, there is a Correction of Error (COE) analysis. The COE is a process for improving quality by documenting and addressing issues, focusing on identifying and amending root causes.

Using the COE, we can explore the customer interaction with the workload and understand the customer impact. This can provide further insights on what happened during the event and give way to deep dives into the component that caused failure. If the fault is not identifiable, more observability should be added to the workload.

Additionally, incident-response mechanisms are reviewed to validate that a disruption was detected, key stakeholders are notified, and escalations processes begin in the predetermined timeframe. Prioritizing new findings and, based on impact, adding them to the issue back log, and addressing known risks are the keys to successful Chaos Engineering and mitigating future impact to the workload.

Chaos Engineering on AWS

To get started with Chaos Engineering on AWS, AWS Fault Injection Simulator (AWS FIS) was launched in early 2021. AWS FIS is a fully managed service used to run fault injection experiments that simulate real-world AWS faults. This service can be used as part of your CI/CD pipeline or otherwise outside the pipeline via cron jobs.

As demonstrated in Figure 2, AWS FIS can inject faults sequentially or simultaneously, introducing faults across different types of resources, Amazon Elastic Compute Cloud, Amazon Elastic Container Service, Amazon Elastic Kubernetes Service, and Amazon Relational Database Service. Some of these faults include:

  • Termination of resources
  • Forcing failovers
  • Stressing CPU or memory
  • Throttling
  • Latency
  • Packet loss

Since it is integrated with Amazon CloudWatch alarms, you can setup stop conditions as guardrails to rollback an experiment if it causes unexpected impact.

AWS Fault Injection Simulator integrates with AWS resources

Figure 2. AWS Fault Injection Simulator integrates with AWS resources

As Chaos Engineering should provide as much flexibility as possible when it comes to fault injection, AWS FIS integrates with external tools, such as Chaos Toolkit and Chaos Mesh, to expand the scope of failures that can be injected to your workload.


Chaos Engineering is not about breaking systems but rather creating resilient workloads that can survive real-world events with minimal-to-no customer impact, by finding the “known-unknowns” and/or “unknown-unknowns” that can cause such events. Additionally, these mechanisms help improve operational excellence and resilience through developer and observability best practices, allowing you to catch deficiencies before they escalate into large-scale events and therefore improve the customers experience.

If you’d like to know more, please join us at AWS re:Invent 2022, where we will present multiple sessions on Chaos Engineering. Also, explore Chaos Engineering Stories!

Laurent Domb

Laurent Domb

Laurent is a Chief Technologist for US Federal Financial Services at Amazon Web Services (AWS) and the WW Lead for Chaos Engineering of the Resilience TFC. Over the past 20 years, he worked in different roles from leading teams in product management, consulting, and IT to working as a Principal Solutions Architect, Consultant, and Developer. These roles provided him with a deep understanding of the various facets of the IT industry across many verticals, insights and skills needed to lead teams and develop talent, mapping business challenges to technology and a drive to deliver results.