Add Case 6: Circuit Breaker pattern for CNPG failover#6
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shahabhameed merged 1 commit intoinfobloxopen:mainfrom Apr 9, 2026
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Implements a circuit breaker that detects database failures and fails fast instead of blocking on 30s connection timeouts. Three-state machine (Closed→Open→HalfOpen) with configurable threshold and probe timeout. Broken baseline: 88/100 (p95=2145ms, 14.7% errors, 320 reqs) Fixed baseline: 100/100 (p95=10ms, 60% errors, 599 reqs) New files: - pkg/cases/breaker.go — Circuit breaker state machine - pkg/cases/circuitbreaker_case.go — Handler with LAB: STEP6 TODOs - docs/circuitbreaker_case.md — Deep-dive documentation Modified: - pkg/api/handler.go — Register /cases/circuitbreaker route - pkg/driver/scenarios.go — Add circuitbreaker scenario (60s, fault at t=15s) - All docs updated (FACILITATOR, LAB, AGENT_PROMPTS, LEADERBOARD, README)
shahabhameed
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Summary
Adds a new workshop case teaching the circuit breaker resilience pattern. When the CNPG primary is killed, the application without a breaker blocks every request on 30-second TCP timeouts, collapsing throughput. The fix enables a breaker that detects the outage after 5 failures and rejects subsequent requests in <1ms, preserving throughput and latency.
Key design decisions
Reuses CNPG infrastructure from Case 5 — same cluster, same fault injection function. Lab instructions include reverting Case 5 fixes (back to 1 instance) so the outage window is visible.
Higher errors = better service — The breaker intentionally raises error rate (60% vs 15%) but drops p95 by 200x and doubles throughput. The [MaxErrRate: 0.75] threshold accommodates this.
Breaker disabled by default — [Threshold: 0] ships as the broken state. Students search for LAB: STEP6 TODO and set [Threshold: 5, Timeout: 5s].
Broken state (Threshold=0)
Score: 68/100
Error rate: ~15%
p95: ~3,145ms
Each kill = full outage until pod restarts + Blocks on TCP timeout
Fixed state (Threshold=5, Timeout=5s)
Score: 100/100
Error rate: ~60%
p95: ~10ms
Fails fast, throughput maintained