Visual Notation
The CD Model uses specific visual elements to represent different concepts.
Understanding these symbols is essential for reading the model diagrams.
The following diagram provides a comprehensive reference for all visual elements used in EAC documentation, including stages, gates, environments, and test level indicators.
Start Elements
Start elements indicate entry points into the CD Model workflow.
These represent where work begins, typically when an engineer starts authoring changes on a local topic branch.
Automated Quality Gates
Automated quality gates are checkpoints that validate specific criteria before allowing progression to the next stage.
Examples:
- Tests passing
- Code quality standards (formatting, repository layout)
- Test coverage thresholds
- Security scan results
- Performance benchmarks
- Automated approvals based on quality metrics
If quality gates fail, the pipeline stops, preventing defects from progressing further.
Signoff Points
Signoff points represent formal approvals required at critical stages.
Types:
- Manual approvals from stakeholders or release managers
- Compliance artifact sign-offs
- Security review approvals
- Peer approval in the merge request
See Compliance for detailed signoff gate descriptions.
Exploration Activities
Exploration activities represent human-driven validation that complements automated testing.
Examples:
- Exploratory testing
- User acceptance testing (UAT)
- Stakeholder demos and feedback
- Manual verification of edge cases
Execution Hosts
Execution hosts are where automation is executed:
| Host | Description |
|---|---|
| DevBox | Local development environment |
| Build Agents | CI/CD pipeline runners |
| Deploy Agents | Specialized runners with production network access |
Production-Like Test Environments (PLTE)
PLTEs are isolated environments that emulate production characteristics, optimally ephemeral.
When the underlying infrastructure (such as PaaS/VM) doesn't support truly ephemeral environments, approximate ephemeral behavior by resetting dedicated slots between uses.
Connectivity note: A PLTE can be horizontally connected with other live systems, but such an environment cannot support automated testing in L3.
Horizontally connected PLTEs should only facilitate Exploration Activities - or specialized and human observed Extended Testing, as these systems are extremely fragile and can't support real deterministic testing.
PLTEs enable:
- Realistic testing without production risk
- Parallel testing for multiple topic branches
- Production IaC validation
- Performance and security testing in production-like conditions
Test Level Icons
Test levels are represented using color-coded ovals that indicate the execution environment and scope:
L0-L1: Unit/Component Tests
Blue ovals representing fast, in-process unit and component tests.
L2: Emulated System Tests
Yellow oval representing integration-level emulated system testing.
L3: In-Situ Vertical Tests
Orange oval representing in-situ vertical testing in PLTE environments.
L4: Production Tests
Red oval representing production testing and live verification.
HE2E: Horizontal E2E (Anti-Pattern)
Green rounded rectangle identifying shared pre-production anti-pattern.
References
- Overview - CD Model introduction
- The 12 Stages - Where each environment is used
- Environments - Environment types and zones
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