Top 40 site reliability engineering (SRE) interview questions to assess candidates

For modern tech companies, site reliability engineers (SREs) play an integral role in ensuring the reliability, scalability, and performance of complex systems and applications.

The role requires a unique blend of software engineering skills and operations expertise, enabling SREs to build and maintain robust and scalable IT infrastructure and ensure maximum uptime and reliability of your digital services. 

Failing to accurately assess a candidate’s skills during the hiring process can lead to service disruptions and reliability issues. But how can you make sure you’re able to evaluate their skills and experience impartially and objectively?

For this, you need a rigorous evaluation process, featuring: 

• Pre-employment skills tests to assess all applicants’ knowledge

• The right SRE interview questions to identify the perfect candidate

In this article, we’ll discuss the benefits of using a skill-based approach to hiring your next site reliability engineer and give you our selection of the best SRE interview questions to ask candidates, along with our guidelines on how to evaluate their answers. 

Top 20 SRE interview questions and answers

Below, you’ll find our selection of the top 20 interview questions for site reliability engineers. We’ve also provided sample answers and guidelines to help you assess candidates' expertise and their potential fit for the role, even if you don’t have the same level of technical knowledge as them. 

1. Describe a script you've developed to solve a problem. What language did you use and why?

Although this question focuses on the solution rather than on the problem, the first thing candidates should do is to give you context, i.e. explain the problem they faced.

The best applicants will then explain how they considered additional requirements, as well as the need for scalability and maintainability of their script. Then, they’ll provide details about the language they chose and why. For example: 

• Python for its simplicity and rich libraries, or 

• JavaScript for its asynchronous capabilities, or

• Go for its efficiency and performance

2. How do you ensure your code is clean, maintainable, and efficient?

Skilled candidates will be deeply familiar with the importance of clean code. Look for specific best practices they mention. For example, they might explain that they: 

• Write modular code

• Use clear and meaningful variable names

• Implement consistent coding styles

• Conduct thorough testing with unit tests and integration tests

They might also talk about the importance of code reviews, giving and receiving feedback, and maintaining clear documentation to ensure the codebase is transparent for others. 

Mentioning specific tools like linters or formatters, and principles such as DRY (Don't Repeat Yourself) or SOLID, indicates a strong understanding of coding best practices.

You can also use our Clean Code test to assess an engineer’s ability to write easy-to-maintain code.

3. What is your experience with using version control systems such as Git?

Expect candidates to describe their proficiency with Git or similar systems through specific examples, such as:

• Branching and merging

• Handling merge conflicts

• Collaborating with team members

Knowledge of advanced features like rebase, cherry-pick, and tagging is a plus. Their answers should also demonstrate an understanding of best practices for integrating version control into CI/CD pipelines.

4. What is multithreading?

Multithreading is the ability of a CPU to execute multiple threads concurrently, each thread running a part of a program. 

A good answer would outline the benefits of multithreading, such as improved application performance and responsiveness, and its challenges, like the complexity of thread synchronization and potential for deadlocks. 

Expect skilled applicants to give you examples of using multithreading in past projects and be familiar with synchronization mechanisms, such as mutexes or semaphores.

5. Explain the difference between a process and a thread in a Linux system.

The difference between the two is that: 

• A process is an instance of a running program with its own dedicated memory space

• A thread is the smallest unit of processing that can be scheduled by an operating system

Threads operate within a process and share its memory space. 

6. Describe how you would use cgroups in Linux for resource management.

Skilled candidates will explain that cgroups (control groups) allow for the allocation, prioritization, and monitoring of system resources like CPU time, system memory, network bandwidth, or combinations of these resources among user-defined groups of tasks. 

They may describe past situations where they've used cgroups, for example to:

• Limit resource hogging by certain processes

• Ensure critical services have enough resources

• Manage containerized applications efficiently

Use our Linux test to evaluate candidates’ proficiency in this operating system.

7. How do you monitor system performance? What tools do you use?

A comprehensive approach to system performance monitoring features a variety of tools, such as: 

• System-level monitors like top, htop, vmstat

• Application performance monitoring (APM) tools

• Logging tools

Some more advanced solutions are: 

• Prometheus for metric collection and alerting

• Grafana for dashboards

• ELK Stack (Elasticsearch, Logstash, Kibana) for log aggregation and visualization

Skilled candidates might also explain that monitoring should not just be reactive, i.e. fixing issues as they arise, but also proactive, identifying potential issues before they impact users.

8. Explain the differences between NFS and SAN storage solutions.

Look for answers explaining that: 

• NFS (Network File System) is a protocol allowing remote access to files over a network, presenting storage at the file level

• SAN (Storage Area Network) is a specialized, high-speed network that gives access to consolidated, block-level storage

NFS is often used for sharing files across a network of devices, making it suitable for situations where ease of access and file sharing are a priority, while SAN is typically used in environments requiring high performance, such as databases, where direct access to the disk block is necessary. 

9. Explain the difference between UDP and TCP. How does each affect web application performance and reliability?

Expect answers to cover that: 

• TCP (Transmission Control Protocol) is a connection-oriented protocol that ensures reliable and ordered delivery of a stream of bytes. It's beneficial for applications where data integrity is critical. 

• UDP (User Datagram Protocol) is a connectionless protocol that offers faster transmissions but without guarantees on delivery or order. It’s suitable for applications where speed is more critical than reliability, like streaming or gaming. 

Candidates might discuss trade-offs, noting how TCP's error correction mechanisms can introduce latency but ensure reliability, whereas UDP's lightweight nature can enhance performance but at the risk of data loss or out-of-order arrival.

10. How do you manage package dependencies and updates in a production environment?

Skilled candidates will talk about strategies such as using virtual environments, containerization, or specific tools (like npm for Node.js or pip for Python) to manage packages. 

They should emphasize the importance of testing updates in a development or staging environment before applying them to production to avoid unexpected downtime. 

11. How do you decide when a task should be automated? What factors do you consider?

The decision whether to automate a task should be based on factors such as:

• The task’s frequency and complexity

• The potential for errors

• The time investment required for automation

Experienced candidates would also consider the impact on the team and whether automating the task would reduce toil or improve efficiency. They might also discuss evaluating the return on investment (ROI) of automation and ensuring that automated processes are documented and maintainable.

12. What’s your experience with configuration management tools?

Expect seasoned SREs to have hands-on experience with tools like Ansible, Chef, Puppet, or SaltStack and to give examples of instances where they've used them to automate the setup and management of software and servers. 

Look for examples of how these tools have helped ensure consistency across environments, facilitated scalability, and improved operational efficiency. 

13. Explain the concept of infrastructure as code (IaC). How can it be applied in managing cloud resources?

IaC is the practice of managing and provisioning infrastructure through code, rather than through manual processes. It enables consistent and repeatable deployment of servers and services with the help of tools such as Terraform, CloudFormation, or Azure Resource Manager templates. 

Application examples might include:

• Automating the creation of cloud environments

• Scaling resources based on demand

• Ensuring compliance with security policies

You can use TestGorilla’s Terraform test to evaluate candidates’ proficiency with it, or add some of our Terraform interview questions to go a step further.

14. What specific strategies do you use to make your automation scripts maintainable and scalable?

Look for answers that mention the importance of readability, modularity, and reusability of code when discussing automation scripts and how to maintain them. 

For this, site reliability engineers might: 

• Use version control for scripts

• Document the code and its purpose

• Apply consistent naming conventions

• Break down scripts into smaller, manageable functions or modules

To ensure scalability, they would need to create scripts that can handle variable loads and environments dynamically. 

Candidates might also explain how they've used parameters, environment variables, or configuration files to adapt scripts to different scenarios and needs. Insights into testing strategies, such as unit tests or integration tests for automation scripts, are a plus. 

15. How do you approach cost optimization for cloud resources?

To optimize the costs of cloud resources, SREs would need to: 

• Analyze current and projected costs with tools provided by cloud platforms

• Use autoscaling to adjust resources based on demand

• Select the right types and sizes of resources (e.g., compute instances) for the task at hand

• Use spot instances or reserved instances where appropriate

• Set up budget alerts to monitor and control expenses

Skilled applicants will also mention that different deployment architectures, such as serverless deployments or containers, also impact costs.

16. Explain the differences between IaaS, PaaS, and SaaS. When would you use each?

Look for answers that outline the following differences and use cases: 

• IaaS (Infrastructure as a Service) provides virtualized computing resources online. It’s best used for custom, scalable computing environments. AWS EC2 is an example.

• PaaS (Platform as a Service) offers a platform where customers can develop, run, and manage applications without building and maintaining the infrastructure. Examples include Heroku and Google App Engine.

• SaaS (Software as a Service) is a software distribution model in which service providers host applications and make them available to customers over the internet. Examples include Salesforce, Docusign, Zelt, and even TestGorilla.

17. Tell us about your experience with containerization and orchestration in the cloud. Have you used Kubernetes or similar tools?

Skilled applicants will be proficient in containerization technologies like Docker and orchestration tools like Kubernetes, Docker Swarm, or Amazon ECS. Look for examples where candidates have successfully used these tools to improve deployment speed, reliability, and scalability. 

Candidates might also talk about container registries, continuous integration and continuous deployment (CI/CD), and managing containerized workloads at scale.

Use TestGorilla’s Docker and Kubernetes tests to evaluate SREs’ ability to work independently with each tool.  

18. Describe the difference between logging, monitoring, and tracing. How does each contribute to observability?

Expect candidates to explain that: 

• Logging is the recording of discrete events that happen in the system

• Monitoring is the continuous collection and analysis of metrics to assess system health

• Tracing is tracking the execution path of requests to diagnose problems or performance bottlenecks

The three practices enhance observability by collecting data on system performance and behavior, helping identify issues and inform the team’s decisions.

19. Define the concepts of SLI, SLO, and SLA. How do they interrelate in the context of SRE?

Candidates should explain that:

• Service Level Indicators (SLIs) are specific, measurable characteristics of the service, such as latency or error rate

• Service Level Objectives (SLOs) are the target values for SLIs that the service aims to meet

• Service Level Agreements (SLAs) are contractual agreements with customers that include consequences for not meeting SLOs

Skilled SREs will understand how these concepts help to set, measure, and manage the performance and reliability of services. 

20. How do you set up thresholds for alerts?

The best candidates will know how to set up alert thresholds that balance information and noise. Expect them to talk about analyzing the normal operating ranges of systems and services and looking into historical performance data.

Candidates should also mention the practice of simultaneously using static thresholds for fixed values, and dynamic thresholds, which adjust based on trends or patterns. 

For example, they might set static thresholds for critical system resources, such as 90% disk space usage, to prevent service disruption. As for dynamic thresholds, they could use them for metrics like CPU usage, where normal ranges might vary depending on the time of day or workload.

20 additional site reliability engineering interview questions you can ask candidates

Below, you’ll find 20 extra interview questions you can use when looking to hire a SRE for your business, split up in four categories. 

General interview questions for SREs

1. Explain the concept of error handling and how you implement it in your code.

2. Explain the importance of code reviews. What do you look for when reviewing someone else's code?

3. Describe a situation where you had to refactor legacy code. What approach did you take and what were the outcomes?

4. Describe the steps you take to secure a server.

5. Discuss a time when you had to perform a system migration. What were the key considerations?

SRE interview questions related to automation

1. Tell us about the automation project you are most proud of. What tools did you use?

2. Explain how you've implemented automated alerts for system failures or performance issues.

3. How do you manage and monitor the execution of your automated tasks?

4. Describe a situation where an automated process you developed saved significant time or resources.

5. How do you test your automation scripts before deploying them in production?

Cloud-related SRE interview questions

1. Discuss an instance where you had to design a highly available cloud architecture. What components did you use?

2. How do you secure cloud environments and manage access control?

3. Explain how you would migrate an on-premise application to the cloud.

4. How do you handle disaster recovery in a cloud environment?

5. What strategies do you use to ensure data privacy and compliance in the cloud?

SRE interview questions related to monitoring and observability

1. Explain your process for implementing a distributed tracing system.

2. How do you determine which metrics are important for an application's performance?

3. How do you ensure that alerts are actionable and not overwhelming?

4. Describe how you have used dashboards for real-time system monitoring.

5. Explain how you would monitor a microservices architecture differently from a monolithic architecture.

How to evaluate SRE skills

Site reliability engineers design and implement automation solutions, monitor system performance, conduct post-incident reviews and optimize system reliability and scalability.

To perform all those tasks, they need to be proficient in multiple programming languages and tools such as Python, Java, AWS, Google Cloud, Docker, Kubernetes, and more. Additionally, they also need to have strong analytical and problem-solving skills along with the ability to lead cross-functional teams.

You must assess the skills of every candidate before you move on to the interview stage. However, resume screening is not the ideal way to gauge a candidate's knowledge and abilities.

A combination of skills tests and the right interview questions provide objective insights into candidates’ abilities. With TestGorilla, you can create your own custom assessments by combining up to five different skill tests. 

Some of the tests you might use when looking for a site reliability engineer are: 

• Cloud System Administration: Evaluate applicants’ experience with Windows and Linux administration and their proficiency in cloud solutions and networking.

• Cloud computing platforms such as AWS, Google Cloud Platform, and Microsoft Azure: Use our tests to assess your candidates’ expertise in the cloud computing platform(s) your organization uses.

• PostgreSQL: Find applicants with hands-on experience in managing relational database systems with PostgreSQL.

• PHP (Coding): Intermediate-Level Algorithms: This test uses a short coding assignment to evaluate your candidates’ coding skills in PHP.

• Critical Thinking: Are your applicants able to quickly evaluate information and make sound judgments using their analytical skills? Find out with this test. 

• Essential tools from the SRE toolkit, such as Git, Terraform, Kubernetes, Docker: 

• Software Engineering: Site reliability engineers need to be skilled software engineers, too. Make sure applicants have the right competencies with this test. 

Hire the best site reliability engineers for your company

Successful IT infrastructure management and automation require a diverse set of skills, which you need to evaluate during the recruitment process if you want to be sure to make the right hiring decision. 

Use skills assessments and structured interviews to identify the best candidates who have the right technical expertise, problem-solving abilities, and teamwork skills required for the role.

Find the best SRE for your company with the help of TestGorilla. Sign up for a free demo to talk to one of our experts and see whether our platform is the right fit for you – or try out our free plan to start evaluating your candidates today.