Fail Fast
When to Use This Skill
Fail fast is a design pattern that validates preconditions before executing expensive or irreversible operations. When validation fails, the system immediately reports the error rather than proceeding and failing later in an unpredictable state.
flowchart TD
subgraph validation[Validation Phase]
A[Request] --> B{Preconditions Met?}
end
subgraph execution[Execution Phase]
C[Execute Operation]
D[Success]
end
subgraph failure[Failure Phase]
E[Report Error]
F[No Side Effects]
end
B -->|Yes| C
C --> D
B -->|No| E
E --> F
%% Ghostty Hardcore Theme
style A fill:#65d9ef,color:#1b1d1e
style B fill:#fd971e,color:#1b1d1e
style C fill:#a7e22e,color:#1b1d1e
style D fill:#a7e22e,color:#1b1d1e
style E fill:#f92572,color:#1b1d1e
style F fill:#f92572,color:#1b1d1e
The key insight: fail before you start, not in the middle.
When to Apply
| Scenario | Apply Fail Fast? | Reasoning | | ---------- | ------------------ | ----------- | | Invalid user input | Yes | User error, report immediately | | Missing required config | Yes | Can't continue safely | | Insufficient permissions | Yes | Operation will fail anyway | | Resource allocation failure | Yes | Partial allocation is worse | | Network timeout | No | Use graceful degradation | | Cache miss | No | Expensive path still works |
Decision rule: Fail fast on precondition failures. Degrade gracefully on runtime failures.
Implementation
GitHub Actions Workflow Validation
See examples.md for detailed code examples.
Go Function with Precondition Validation
See examples.md for detailed code examples.
Techniques
Fail Fast Techniques
Comprehensive techniques for implementing fail fast patterns:
Early Termination
Stop execution immediately when errors occur:
- Shell strict mode (
set -euo pipefail) - GitHub Actions matrix fail-fast
- Go error propagation
- Circuit breakers
Strict Mode Execution
Enable strictest validation and error detection:
- Shell/TypeScript/Go strict modes
- Linter enforcement
- Schema validation
Assertion Patterns
Validate assumptions and fail if they're wrong:
- Runtime assertions
- Contract validation (pre/post conditions)
- Invariant checks
- Type guards
Error Escalation
Determine when to throw vs return, panic vs recover:
- Throw vs return error
- Error aggregation vs first-error-wins
- Panic vs recoverable errors
- Exit codes
Timeout Enforcement
Prevent operations from running indefinitely:
- Operation timeouts
- Job timeouts
- Circuit breaker timeouts
- Deadlock detection
See reference.md for additional techniques and detailed examples.
Comparison
These patterns are complementary, not contradictory:
See examples.md for detailed code examples.
| Error Type | Pattern | Example | | ------------ | --------- | --------- | | Missing config | Fail Fast | Can't start without database URL | | Database timeout | Graceful Degradation | Retry, then use cache | | Invalid input | Fail Fast | Reject malformed request | | API unavailable | Graceful Degradation | Use backup endpoint | | Insufficient permissions | Fail Fast | Don't attempt forbidden operation | | Rate limited | Graceful Degradation | Exponential backoff |
Anti-Patterns to Avoid
1. Late Validation
Validating after side effects have occurred.
See examples.md for detailed code examples.
2. Swallowing Errors
Continuing despite failures.
See examples.md for detailed code examples.
3. Partial Execution
Executing some operations before checking all preconditions.
See examples.md for detailed code examples.
4. Vague Error Messages
Failing fast but not explaining why.
# Bad: unhelpful error
[ -f "$CONFIG" ] || exit 1
# Good: actionable error message
[ -f "$CONFIG" ] || { echo "Config file not found: $CONFIG. Create it from config.example.yml"; exit 1; }
Examples
See examples.md for code examples.
Full Reference
See reference.md for complete documentation.