HubSpot Site Reliability Engineer Interview: Rounds, Questions and Preparation

What the job involves

Site Reliability Engineers (SREs) at global tech companies like HubSpot ensure that large-scale, distributed systems are reliable, scalable, and efficient. They combine software engineering and systems engineering to build automation, monitor services, and respond to incidents, often working closely with development and infrastructure teams. Day to day, an SRE might write code to automate deployments, analyze metrics to prevent outages, and participate in on-call rotations to troubleshoot production issues.

Role and Technical Knowledge

1. 1

   What is the difference between a Site Reliability Engineer and a DevOps Engineer?

   Highlight that SRE is a specific implementation of DevOps principles with a focus on reliability, using software engineering to solve operations problems, while DevOps is a broader cultural and process movement.

2. 2

   Explain SLI, SLO, and SLA. How would you use them in practice?

   Define each term clearly: SLI is a metric, SLO is a target for that metric, SLA is a contract with consequences. Give an example like request latency and how you'd set an SLO and monitor it.

3. 3

   What is an error budget and why is it important?

   Explain that it is the allowed amount of unreliability (1 - SLO) over a period, used to balance feature velocity and reliability. Mention how it informs release decisions.

4. 4

   How does Linux memory management work? What tools would you use to diagnose a memory leak?

   Cover virtual memory, paging, and OOM killer. Mention tools like top, free, vmstat, and valgrind for leaks, and how to interpret their output.

Practical Scenarios

1. 5

   A service is suddenly returning 500 errors for all users. How do you troubleshoot?

   Walk through a structured approach: check dashboards and logs, identify recent changes, verify dependencies, and roll back if needed. Emphasize communication and blameless postmortem.

2. 6

   You need to design a highly available and scalable web application on AWS. What components would you use?

   Mention load balancers, auto-scaling groups, multi-AZ deployments, managed databases with replication, and caching. Discuss trade-offs between cost and reliability.

3. 7

   How would you automate the deployment of a microservice to Kubernetes?

   Describe a CI/CD pipeline: build, test, containerize, push to registry, and deploy via kubectl or Helm. Include health checks and rollback strategies.

4. 8

   You notice a sudden spike in latency for your API. What metrics would you check and how would you mitigate?

   Check request rates, error rates, latency percentiles, and resource utilization. Mitigate by scaling, optimizing queries, or enabling caching, and then investigate root cause.

Behavioural and HR

1. 9

   Tell me about a time you had to troubleshoot a technical problem under pressure. How did you handle it?

   Use the STAR method: describe the situation, task, action, and result. Highlight calmness, systematic debugging, and communication with stakeholders.

2. 10

   Describe a situation where you made a mistake that impacted a project. What did you learn?

   Show accountability, explain how you fixed it, and emphasize the lesson learned and how you prevented recurrence. Avoid blaming others.

3. 11

   How do you prioritize tasks when you have multiple urgent issues?

   Discuss assessing impact and urgency, using frameworks like Eisenhower matrix, and communicating with your team to align priorities.

4. 12

   Why do you want to work as an SRE, and why at a company like HubSpot?

   Connect your interest in reliability and automation to the company's scale and culture. Mention specific aspects like their engineering blog or focus on customer experience.

Coding and Automation

1. 13

   Write a Python script to monitor disk usage and send an alert if it exceeds a threshold.

   Use os.statvfs or shutil.disk_usage, compare to threshold, and send email or log. Discuss error handling and scheduling with cron.

2. 14

   How would you find the top 10 most frequent IP addresses in a large log file?

   Use shell commands like awk, sort, uniq, and head, or write a script. Explain scalability and memory considerations.

3. 15

   Given a list of server response times, write a function to calculate the 95th percentile.

   Sort the list, find the index at 95% (using nearest-rank or interpolation), and return the value. Discuss why percentiles matter in SRE.

4. 16

   How would you implement a simple health check endpoint for a web service?

   Describe an HTTP endpoint that checks dependencies (database, cache) and returns 200 if healthy, 503 otherwise. Mention timeouts and caching of results.