# Release Engineering & Continuous Delivery
- Treat every commit as a deployable artifact.
- Use CI to run tests and build artifacts; use CD to push to staging/production.
- Pin versions, sign artifacts, and audit changes.
- Release trains > hero deploys: small batches, fast feedback.

# 11 Factor Apps (12 Factor methodology adapted)
1. Codebase: one repo per service, tracked in version control.
2. Dependencies: explicit manifests, lockfiles, isolated environments.
3. Config: env vars/secrets outside code.
4. Backing services: attach databases/queues as resources.
5. Build/run separation: immutable artifacts, separate runtime.
6. Processes: stateless, share nothing, push state out.
7. Port binding: self-contained HTTP service.
8. Concurrency: scale by process model.
9. Disposability: fast startup, graceful shutdown.
10. Dev/prod parity: avoid one-off configs.
11. Logs/logging: treat logs as event streams.

# Microservices Architecture
- bounded context per service
- async communication where possible
- API contracts + versioning
- independent deployability
- observability: metrics, traces, structured logs