{
  "id": "docker-container-storage",
  "title": "Prove Data Survives a Container's Death — With a Volume",
  "category": "Containers",
  "isolation_type": "shared_namespace",
  "difficulty": "Medium",
  "type": "task",
  "weight": 6,
  "description": "## Prove Data Survives a Container's Death — With a Volume\n\nA container's own writable layer is disposable — data written there disappears when the container is destroyed. A named VOLUME is different.\n\n**Your task:**\n\n1. Create a named volume: `docker volume create storage-lab-vol`\n2. Run a container named `storage-lab-app` from `alpine:3.19` (keep it running with `sleep 3600`), mounting the volume at `/data`\n3. Write a file `/data/file.txt` containing exactly `persisted-data`, inside the container\n4. Destroy the container completely (`docker rm -f storage-lab-app`)\n5. Recreate it with the SAME name, SAME image, and the SAME volume mount\n6. Confirm `/data/file.txt` still contains `persisted-data` — proving the volume, not the container, is what actually held the data",
  "hints": [
    {
      "title": "Creating and mounting a volume",
      "body": "`-v <volume-name>:<path-in-container>` mounts a named volume at a path inside the container — data written there lives in the volume, independent of the container's own lifecycle.",
      "command": "docker volume create storage-lab-vol\ndocker run -d --name storage-lab-app -v storage-lab-vol:/data alpine:3.19 sleep 3600\ndocker exec storage-lab-app sh -c 'echo persisted-data > /data/file.txt'"
    },
    {
      "title": "Destroying and recreating",
      "body": "Removing the container does NOT remove the volume — recreating a container with the same `-v` flag reattaches the exact same data.",
      "command": "docker rm -f storage-lab-app\ndocker run -d --name storage-lab-app -v storage-lab-vol:/data alpine:3.19 sleep 3600\ndocker exec storage-lab-app cat /data/file.txt"
    }
  ],
  "setup_commands": [
    { "command": "docker rm -f storage-lab-app 2>/dev/null; docker volume rm storage-lab-vol 2>/dev/null; true" },
    { "command": "docker pull alpine:3.19" }
  ],
  "validation": {
    "commands": [
      { "description": "storage-lab-vol volume exists", "command": "docker volume inspect storage-lab-vol --format '{{.Name}}' 2>/dev/null", "expected_output": "storage-lab-vol", "match": "exact" },
      { "description": "storage-lab-app is running and mounts the volume at /data", "command": "docker inspect storage-lab-app --format '{{range .Mounts}}{{.Name}}:{{.Destination}} {{end}}' 2>/dev/null", "expected_output": "storage-lab-vol:/data", "match": "contains" },
      { "description": "the data genuinely survived a container destroy/recreate cycle", "command": "docker exec storage-lab-app cat /data/file.txt 2>/dev/null", "expected_output": "persisted-data", "match": "exact" }
    ]
  },
  "default_namespace": "default",
  "teardown_commands": [
    { "command": "docker rm -f storage-lab-app 2>/dev/null; docker volume rm storage-lab-vol 2>/dev/null; true" }
  ]
}