Infrastructure Engineer Interview Questions : Mock Interviews

From System Admin to Cloud Architect Journey

Alex began his career as a system administrator, spending most days manually configuring servers and responding to alerts. He often felt stuck in a reactive cycle, battling outages and performance bottlenecks on legacy systems. The turning point came during a major scaling failure, which made it clear that manual processes were no longer sustainable. Determined to evolve, Alex dedicated himself to learning cloud technologies on AWS and automation tools like Terraform and Ansible. He started treating infrastructure as code, building repeatable and reliable systems. This proactive, engineering-driven approach not only stabilized the platform but also accelerated development cycles. Over several years, his expertise grew, and he transitioned into a Principal Infrastructure Architect, now designing the resilient, large-scale systems he once struggled to maintain.

Infrastructure Engineer Job Skill Interpretation

Key Responsibilities Interpretation

An Infrastructure Engineer is the architect and custodian of a company's technological foundation, responsible for designing, building, and maintaining the entire IT infrastructure. This includes servers, networks, storage, and cloud services that underpin all software applications. Their core mission is to ensure the platform is reliable, scalable, and performs efficiently under any load. They are pivotal in building and managing automated systems using Infrastructure as Code (IaC) principles to eliminate manual errors and accelerate deployment speed. Furthermore, they are on the front lines of ensuring high availability and implementing robust disaster recovery plans, making their role critical to business continuity. In essence, they empower development teams to innovate and ship products confidently, knowing the underlying platform is solid and secure.

Must-Have Skills

• Cloud Platforms (AWS/GCP/Azure): You must be proficient in at least one major cloud provider to build and manage modern, scalable, and cost-effective infrastructure. This is the standard for today's technology companies.
• Infrastructure as Code (IaC): Mastery of tools like Terraform or Ansible is essential for automating the provisioning and management of infrastructure. This ensures consistency, reduces manual errors, and makes infrastructure versionable and repeatable.
• Containerization & Orchestration: You need deep expertise with Docker for containerizing applications and Kubernetes for orchestrating them at scale. This is fundamental for building microservices-based architectures.
• CI/CD Pipelines: The ability to design, build, and maintain CI/CD pipelines using tools like Jenkins, GitLab CI, or GitHub Actions is crucial. This automates the software delivery lifecycle, enabling faster and more reliable releases.
• Operating Systems: A strong command of Linux/Unix environments is non-negotiable. This knowledge is required for server administration, performance tuning, and troubleshooting..
• Networking Fundamentals: You must have a solid understanding of TCP/IP, DNS, HTTP, load balancing, and firewall configurations. This knowledge is critical for building secure and resilient systems.
• Monitoring and Observability: Proficiency with tools like Prometheus, Grafana, and the ELK Stack is required to monitor system health, diagnose issues, and ensure performance. Proactive monitoring prevents outages.
• Scripting Languages: Fluency in a scripting language like Python or Bash is essential for writing automation scripts, creating custom tools, and managing system tasks efficiently.
• Security Principles: You must be able to implement security best practices across the infrastructure, including IAM, network security, and vulnerability management. Security is a core responsibility, not an afterthought.

Preferred Qualifications

• Distributed Systems Design: Understanding concepts like consensus, replication, and fault tolerance allows you to design and build truly robust, large-scale systems that can withstand failures. This sets you apart as a senior-level candidate.
• Serverless Computing Experience: Familiarity with serverless technologies like AWS Lambda or Google Cloud Functions demonstrates that you are current with modern architectural patterns. It shows you can leverage managed services to optimize cost and reduce operational overhead.
• Advanced Database Management: Beyond basic setup, deep knowledge of database performance tuning, replication strategies, and sharding for both SQL and NoSQL databases is a powerful differentiator. It shows you can manage the data layer at scale.

The Shift From Ops to Engineering

The role of an Infrastructure Engineer represents a critical evolution from traditional System Administration. Where sysadmins often focused on manual server configuration, reactive troubleshooting, and ticket-based operations, the modern engineer adopts a software development mindset. This "engineering" approach means treating infrastructure as software—defining it in code, managing it with version control like Git, and deploying it through automated, testable pipelines. Instead of firefighting, the focus shifts to proactive design and building resilient, self-healing systems. This paradigm shift, often at the heart of DevOps culture, breaks down silos between development and operations. It enables infrastructure to be deployed and scaled as quickly and reliably as application code, which is essential for any company aiming for agility and rapid growth in a competitive market.

Mastering Cloud Native Technologies

To excel as an Infrastructure Engineer today, it is not enough to simply "lift and shift" on-premise workloads to the cloud. The goal is to master cloud-native technologies and principles. This means architecting systems that are born in the cloud and built to leverage its full potential, including containerization with Docker, orchestration with Kubernetes, and designing microservices that can be scaled independently. It involves embracing managed services (like RDS for databases or S3 for storage) to offload operational burdens and designing applications for failure by anticipating and mitigating potential outages. A cloud-native approach empowers organizations to achieve unprecedented levels of agility, scalability, and cost-efficiency. For an engineer, demonstrating proficiency in this area shows you can build for the future, not just maintain the present.

Security as a Core Infrastructure Pillar

In today's landscape, security is no longer a separate function handled by a different team; it is an integral part of the infrastructure engineering role. This concept, known as DevSecOps, involves "shifting left" to integrate security practices into every stage of the infrastructure lifecycle. For an Infrastructure Engineer, this means security is a primary consideration from the very beginning of the design process. Responsibilities include configuring secure network architectures (VPCs, subnets, security groups), implementing the principle of least privilege with Identity and Access Management (IAM), automating vulnerability scanning within CI/CD pipelines, and securely managing secrets. Hiring managers actively seek candidates who demonstrate a security-first mindset, as they are crucial for protecting company assets and building trust with users.

10 Typical Infrastructure Engineer Interview Questions

Question 1：Describe a time you had to troubleshoot a critical production outage. What was your process?

• Points of Assessment: Assesses your problem-solving methodology under pressure, your technical depth in diagnostics, and your communication skills during a crisis.
• Standard Answer: "In a previous role, our main e-commerce platform went down during a peak traffic period. My first step was to establish a communication channel with stakeholders to provide regular updates. Concurrently, I started the technical diagnosis by checking our monitoring dashboards in Grafana, which showed a spike in database CPU utilization. I checked the slow query logs and identified a poorly optimized query that was locking key tables. To immediately restore service, we rolled back the recent application deployment that introduced the query. For the long-term fix, I worked with the development team to rewrite and properly index the query, and we added more robust load testing to our CI/CD pipeline to prevent similar issues from reaching production."
• Common Pitfalls: Providing a vague answer without specific technical details. Blaming other teams without showing a collaborative problem-solving approach.
• Potential Follow-up Questions:
  • How did you ensure the rollback itself wouldn't cause further issues?
  • What monitoring tools were most crucial in diagnosing the problem?
  • What process changes were implemented to prevent this from happening again?

Question 2：How would you design a highly available and scalable infrastructure for a new web application on AWS?

• Points of Assessment: Evaluates your cloud architecture skills, understanding of core AWS services, and ability to design for resilience and growth.
• Standard Answer: "For a highly available application on AWS, I would start with a design that spans multiple Availability Zones (AZs). I'd place the web servers in an Auto Scaling Group behind an Application Load Balancer (ALB) to distribute traffic across the AZs and automatically scale based on demand. For the database layer, I would use Amazon RDS with a Multi-AZ deployment for automatic failover. Static content would be served from an S3 bucket with CloudFront as the CDN to reduce latency. This architecture ensures that the failure of a single component or even an entire AZ will not bring down the application."
• Common Pitfalls: Forgetting to mention Multi-AZ deployments. Neglecting key components like a CDN or proper load balancing.
• Potential Follow-up Questions:
  • How would you handle user session data in this stateless architecture?
  • What kind of monitoring and alerting would you set up for this environment?
  • How would you optimize this design for cost?

Question 3：Explain the concept of Infrastructure as Code (IaC) and why it is important. What tools have you used?

• Points of Assessment: Tests your understanding of core DevOps principles, your automation mindset, and your hands-on experience with relevant tools.
• Standard Answer: "Infrastructure as Code is the practice of managing and provisioning infrastructure through machine-readable definition files, rather than through physical hardware configuration or interactive configuration tools. It is important because it makes infrastructure provisioning repeatable, consistent, and auditable, treating it just like application code. It enables automation, reduces the risk of human error, and facilitates collaboration through version control. I have primarily used Terraform for declarative provisioning of cloud resources across AWS and GCP, and Ansible for configuration management tasks like installing software and applying security patches to servers."
• Common Pitfalls: Describing IaC as just "running scripts." Failing to explain the key benefits like versioning, repeatability, and idempotency.
• Potential Follow-up Questions:
  • What is the difference between a declarative tool like Terraform and a procedural tool like Ansible?
  • How do you manage state in Terraform, especially when working in a team?
  • Describe a complex module you have written in Terraform.

Question 4：Walk me through a CI/CD pipeline you have built or managed. What were the stages and what tools were involved?

• Points of Assessment: Assesses your practical experience with software delivery automation and your knowledge of the tools that enable it.
• Standard Answer: "I recently built a CI/CD pipeline for a microservice using GitLab CI. The pipeline would trigger on every merge request to the main branch. The first stage was 'build,' where we compiled the code and created a Docker image. The second stage was 'test,' which ran unit and integration tests against the new image. If tests passed, the 'scan' stage used a tool like Trivy to check for security vulnerabilities. Upon success, the image was pushed to our container registry. The 'deploy' stage then used Helm to roll out the new version to our Kubernetes staging environment. After manual approval, a final stage would promote the release to production with a canary deployment strategy."
• Common Pitfalls: Describing a very basic, linear pipeline without stages for testing or security. Being unable to explain the purpose of each stage.
• Potential Follow-up Questions:
  • How did you handle database schema migrations in this pipeline?
  • What strategies did you use to make the pipeline faster?
  • How did you manage secrets and credentials used by the pipeline?

Question 5：What is Kubernetes and what problem does it solve? Describe its main components.

• Points of Assessment: Evaluates your knowledge of container orchestration, which is a core technology in modern infrastructure.
• Standard Answer: "Kubernetes is an open-source container orchestration platform that automates the deployment, scaling, and management of containerized applications. It solves the problem of managing the complexity of running applications across a fleet of machines at scale. Its main components include the Control Plane, which makes global decisions about the cluster (like scheduling), consisting of the API Server, etcd, scheduler, and controller manager. Then there are the Worker Nodes, which are the machines that run the containers. Each node runs a Kubelet to communicate with the control plane and a container runtime like Docker to run the containers inside Pods."
• Common Pitfalls: Confusing Kubernetes with Docker. Being unable to name and describe the function of key components like the API server or etcd.
• Potential Follow-up Questions:
  • What is the difference between a Pod, a Deployment, and a StatefulSet?
  • How would you expose a service running in Kubernetes to the outside world?
  • How does Kubernetes handle self-healing?

Question 6：How do you handle secrets management in your infrastructure?

• Points of Assessment: Tests your awareness of security best practices, a critical aspect of the infrastructure role.
• Standard Answer: "My approach to secrets management is to never store secrets in plain text in version control. I advocate for using a dedicated secrets management tool like HashiCorp Vault or a cloud provider's service such as AWS Secrets Manager. In my a recent project, we used AWS Secrets Manager. Applications were granted IAM roles with permissions to retrieve specific secrets at runtime. For Kubernetes, we integrated it with Vault using the Vault agent sidecar injector, which automatically provides secrets to pods without the application needing to be aware of Vault. This ensures secrets are encrypted, access is audited, and rotation can be automated."
• Common Pitfalls: Suggesting storing secrets in environment variables in Git. Lacking a clear strategy and mentioning only ad-hoc solutions.
• Potential Follow-up Questions:
  • What is the difference between encryption in transit and encryption at rest?
  • How would you handle the initial "secret zero" problem of authenticating to the secrets manager itself?
  • What's your process for rotating secrets with zero downtime?

Question 7：You notice a service is experiencing high latency. What are the first few things you would check?

• Points of Assessment: Assesses your systematic troubleshooting and diagnostic skills, from high-level to low-level checks.
• Standard Answer: "First, I'd check our observability platform, starting with high-level dashboards to understand the blast radius—is it one service or the entire system? I'd look at application-level metrics like request rate, error rate, and latency (the RED method). Next, I would dive into the infrastructure metrics for the affected service: CPU, memory, and I/O on the hosts or pods. If those look normal, I would check dependencies like databases or downstream APIs for their own latency issues. Finally, I would inspect application logs for any errors or unusual patterns that correlate with the latency spike."
• Common Pitfalls: Jumping to a very specific, low-level cause without a structured approach. Forgetting to check dependencies.
• Potential Follow-up Questions:
  • What tools would you use for distributed tracing to pinpoint the bottleneck?
  • If you suspected a network issue, what commands would you use to diagnose it?
  • How do you differentiate between application latency and infrastructure latency?

Question 8：What is the difference between a load balancer and a reverse proxy?

• Points of Assessment: Tests your understanding of fundamental networking concepts and their practical applications.
• Standard Answer: "While they can be implemented using the same software, their conceptual roles are different. A load balancer is used to distribute incoming network traffic across multiple backend servers to improve reliability and capacity. Its main goal is to prevent any single server from becoming a bottleneck. A reverse proxy, on the other hand, sits in front of one or more web servers, intercepting requests from clients. It can provide functionalities like SSL termination, caching, compression, and request routing based on the URL, effectively acting as a gateway to the backend services. So, a load balancer is primarily for distribution, while a reverse proxy is for managing and protecting backend servers."
• Common Pitfalls: Saying they are the same thing. Being unable to provide distinct use cases for each.
• Potential Follow-up Questions:
  • Can you give an example of a popular reverse proxy software?
  • What are different load balancing algorithms you know?
  • Where would you place a Web Application Firewall (WAF) in relation to a reverse proxy?

Question 9：How would you automate the process of patching a fleet of 100 Linux servers with zero downtime?

• Points of Assessment: Probes your ability to design safe, automated operational procedures for a large-scale environment.
• Standard Answer: "To achieve this with zero downtime, I would use a rolling update strategy managed by a configuration management tool like Ansible. First, I would ensure our services are running in a highly available configuration behind a load balancer. My Ansible playbook would first remove a small batch of servers—say, 5%—from the load balancer's pool. Then, it would apply the patches, reboot the servers if necessary, and run a health check script to verify they are fully operational. Once the health checks pass, the playbook would add the patched servers back into the load balancer pool. This process would repeat for the next batch until all servers are updated, ensuring service availability throughout."
• Common Pitfalls: Suggesting a manual process or a "big bang" approach that would cause downtime. Forgetting crucial steps like health checks and draining connections from the load balancer.
• Potential Follow-up Questions:
  • How would you handle a patch that fails to apply on some servers?
  • What if a server fails its health check after patching?
  • How would you test this patching process before running it in production?

Question 10：Tell me about a project where you significantly improved performance or reduced infrastructure costs. What did you do and what was the result?

• Points of Assessment: Evaluates your ability to deliver business value through technical improvements and to quantify your impact.
• Standard Answer: "At my last company, our cloud bill was growing unsustainably, particularly our AWS EC2 costs. I initiated a cost optimization project. After analyzing our usage with AWS Cost Explorer and CloudWatch, I found that many instances were oversized for their workloads. I led an effort to resize instances based on their actual performance metrics. Additionally, I implemented an Auto Scaling policy for our development environments to shut them down outside of business hours. The combined result of rightsizing and scheduling was a 30% reduction in our monthly EC2 spend, saving the company over $15,000 per month without impacting performance."
• Common Pitfalls: Describing an improvement without specific metrics or results. Focusing only on the technical details without explaining the business impact.
• Potential Follow-up Questions:
  • What tools did you use to analyze the performance metrics of the instances?
  • How did you gain buy-in from development teams to implement these changes?
  • Did you consider using AWS Savings Plans or Reserved Instances as part of your strategy?

AI Mock Interview

It is recommended to use AI tools for mock interviews, as they can help you adapt to high-pressure environments in advance and provide immediate feedback on your responses. If I were an AI interviewer designed for this position, I would assess you in the following ways:

Assessment One：System Design and Architecture

As an AI interviewer, I will assess your ability to design robust, scalable, and cost-effective systems. For instance, I may ask you "Design the infrastructure for a real-time analytics platform that ingests millions of events per minute" to evaluate your fit for the role. This process typically includes 3 to 5 targeted questions on your design choices and trade-offs.

Assessment Two：Automation and IaC Proficiency

As an AI interviewer, I will assess your practical knowledge of automation principles and tools. For instance, I may ask you "Explain how you would use Terraform to manage a multi-cloud environment and what challenges you might face" to evaluate your fit for the role. This process typically includes 3 to 5 targeted questions about your coding practices, state management, and module design.

Assessment Three：Troubleshooting and Incident Response

As an AI interviewer, I will assess your problem-solving skills by presenting you with a hypothetical crisis. For instance, I may ask you "Users are reporting intermittent timeouts when accessing a critical service. The dashboards look normal. What are your next steps?" to evaluate your fit for the role. This process typically includes 3 to 5 targeted questions to test your logical thinking and diagnostic process.

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Authorship & Review

This article was written by David Miller, Principal Infrastructure Architect, and reviewed for accuracy by Leo, Senior Director of Human Resources Recruitment. Last updated: 2025-05

References

DevOps and SRE Concepts

• The SRE Book - Google
• What is DevOps? - AWS
• 12 Factor App

Cloud Platform Documentation

• AWS Well-Architected Framework
• Google Cloud Architecture Framework
• Microsoft Azure Well-Architected Framework

Infrastructure as Code Tools

• Terraform Documentation
• Ansible Documentation
• Kubernetes Documentation