Health checks in HLD - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a health check in system design?

A health check is a simple test that a system or service runs to confirm it is working correctly and ready to handle requests.

beginner

Why are health checks important in distributed systems?

They help detect failures early, allowing systems to reroute traffic or restart services to keep the system reliable and available.

intermediate

What is the difference between a liveness probe and a readiness probe?

A liveness probe checks if the service is alive and should be restarted if it fails. A readiness probe checks if the service is ready to accept traffic.

beginner

Name two common methods used for health checks.

1. HTTP endpoint check: The system responds with a status code indicating health. 2. TCP socket check: The system accepts connections on a port to show it is alive.

intermediate

How do health checks improve system scalability?

By quickly identifying unhealthy instances, health checks allow load balancers to avoid sending traffic to them, ensuring only healthy instances handle requests, which keeps the system scalable and responsive.

What does a readiness probe indicate?

A If the service is alive and should be restarted

B If the service is ready to accept traffic

C If the system has enough memory

D If the database is connected

A readiness probe checks if the service is ready to accept traffic.

Which method is commonly used for health checks?

A HTTP endpoint check

B FTP file transfer

C Email notification

D DNS lookup

HTTP endpoint check is a common method where the service responds with a status code indicating health.

What happens if a liveness probe fails?

A The service is restarted

B Traffic is routed to the service

C The service is marked ready

D Nothing happens

If a liveness probe fails, the system restarts the service to recover it.

Why are health checks critical for load balancers?

A To monitor user activity

B To encrypt traffic

C To increase database speed

D To identify unhealthy instances and avoid sending them traffic

Load balancers use health checks to avoid sending traffic to unhealthy instances.

Which of these is NOT a purpose of health checks?

A Detecting service failures

B Restarting unhealthy services

C Increasing CPU speed

D Improving system reliability

Health checks do not affect CPU speed.

Explain the role of health checks in maintaining system availability.

Think about how systems stay up and running smoothly.

Describe the difference between liveness and readiness probes with examples.

Consider when a service should be restarted versus when it should receive traffic.