{
  "lab": 4,
  "kind": "requirements, not runnable deployment",
  "required_for_grade_3": [
    {
      "role": "api",
      "count_min": 2,
      "student_implements": true,
      "persistent_local_state": false
    },
    {
      "role": "postgres",
      "purpose": "users/chats/membership/messages/metadata",
      "persistent_volume": true
    },
    {
      "role": "load_balancer",
      "public_entrypoint": true,
      "backend_readiness": true
    },
    {
      "role": "s3",
      "choose_one": [
        "MinIO",
        "SeaweedFS",
        "RustFS"
      ],
      "private_bucket": true,
      "persistent_volume": true
    }
  ],
  "optional_components": [
    {
      "role": "redis_or_valkey",
      "required_for_lab2_grade4": true,
      "note": "Choose one; if only store of sessions, configure durable persistence."
    }
  ],
  "rules": [
    "Choose Compose or Swarm for lab3+; do not need both.",
    "Never publish internal API replica ports in bypass of LB from lab3.",
    "Versions/digests must be fixed in implementation.",
    "Do not remove volumes in restart/failover checks.",
    "Document service names, healthchecks, bootstrap/migrations and credentials."
  ]
}