10 Fault tolerance and resiliency Interview Questions and Answers for site reliability engineers

flat art illustration of a site reliability engineer

1. Can you explain your experience with designing and implementing fault-tolerant systems?

Throughout my career as a Software Engineer, I've had significant experience designing and implementing fault-tolerant systems. In my previous role at XYZ Inc, I was part of a team that designed and implemented a highly available application that had a 99.99% uptime rate.

  1. To achieve this level of availability, we began by designing our application using a microservice architecture that allowed us to isolate and scale individual components as needed.
  2. We also implemented real-time monitoring and alerts using tools like Prometheus and Grafana. This allowed us to detect issues early and respond quickly to prevent downtime.
  3. In addition, we built in redundancy and failover mechanisms to ensure that if one component failed, the system as a whole would still function. As a result, even if a server went down, our application would automatically route traffic to healthy servers, ensuring continuous availability.
  4. We also conducted extensive testing of our fault tolerance mechanisms using chaos engineering tools like Gremlin. Through these tests, we were able to identify and fix potential failure points before they became actual issues.

All of these measures resulted in a highly resilient and fault-tolerant system that provided reliable service to our customers. As a result, we were able to increase customer satisfaction and reduce downtime-related costs.

2. How do you identify potential points of failure in a distributed system?

Identifying potential points of failure in a distributed system is critical to ensuring that the system remains stable and available. My process for identifying these points of failure involves:

  1. Conducting a thorough review of the system architecture to gain a clear understanding of how the different components interact with each other.

  2. Utilizing load testing tools to put the system under stress and observe how it performs. By analyzing the results of these tests, I can identify any areas that might be prone to failure under certain conditions.

  3. Monitoring the system's performance in real-time to detect any anomalies or issues that may arise. This can involve utilizing monitoring tools that allow me to track metrics such as CPU usage, memory usage, and network traffic.

  4. Working with the development team to ensure that any potential bottlenecks or points of failure are addressed during the development process. By collaborating with the team, I can help to identify potential issues before they become critical problems.

By following these steps, I was able to help identify a potential point of failure in a distributed system I worked on in my previous role. During load testing, we noticed that the system struggled to handle high levels of traffic during peak periods, which led to significant performance degradation. By analyzing the data and working with the development team, we were able to identify a bottleneck in the system architecture and implement changes to increase its capacity, resulting in improved performance during peak periods.

3. What techniques have you used to monitor system health and performance?

At my previous company, I implemented a variety of monitoring techniques to ensure system health and performance. One of the most effective techniques was implementing a centralized logging system using the ELK stack (Elasticsearch, Logstash, and Kibana).

  1. First, we set up Elasticsearch to store our logs in a highly available and fault tolerant manner.
  2. Next, we used Logstash to parse our logs and send them to Elasticsearch.
  3. Finally, we used Kibana to create visualizations and dashboards to help us monitor system health and performance.

Using this system, we were able to quickly identify bottlenecks and other issues that were impacting performance. For example, we noticed that certain API calls were taking longer than expected and were able to identify the root cause - a third-party API was experiencing intermittent connectivity issues. By identifying and addressing these issues early on, we were able to ensure that our system remained performant and highly available.

4. How do you prioritize and approach resolving incidents that may impact system reliability?

As an experienced Fault Tolerance and Resiliency professional, working with distributed systems, I have developed a reliable approach to prioritize and resolve incidents that may impact the reliability of a system. First, I make sure to fully understand the issue at hand, its exact symptoms, and the extent of its impact, which helps me determine the severity level of the incident at hand.

  1. Once I have determined the severity level of the incident, I adhere to the Service Level Agreements (SLAs) set out to commit to the users, and then proceed to rank them in order of their priority level.
  2. In doing so, I leverage the Severity and Priority matrix that I have developed in my past work experience, which takes into account not only the impact of the issue but also its likelihood of occurrence, the length of time it has been present, and the number of users impacted, among other factors.
  3. In conjunction with the matrix, I ensure to involve all stakeholders in identifying and resolving the issue, including other technicians in the team, relevant vendors or service providers, and most importantly the users.
  4. I then proceed to resolve the incident using the SLAs as a guide and document the entire process from start to finish for future reference.

By following this approach in my previous role, I was able to minimize downtime by 90%, increased reliability by 95%, created a culture of continuous improvement, and improved the overall customer satisfaction rating.

5. Can you share an example of a particularly challenging incident you helped resolve and what you learned from it?

During my time as a Site Reliability Engineer at XYZ Company, we experienced a major service outage that affected 50% of our customers. We immediately initiated our incident response plan and formed an incident response team including myself and other team members from different departments.

  1. The first step was to identify the root cause. I conducted a thorough investigation and discovered that the outage was caused by a misconfigured load balancer that was not able to handle the sudden surge in traffic.
  2. Next, we worked on mitigating the issue. I proposed a solution to manually distribute the traffic to the remaining servers while we fixed the misconfigured load balancer.
  3. After about an hour, we were able to successfully fix the load balancer and distribute the traffic back to the servers. We then conducted a post-incident review to assess our response and identify areas for improvement.

As a result of this incident, we implemented several improvements to our infrastructure including regular load testing and improved monitoring of the load balancers. We also revised our incident response plan to ensure faster response times and better communication between teams.

Our efforts paid off as we were able to reduce the mean time to resolve incidents from 2 hours to just under 30 minutes. Additionally, we improved our service uptime from 95% to 99.9% over the next six months.

6. How do you ensure that system changes are thoroughly tested before deployment to production?

At my previous company, we implemented a rigorous testing methodology to ensure that all system changes were thoroughly tested before deployment. Here are the steps we followed:

  1. Unit testing: Developers were required to write unit tests for every piece of code they wrote. These tests were automated and run on every code change to identify any regressions.
  2. Integration testing: Before any system change was released to test, it had to go through a thorough integration testing process. This process involved testing the changes in a staging environment that was identical to our production environment.
  3. User acceptance testing: Once the changes passed integration testing, they were released to our user acceptance testing (UAT) environment. Our UAT environment was a replica of our production environment, so we could test the changes in a realistic environment. Our UAT team consisted of a representative sample of our users, who would test the changes and provide feedback.
  4. Regression testing: After any changes were made and tested, we ran regression testing to ensure that no other parts of the system were affected negatively. Regression testing was automated, which saved us a significant amount of time and reduced the chance for human error.

By implementing this methodology, we were able to significantly reduce the number of bugs and issues that made it to production. In 2022, our production system had a 99% uptime, which was a significant increase from the previous year.

7. What experience do you have with container orchestration platforms such as Kubernetes?

I have extensive experience with container orchestration platforms such as Kubernetes. In my previous role as a DevOps engineer at XYZ Company, I was responsible for migrating our applications to a Kubernetes-based infrastructure.

  1. Firstly, I conducted a thorough analysis of our existing infrastructure and determined the optimal configuration for our Kubernetes deployment. This included configuring node labels and affinities, as well as analyzing resource utilization to ensure our container pods were appropriately sized.
  2. Next, I created a CI/CD pipeline that automatically deployed our applications to Kubernetes clusters. I utilized Jenkins and Ansible to build and package our application code, and used Kubernetes manifests to ensure our application was properly deployed across multiple environments.
  3. Finally, I implemented monitoring and logging tools to gain visibility into our Kubernetes clusters. I utilized Prometheus and Grafana to monitor resource utilization and container health, and implemented Elasticsearch and Kibana for centralized logging of container logs.

As a result of these efforts, we were able to increase our deployment frequency by over 50%, reduce application downtime by 70%, and improve overall system resiliency. Additionally, our team was able to more efficiently manage and scale our infrastructure, leading to significant cost savings for the organization.

8. How do you collaborate with development teams to ensure reliability and scalability of applications?

Collaborating with development teams is key to ensure the reliability and scalability of applications. One way I ensure this is by conducting regular code reviews with the team to identify potential issues that could negatively impact the application's performance. During these code reviews, I work with the team to optimize the code and identify any areas that might cause scalability issues.

Another approach I take is to establish clear communication channels within the team. For instance, I organize regular standup meetings where team members provide progress updates and discuss any issues that may be hindering their work. This allows me to identify any potential bottlenecks and provide solutions for them, thus ensuring that the team can continue to work efficiently.

  1. One project where this approach proved successful was a mobile app for a fintech company. During the development process, we identified that the application was consuming too much time and resources when loading images.
  2. Following a code review, we managed to optimize the code and reduce image loading time by 50%. This not only improved the app's performance but also ensured that the app was scalable to handle increased user demand.
  3. In another project, we identified that database performance was impacting the responsiveness of the application. By conducting regular standups and collaborating with the developers, we identified the importance of implementing a caching mechanism to reduce the number of requests made to the database.
  4. Following the implementation of the caching mechanism, we observed a 60% improvement in the application's responsiveness. This resulted in a better user experience and increased customer satisfaction.

Overall, my collaborative approach ensures that application reliability and scalability are optimized throughout the development process, leading to successful outcomes for both the team and end-users.

9. What measures do you take to ensure system security and compliance?

Ensuring system security and compliance is crucial to maintaining a stable and reliable system. As a fault tolerance and resiliency expert, I implement various measures to ensure that the system is safe and meets regulatory compliance standards. Some of the measures I employ include:

  1. Firewalls: I use firewalls to monitor and block unauthorized access to the system. This helps prevent cyber attacks and ensures data security.
  2. Vulnerability assessments: I perform regular vulnerability assessments to identify and address any security loopholes that may exist in the system. This helps ensure that the system is fully secure and compliant.
  3. Data encryption: I use encryption techniques to protect sensitive data and ensure its confidentiality. Encryption algorithms such as AES-256 are used to protect data while being transmitted over the network.
  4. Multi-Factor Authentication: I employ multi-factor authentication (MFA) to protect user accounts and prevent unauthorized access. With MFA, a user is required to authenticate using a combination of two or more methods such as a password and SMS code.
  5. Security incident response: I develop comprehensive security incident response plans that outline the steps to be taken in case of a security breach. This helps minimize the damage caused by an attack and ensures business continuity.

As a result of my efforts, the system has experienced zero security breaches and has been fully compliant with all regulatory requirements. Furthermore, customer satisfaction with the security of the system has increased by 30% since my implementation of these measures.

10. Can you explain your experience with disaster recovery and high availability architecture?

In my previous role as a Solutions Architect at XYZ Corp, I was responsible for designing and implementing disaster recovery and high availability solutions for our mission-critical applications. One particular project involved migrating our customer-facing e-commerce platform to the cloud and ensuring it was fault-tolerant and resilient to various failures.

  1. First, I conducted a thorough analysis of the application's architecture and identified potential single points of failure.
  2. Next, I designed a multi-node architecture that utilized load balancers and replicated databases to ensure high availability.
  3. Then, I implemented a backup and recovery strategy that automated the process of creating backups and restoring data in the event of a failure.
  4. To test the solution's effectiveness, we conducted multiple simulations of various failure scenarios, including network outages and server failures. In each case, the system was able to recover within seconds without any loss of data.
  5. As a result of our efforts, our e-commerce platform achieved an uptime of 99.999%, and our customers experienced no downtime or disruptions during the migration.

Overall, my experience with disaster recovery and high availability architecture has taught me the importance of thorough analysis, careful planning, and rigorous testing to ensure that mission-critical systems can withstand any unforeseen events with little to no impact on the end-users.


Preparing for a site reliability engineer interview can be nerve-wracking, but by practicing these fault tolerance and resiliency interview questions and familiarizing yourself with their answers, you can feel more confident during the interview. After the interview, the next step is to showcase your skills in a well-crafted cover letter. Check out our guide on writing a standout cover letter to give yourself an advantage in the application process. Another important step is to prepare an outstanding CV that highlights your experience and skills as an SRE. To help you create an impressive resume, we’ve put together a guide on writing a CV for a site reliability engineer. You can find it here. Finally, if you're in search of a new remote site reliability engineer job, use our website to search for the latest opportunities. Visit our job board for remote site reliability engineer jobs to kickstart your career in 2023.

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