Wombat

WAF-REL-120 – Graceful degradation and fallback strategies MUST be documented and tested

Pillar: Reliability | Severity: 🟠 High | Category: Reliability Design | Automatable: Low

Description

Critical user journeys MUST continue in a degraded mode when non-essential dependencies fail. Fallback behavior, default responses, and feature degradation order MUST be documented. Degradation paths MUST be tested in staging and during chaos experiments. Non-critical features MUST be tiered so lower-priority functions can be disabled first.

Rationale

Risk Description

Risk

Hard dependencies on non-essential services turn partial failures into total outages.

Risk

Untested fallback paths often fail when first invoked during a real incident.

Requirements

  • Critical user journeys MUST continue in a degraded mode when non-essential dependencies fail.

  • Fallback behavior, default responses, and feature degradation order MUST be documented.

  • Degradation paths MUST be tested in staging and during chaos experiments.

  • Non-critical features MUST be tiered so lower-priority functions can be disabled first.

Implementation Guidance

  1. Document the requirement in a version-controlled policy, ADR, or standard.

  2. Assign ownership and establish a review cadence (e.g., quarterly).

  3. Implement the required configuration as code in Terraform or equivalent IaC.

Maturity Levels

Level Name Criteria

L1

Ad hoc – control not consistently applied

* Die Anforderung ist nicht einheitlich umgesetzt; Nachweis existiert nur punktuell oder fehlt.

L2

Standardised – policy defined and communicated

* Eine dokumentierte Policy oder ein Standard beschreibt die Anforderung.

L3

Integrated – automated validation in CI/CD

* Terraform-Checks oder IaC-Gates prüfen die Anforderung automatisch in CI/CD.

L4

Auditable – metrics and exceptions tracked

* Abdeckung, Ausnahmen und Qualitätsmetriken werden quartalsweise berichtet.

L5

Optimised – continuous improvement based on data

* Die Effektivität wird kontinuierlich gemessen und automatisch optimiert.

Checks

waf-rel-120.config.degradation-adr

Engine: config | Provider: any | Automated: No

Graceful degradation must be documented in ADR

Graceful degradation must be documented in ADR

Scope: file — docs/adr/degradation.md

Assertions: * exists attribute_exists — At least one ADR must document graceful degradation strategy.

Remediation: Graceful degradation must be documented in ADR

Compliant
# Example compliant with waf-rel-120.config.degradation-adr
Non-Compliant
# Example non-compliant with waf-rel-120.config.degradation-adr

waf-rel-120.config.chaos-test-evidence

Engine: config | Provider: any | Automated: No

Chaos test evidence for fallback paths must exist

Chaos test evidence for fallback paths must exist

Scope: file — docs/reliability/chaos-tests.md

Assertions: * exists attribute_exists — Chaos tests must demonstrate fallback behavior.

Remediation: Chaos test evidence for fallback paths must exist

Compliant
# Example compliant with waf-rel-120.config.chaos-test-evidence
Non-Compliant
# Example non-compliant with waf-rel-120.config.chaos-test-evidence

Evidence

  • Terraform configuration implementing the requirement.

  • Policy, ADR, or standard documenting the requirement.

  • Optional cloud console or API output confirming runtime state.

Related Controls

  • WAF-REL-050

  • WAF-REL-110

  • WAF-REL-130

  • WAF-OPS-020

  • WAF-OPS-040

  • WAF-AGN-040 == Regulatory Mapping

  • SRE Book (Google): Chapter 22 – Addressing Cascading Failures

  • AWS Well-Architected Framework: REL 9 – Mitigate deployment risks

  • Azure Well-Architected Framework: Reliability – Failure mode analysis

  • NIST CSF 2.0: RS.RP-01 – Response plan is executed