The pipeline
Continuous integration builds, tests, scans and produces one immutable artefact. Continuous delivery promotes that same artefact through environments, changing configuration only. If a build is remade per environment, you are not testing what you ship.
Deployment strategies
Rolling updates replace instances gradually. Blue-green keeps two full environments and switches traffic instantly, giving a clean rollback. Canary sends a small traffic slice to the new version and promotes on healthy metrics. Feature flags separate deployment from release entirely.
Rollback and safety
Every deploy needs a tested rollback path, database migrations must be backwards compatible (expand, migrate, contract), and pipelines need OIDC-federated credentials rather than stored cloud keys.