Docker Volumes

9. Docker Volumes

💾 What is a Volume?

Problem: When a container is deleted, all data inside it is gone forever.

Analogy: A container is like a hotel room. When you check out, the room is cleaned — everything left behind is gone. A volume is like a storage locker outside the hotel — you can store things there, check out, and come back later to retrieve them.

Volumes solve data persistence in Docker.

📦 Types of Storage in Docker

Type	Description	Use Case
Named Volume	Docker manages the storage location	Databases, persistent data
Bind Mount	You specify the exact host path	Development (sync code)
Anonymous Volume	Docker manages, no name	Temporary, discarded after use
tmpfs Mount	Stored in host memory only	Sensitive temporary data

💽 Storage Diagram

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  <!-- Background -->
  <rect width="700" height="320" fill="#f8f9fa" rx="12"/>
  <text x="350" y="28" text-anchor="middle" font-size="14" font-weight="bold" fill="#222">Docker Storage Types</text>

  <!-- Host Machine -->
  <rect x="20" y="50" width="660" height="250" rx="10" fill="#fff8e1" stroke="#f57f17" stroke-width="2"/>
  <text x="350" y="73" text-anchor="middle" font-size="12" font-weight="bold" fill="#e65100">Host Machine Filesystem</text>

  <!-- Named Volume -->
  <rect x="40" y="88" width="180" height="100" rx="8" fill="#e8f5e9" stroke="#2e7d32" stroke-width="1.5"/>
  <text x="130" y="110" text-anchor="middle" font-size="12" font-weight="bold" fill="#1b5e20">Named Volume</text>
  <text x="130" y="128" text-anchor="middle" font-size="10" fill="#388e3c">/var/lib/docker/volumes/</text>
  <text x="130" y="144" text-anchor="middle" font-size="10" fill="#388e3c">my-data/_data</text>
  <rect x="55" y="155" width="150" height="24" rx="4" fill="#a5d6a7"/>
  <text x="130" y="172" text-anchor="middle" font-size="10" fill="#1b5e20">Docker Managed ✓</text>

  <!-- Bind Mount -->
  <rect x="255" y="88" width="180" height="100" rx="8" fill="#e3f2fd" stroke="#1565c0" stroke-width="1.5"/>
  <text x="345" y="110" text-anchor="middle" font-size="12" font-weight="bold" fill="#0d47a1">Bind Mount</text>
  <text x="345" y="128" text-anchor="middle" font-size="10" fill="#1565c0">/home/user/myapp</text>
  <text x="345" y="144" text-anchor="middle" font-size="10" fill="#1565c0">(your chosen path)</text>
  <rect x="270" y="155" width="150" height="24" rx="4" fill="#90caf9"/>
  <text x="345" y="172" text-anchor="middle" font-size="10" fill="#0d47a1">You Control Path ✓</text>

  <!-- Anonymous Volume -->
  <rect x="470" y="88" width="180" height="100" rx="8" fill="#fce4ec" stroke="#880e4f" stroke-width="1.5"/>
  <text x="560" y="110" text-anchor="middle" font-size="12" font-weight="bold" fill="#880e4f">Anonymous Vol</text>
  <text x="560" y="128" text-anchor="middle" font-size="10" fill="#880e4f">/var/lib/docker/volumes/</text>
  <text x="560" y="144" text-anchor="middle" font-size="10" fill="#880e4f">a3b4c5d6.../_data</text>
  <rect x="485" y="155" width="150" height="24" rx="4" fill="#f48fb1"/>
  <text x="560" y="172" text-anchor="middle" font-size="10" fill="#880e4f">Random ID (Temporary)</text>

  <!-- Container -->
  <rect x="200" y="215" width="300" height="60" rx="8" fill="#f3e5f5" stroke="#6a1b9a" stroke-width="2"/>
  <text x="350" y="240" text-anchor="middle" font-size="12" font-weight="bold" fill="#4a148c">Container</text>
  <text x="350" y="258" text-anchor="middle" font-size="10" fill="#6a1b9a">/data  /app  /tmp</text>

  <!-- Arrows from volumes to container -->
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  <line x1="345" y1="190" x2="345" y2="213" stroke="#1565c0" stroke-width="1.5" stroke-dasharray="5,3"/>
  <line x1="560" y1="190" x2="450" y2="225" stroke="#880e4f" stroke-width="1.5" stroke-dasharray="5,3"/>
</svg>

🔧 Volume Commands

# === NAMED VOLUMES ===

# Create a named volume
docker volume create my-data

# List all volumes
docker volume ls

# Inspect a volume
docker volume inspect my-data

# Remove a volume
docker volume rm my-data

# Remove all unused volumes
docker volume prune

# Use a named volume when running a container
docker run -v my-data:/data/db mongo

# === BIND MOUNTS ===

# Mount current directory into container
docker run -v $(pwd):/app node:18

# Mount specific host path
docker run -v /home/user/myapp:/app node:18

# Read-only bind mount
docker run -v $(pwd):/app:ro node:18

# === ANONYMOUS VOLUMES ===

# Docker creates a random volume
docker run -v /data mongo

💡 Real-World Volume Use Case

# Run PostgreSQL with persistent data
docker run -d \
  --name postgres-db \
  -e POSTGRES_PASSWORD=secret \
  -e POSTGRES_DB=myapp \
  -v postgres-data:/var/lib/postgresql/data \
  -p 5432:5432 \
  postgres:15

# Even if you delete and recreate the container, data persists:
docker rm -f postgres-db
docker run -d \
  --name postgres-db \
  -e POSTGRES_PASSWORD=secret \
  -v postgres-data:/var/lib/postgresql/data \
  -p 5432:5432 \
  postgres:15
# ✅ Your database data is still there!