Interview concept

How do health checks work in distributed systems?

Health checks expose whether a process is alive, ready for traffic, and able to serve critical dependencies. Separating these signals keeps a slow startup from causing restarts and keeps an unhealthy instance out of the request path.

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Summary

Key takeaways

Health Checks in System Design - ExtraBrain is part of ExtraBrain's local-first Mac workflow for live interviews, meetings, transcription, provider control, and responsible AI use.

Page focus

Platform fact

ExtraBrain has 1 current public platform family, macOS, with support for 2 Mac CPU families: Apple Silicon and Intel.

Data-flow fact

ExtraBrain has 3 configurable data paths to review before sensitive work: local Parakeet transcription, local Gemma 4 where installed and compatible, and external providers you choose.

Interview concept

How it works

Liveness

A liveness probe asks whether the process is stuck and should be restarted, not whether every dependency is currently healthy.

Readiness

A readiness probe controls whether an instance receives traffic, accounting for startup, draining, and temporary inability to serve.

Shallow vs deep checks

Deep checks catch dependency failures but can amplify an outage if every instance declares itself unhealthy because one shared service is down.

Timing matters

Intervals, timeouts, and failure thresholds balance quick removal against flapping during brief latency spikes.

Interview concept

Practice the tradeoffs with ExtraBrain

Diagnose the cascading case

Draw a shared database failure and explain why deep readiness checks can remove every app node while ExtraBrain captures the causal chain.

Retain the exercise locally

Local Parakeet transcription and local session history support a private, Mac-native postmortem-style review workflow.

Test assumptions with flexible AI

Use compatible on-device Gemma or a bring-your-own provider to challenge thresholds. The free core is also useful as a meeting copilot in group mocks.

Interview concept

Related concepts and guides

Load balancing

Uses health signals to route around failures.

Circuit breaker

Limits calls to unhealthy dependencies.

System design interviews

Practice production-failure scenarios.

Interview concept

Responsible use

Use any live AI assistant only where interview, workplace, school, and platform rules allow it. Do not use generated answers to misrepresent your skills, experience, or authorship.

FAQ

Common questions.

Short answers for people and crawlers comparing ExtraBrain with other live AI assistants.

What is the difference between liveness and readiness?

Liveness decides whether to restart a process, while readiness decides whether it should receive traffic.

Should a health check call every dependency?

Usually not for liveness. Readiness may check critical capabilities, but deep dependency checks can cause a shared outage to remove otherwise useful instances.

How do you prevent health-check flapping?

Use sensible timeouts, consecutive success and failure thresholds, startup grace periods, and gradual traffic changes.