{
  "id": "docker-port-publish-mcq",
  "title": "Works Inside, Unreachable Outside",
  "category": "Containers",
  "isolation_type": "shared_namespace",
  "difficulty": "Medium",
  "type": "mcq",
  "weight": 4,
  "description": "## Works Inside, Unreachable Outside\n\nA web server container is confirmed healthy — `docker exec <container> curl localhost:80` succeeds from inside it. But `curl http://localhost:8080/` from the HOST fails to connect. The container was started with plain `docker run -d myapp` (no other flags). What's most likely missing?",
  "options": [
    { "id": "a", "text": "The image itself is broken" },
    { "id": "b", "text": "A `-p 8080:80` port-publish flag was never set when the container was created, so nothing on the host maps to the container's port 80" },
    { "id": "c", "text": "The container needs more memory" },
    { "id": "d", "text": "DNS is misconfigured" }
  ],
  "correct_option": "b",
  "explanation": "Working correctly INSIDE the container proves the application itself is fine — the failure is specifically that the host has no mapping to the container's internal port. Port publishing (`-p hostPort:containerPort`) must be set at container creation time; without it, the container's ports are only reachable from other containers on the same Docker network, never from the host.",
  "hints": [],
  "setup_commands": [],
  "default_namespace": "default",
  "teardown_commands": []
}