Failure Mode Analysis

Failure Mode Analysis

Purpose

Systematically identify failure scenarios for proposed features and design mitigations that maintain system resilience.

Inputs

• Feature or infrastructure change being analyzed
• System architecture (services, databases, APIs, third-party dependencies)
• Current reliability requirements (SLA/SLO targets)
• Existing monitoring and alerting setup

Process

Step 1: List System Components

Enumerate all components involved: services, databases, APIs, third-party dependencies, caches, queues, CDNs, DNS, and any shared infrastructure.

Step 2: Enumerate Failure Modes Per Component

For each component, systematically consider:

• Network failures: Timeout, DNS resolution failure, TLS handshake failure, connection reset, packet loss
• Data failures: Corruption, inconsistency between stores, migration errors, schema drift, encoding issues
• Resource exhaustion: Memory leak, CPU saturation, connection pool exhaustion, disk full, file descriptor limits
• Dependency failures: Third-party API down, rate limited, schema change, authentication revoked, region outage
• State failures: Race conditions, stale cache serving wrong data, split-brain in distributed systems, phantom reads

Step 3: Assess Cascade Potential

Map the failure tree: if component X fails, what else breaks? Identify single points of failure and shared dependencies. Determine blast radius for each failure mode.

Step 4: Design Mitigations

For each failure mode, define:

• Graceful degradation: What functionality survives? What's the user experience during failure?
• Retry strategy: Exponential backoff with jitter, circuit breaker thresholds, max retry limits
• Fallback behavior: Cached data, default values, error states, read-only mode
• Recovery procedure: Automatic vs manual recovery, estimated time to recovery, data reconciliation steps

Step 5: Define Monitoring Signals

For each failure mode, specify the metric, log pattern, or alert that detects it. Include detection latency — how quickly will you know?

Step 6: Plan Rollback Strategy

Define rollback approach: feature flags for instant disable, database rollback scripts, deployment rollback procedure, data cleanup if needed.

Output Format

Failure Mode Table

Cascade Diagram

[Component A fails]
  ├── [Component B] — degraded (uses cached data)
  ├── [Component C] — down (hard dependency)
  │   └── [Component D] — down (depends on C)
  └── [Component E] — unaffected (independent)

Rollback Checklist

• Feature flag to disable: [flag name]
• Database rollback: [migration name / script]
• Deployment rollback: [procedure]
• Data cleanup: [steps if needed]
• Communication: [who to notify]

Quality Checks

• Every external dependency has failure analysis
• Cascade paths are fully mapped with blast radius
• Mitigations don't introduce new failure modes
• Monitoring covers detection of each identified failure
• Rollback strategy is defined and tested
• Recovery time estimates are documented

Evolution Notes