10 Infrastructure SRE Interview Questions and Answers for site reliability engineers

flat art illustration of a site reliability engineer

1. What is your experience with automation tools like Ansible, Puppet or Chef?

During my previous role as an Infrastructure SRE at XYZ company, I had extensive experience in using automation tools like Ansible, Puppet and Chef to manage and deploy our infrastructure. One specific project I spearheaded was automating our server deployment process using Ansible, which previously took us days to complete manually.

  1. First, I created a playbook that defined the necessary configurations for each server, such as setting up the firewall rules, installing essential packages, and configuring the network settings.
  2. Next, I created a list of variables that defined the specific settings for each server, such as the hostname, IP address, and operating system version. This allowed us to easily scale our infrastructure by simply updating the variables for each new server.
  3. Finally, I used Ansible's built-in inventory management to define which servers should be targeted for the playbook, and ran the playbook using a single command.

This automation reduced our server deployment time from several days to just a few hours, saving us valuable time and resources. Additionally, by using Ansible's idempotent nature, we were able to ensure our servers were configured consistently across our infrastructure, reducing the risk of errors or misconfigurations.

In conclusion, my experience with automation tools like Ansible, Puppet, and Chef has allowed me to streamline processes and improve efficiency within infrastructure management. I believe these tools are essential for any modern Infrastructure SRE and am confident in my ability to utilize them effectively.

2. What are some common methods you use for detecting and mitigating DDoS attacks?

One common method I use for detecting and mitigating DDoS attacks is implementing a traffic profiling system. By analyzing incoming traffic and identifying anomalies in traffic patterns, we can identify the source and type of DDoS attack. In addition, this system provides us with granular details on the type of traffic that is under attack.

Another effective method is leveraging a content distribution network (CDN) to offload traffic from the primary server. This not only minimizes the chances of an attack taking down our server, but it also provides us with a distributed network of servers that can absorb and filter out malicious traffic.

We can also use dedicated hardware or software solutions such as firewalls or intrusion prevention systems to filter out malicious traffic at the network level. By setting up rules within these systems that block traffic from known bad IPs, we can avoid congestion on our network and reduce the impact of a DDoS attack.

In one instance, while working as an infrastructure SRE for a gaming company, we experienced a sudden influx of traffic on our server that seemed to be originating from botnets. Our traffic profiling system caught the anomaly within seconds and alerted us to the attack. We quickly implemented our CDN and hardware solutions, which effectively mitigated the attack and minimized downtime for our gaming platform.

3. How do you measure uptime from a service and infrastructure perspective?

As an infrastructure SRE, measuring uptime is crucial to ensure that the service is always available and reliable for users. To effectively measure uptime from a service and infrastructure perspective, I use the following metrics:

  1. Total uptime: This is the total time the service has been available in a given period. For instance, if the service is expected to be available 24/7, then the total uptime for a week will be 168 hours. If the service was available for 162 hours, then the total uptime for that week will be 96.43%.
  2. Downtime incidents: This metric helps to determine the frequency and duration of downtime incidents. By tracking the number of downtime incidents, I can identify recurring issues and prioritize remediation efforts. For example, if the service experiences downtime incidents every Thursday night, I could investigate whether there is a weekly batch job that is causing the issue.
  3. Mean time to recover (MTTR): This metric measures how long it takes to recover from downtime incidents. The lower the MTTR, the quicker the service can be restored, minimizing the impact on users. For instance, if an incident caused five minutes of downtime, and the service was restored twenty minutes later, then the MTTR would be 20 minutes.
  4. Mean time between failures (MTBF): This metric helps to predict the likelihood of future downtime incidents. By calculating how long it takes for a failure to occur, I can identify trends and proactively address potential issues. For example, if the service experiences failures every six months on average, I could implement preventative measures such as increasing redundancy to prevent future downtime.
  5. Service level agreements (SLAs): SLAs are agreements between a service provider and users that define the level of service that will be provided. By tracking whether SLAs are being met, I can ensure that the service is meeting user expectations. For example, if the SLA states that the service will be available 99.9% of the time, I can track whether this target is being met.

By using these metrics, I can effectively measure uptime from a service and infrastructure perspective. For example, by tracking these metrics, I was able to improve the uptime of a mission-critical service from 98% to 99.9% in six months.

4. What methods do you use for ensuring redundancy in critical services?

Ensuring redundancy in critical services is of utmost importance for the stability and availability of services. To achieve this, I use the following methods:

  1. Load Balancers: I configure load balancers for essential services like databases and web servers, which helps distribute traffic across multiple servers. This method helps to prevent a single point of failure, and in case one of the servers fails, the load balancer redirects traffic to the remaining servers.
  2. Replication: Replication of databases to different geographical regions ensures that data is available even if a whole region fails. The replication process occurs in near real-time, ensuring that the latest data is available when needed. This method lowers the chance of data loss and ensures service availability to our clients.
  3. Active-Active Data Centers: Deploying a primary data center with all essential services up and running, and have a secondary data center in another location with the same services installed but inactive. I ensure that the secondary data center is up and running and prepared to take over the services in a disaster event. By having an active-active data center set up model, it reduces the downtime to near zero, ensures data consistency, and provides a seamless failover experience to our clients.
  4. Continuous Monitoring: Monitoring the services repeatedly with automated tools to detect any unusual behavior in system performance. With constant monitoring, potential issues can be identified and resolved before they cause service disruption. Having a monitoring solution in place helps me to achieve high availability in service delivery, which is critical for stable infrastructure.

By using these methods, I have successfully ensured redundancy in critical services in my current role, and my team has achieved over 99% uptime. We have also been able to reduce incident escalations by 40% and improve disaster recovery by 60%. I believe these methods are crucial for achieving high availability in a production environment.

5. Have you ever faced a problem where there was no easy solution, how did you approach it?

Yes, I faced a major issue last year where our system went down without any warning during peak hours. It was a mission-critical system that provided real-time data to our clients, and downtime even for a few minutes could have resulted in huge financial losses. After extensive analysis, we found that the issue was caused by a third-party service provider whose system was integrated with ours. They had made some updates without informing us, and it caused integration failure and system downtime.

  1. The first step I took was to quickly assemble a cross-functional team of developers, data analysts, and system admins to work on the issue together.
  2. We immediately contacted the third-party service provider and explained the urgency of the situation. We explained that their update caused downtime to our system, and we needed their help in resolving the issue as soon as possible.
  3. While waiting for the provider to revert, we collected and analyzed the logs to identify the root cause of the problem. It was a challenging task because the log data was scattered across multiple systems and formats.
  4. Once we identified the cause, we developed a temporary workaround to restore the system's functionality immediately.
  5. Then we created a permanent solution that involved updating our system to work with the new API changes that the third-party provider had made.
  6. After thorough testing of both the temporary and permanent solutions, we deployed the permanent fix into production.
  7. We monitored the system closely for the next few days to make sure there were no more issues and that the system was running smoothly.

As a result of our team's quick and decisive action, we were able to minimize downtime to just under an hour. This was much less than the amount of downtime that would have occurred if we had not acted fast. Additionally, our clients were very appreciative of our transparency in communicating the issue and the steps we took to resolve it.

6. What measures do you take to ensure the security of the infrastructure/end users?

As an Infrastructure SRE, I prioritize the security of the infrastructure and end users by implementing several measures:

  1. Regular security audits: I conduct regular security audits to identify vulnerabilities and risks within our infrastructure. These audits help me stay ahead of potential cyber attacks and data breaches.
  2. Implementing multi-factor authentication: To ensure that only authorized personnel have access to the infrastructure, I implement multi-factor authentication across all systems and applications. This extra layer of security provides an added safeguard against unauthorized access.
  3. Encrypting sensitive data: All sensitive data is encrypted at rest and in transit to ensure that even if there is a breach, the data remains protected.
  4. Continuous monitoring: I use various monitoring tools to continuously monitor the infrastructure for any suspicious activities or unauthorized access attempts. This helps me detect and respond to potential security threats in real time.
  5. Regular backups: To ensure that important data is not lost in the event of a security breach or system failure, I regularly backup all critical data and store it in a secure location.

Thanks to these measures, in my previous role as an Infrastructure SRE, I was able to prevent a potential cyber attack on our infrastructure, and also achieved a 99.9% uptime rate with zero security breaches for a period of six months.

7. What skills are essential for successfully monitoring and debugging systems at scale?

Successfully monitoring and debugging systems at scale requires a combination of technical and soft skills.

  1. Technical Skills: A deep understanding of the infrastructure stack, including operating systems, networking, databases, and storage systems, is essential for infrastructure SREs. Familiarity with monitoring tools such as Grafana, Prometheus, Nagios, and Zabbix is also necessary. In addition, proficiency in at least one programming language like Python, Ruby, Go or Java can be beneficial.
  2. Soft Skills: Infrastructure SREs will need excellent communication skills to work effectively as part of a team. To confidently communicate complex systems to non-technical stakeholders, it is necessary to be articulate and able to understand the recipient level of knowledge effectively. Additionally, the ability to think logically, systematically and laterally is key to resolve issues quickly and effectively.
  3. Metric-Driven Monitoring: An infrastructure SRE must know how to set the appropriate performance metrics and thresholds for the system. Metric-driven monitoring can quickly highlight infrastructural changes or issues that need to be resolved. A successful SRE should be able to create dashboards that track the system's stability in real-time.
  4. Automation: Automation is essential for maintaining constant monitoring and fast debugging of systems. Infrastructure SREs must be able to fully automate the configuration of monitoring tools, the troubleshooting process' response, and even the mitigation of issues by applying changes to the system automatically.

By using these skills in conjunction with one another, I was able to create a comprehensive monitoring and debugging system for a company whose application running in a cloud environment was facing constant crashes.

  • Technical ability: I implemented monitoring tools (Prometheus, Grafana, Nagios) and collected data on the infrastructure, system behavior, and applications.
  • Data analysis: I used the data to clearly identify critical performance metrics and set the monitoring thresholds. Additionally, I adjusted parameters to increase performance scaling up to meet customer demand.
  • Automation: I automated the troubleshooting process to reduce the overhead of manual intervention, making the company functional 24/7. I also automated fixes of known issues to allow the software to work around the bugs.
  • Communication: I worked closely with development and business teams of the company to understand their needs, and sometimes guided them through issues to improve the overall user experience.

8. What performance benchmarks do you use to track the performance of critical services?

As an Infrastructure SRE, monitoring and tracking the performance of critical services is a key responsibility. To accomplish this task, I rely on the following performance benchmarks:

  1. Throughput: This is the number of requests served per second by the critical service. I use this to ensure that the service is handling requests efficiently and not becoming overwhelmed during peak periods. A benchmark of at least 100 requests per second is one of the targets I aim for.
  2. Latency: This is the time it takes for a request to be processed and returned by the service. I pay close attention to this metric, as it directly impacts user experience. In general, I aim for a latency of under 200 milliseconds.
  3. Error Rate: This metric represents the number of requests that return an error status code (e.g. 404 or 500). I track this closely to ensure that error rates remain low - ideally less than 1%.
  4. Resource Utilization: This metric tracks the usage of resources like CPU, RAM and disk storage. By monitoring resource utilization, I can identify potential bottlenecks before they become a problem. A benchmark of at least 80% resource utilization is what I aim for, as anything higher than that could result in performance degradation.

To illustrate the effectiveness of these performance benchmarks, I recently used them to optimize the performance of a critical microservice that was experiencing latency issues. After implementing changes to the service's architecture and configuration, its latency dropped from an average of 500 milliseconds to around 50 milliseconds. Additionally, throughput increased by 60% while resource utilization remained at a manageable level of 70%. Most importantly, user experience improved significantly, resulting in a decrease in support tickets related to the service's functionality.

9. What is your experience with cloud infrastructure? (AWS, Azure, Google Cloud, etc.)

During my previous role at a large e-commerce company, I was responsible for migrating their entire infrastructure to AWS. This involved designing and implementing an architecture that would support the company's growing user base, as well as managing the migration process while ensuring minimal downtime.

  1. First, I conducted a thorough analysis of the company's existing infrastructure and identified potential areas for improvement. This included things like optimizing the usage of resources, implementing automated scaling, and improving security.
  2. I then created a detailed roadmap for the migration, which involved breaking down the process into smaller, manageable steps. This helped ensure that each task was completed on time and in the correct order.
  3. Next, I started setting up the new infrastructure on AWS, using a combination of EC2 instances, RDS, and S3 buckets. I also implemented DevOps tools such as Jenkins and Ansible to streamline the deployment process.
  4. To ensure minimal downtime during the migration, I set up a multi-region failover and a load balancer. This meant that traffic could be redirected seamlessly between the old and new infrastructure as required.
  5. Finally, I conducted extensive testing to ensure that the new infrastructure was functioning correctly and that there were no issues with scalability or security. I also implemented monitoring tools to continuously track the performance of the infrastructure.

Overall, the migration to AWS was a success and resulted in a significant reduction in infrastructure costs, as well as improved performance and scalability. The new architecture was able to handle traffic spikes without issue, and the company's uptime increased significantly as a result of the migration.

10. How do you evaluate and test new technologies before integrating them into the infrastructure?

Before integrating new technologies into our infrastructure, it is crucial to evaluate and test them to ensure that they meet our needs and are compatible with our existing systems. To do this, I follow a thorough evaluation process that includes the following steps:

  1. Identify the problem or need - I start by identifying why we need a new technology and what problem it aims to solve. This helps me narrow down our options and avoid investing time and resources in solutions that are not efficient or effective in solving our problem.
  2. Research potential solutions - Once I've identified the problem, I research potential solutions, looking at factors such as compatibility, ease of use, scalability, cost, and user reviews. I also prioritize solutions that have been tested and proven by other companies in similar industries.
  3. Prototyping and testing - After narrowing down the options, I create a prototype of the proposed solution and test it in a controlled environment to identify any potential issues or bugs. I also involve end-users in the testing process to gather feedback and ensure that the solution meets their needs.
  4. Data analysis - Once the testing is complete, I analyze the data gathered from the prototype testing and end-user feedback. I look at metrics such as speed, performance, security, and ease of use. Using this data, I determine whether the solution is viable for integration into our infrastructure.
  5. Implementation and monitoring - If the solution passes our evaluation process, it moves to the implementation phase, where we integrate it into our existing infrastructure. I monitor its performance and user feedback for several weeks to ensure that it is functioning as intended and meeting our expectations.

Using this evaluation process has helped me choose the most appropriate technologies to integrate into our infrastructure. In my previous job, we were able to improve our website's speed by 40% by integrating a new caching technology that went through this evaluation process. The technology improved our website's loading time, increasing user satisfaction, and engagement, leading to a 15% increase in revenue.


Congratulations on making it through these 10 Infrastructure SRE interview questions and answers! Now that you've aced the interview, it's time to prepare for the next steps in your job search process. One of the next steps is to craft a standout cover letter that showcases your skills and experience. Check out our guide on writing a cover letter for Site Reliability Engineers to help you create a compelling introduction to your potential employers. Another important step is to create an impressive CV that highlights your achievements and qualifications in the field of site reliability engineering. Our guide on writing a resume for Site Reliability Engineers provides an in-depth guide to help you create a standout CV that will catch the attention of hiring managers. Finally, if you're looking for new remote opportunities in the site reliability engineering field, don't forget to check out our remote job board. Our job board is updated regularly with exciting new opportunities that match your skills and experience, so be sure to check back frequently for the latest listings. Best of luck in your job search, and we hope to see you onboard a remote rocketship soon!

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