Volumes, Bind Mounts, and Data Lifecycle

Container filesystems are ephemeral -- when you remove a container, everything inside it is deleted. If you are running a database, uploading files, or storing any data that matters, you must mount external storage. This module covers how.

Golden Rule

If you run a database without a volume, your data will be deleted when the container is removed.

How Storage Works in Docker

flowchart TD
    subgraph Host["Docker Host"]
        subgraph DockerArea["/var/lib/docker/volumes/"]
            Vol["Named Volume<br/>(managed by Docker)"]
        end
        subgraph UserArea["Any host path"]
            Bind["Bind Mount<br/>(your files)"]
        end
        RAM["RAM / tmpfs"]
    end

    subgraph Container
        D1["/var/lib/postgresql/data"]
        D2["/app/src"]
        D3["/tmp/cache"]
    end

    Vol -->|"Survives container deletion"| D1
    Bind -->|"Live sync with host"| D2
    RAM -->|"Lost on stop"| D3

    style Vol fill:#e8f5e9,stroke:#2e7d32
    style Bind fill:#e3f2fd,stroke:#1565c0
    style RAM fill:#fff3e0,stroke:#ef6c00

What You Will Learn

Lesson	What It Covers
Volumes vs Bind Mounts	When to use each storage type, with practical examples
Backup and Restore	Portable patterns for backing up and migrating volume data

Quick Decision Guide

Question	Answer
Is it a database or persistent app state?	Use a named volume
Is it source code during development?	Use a bind mount
Is it temporary data (cache, sessions)?	Use tmpfs
Is it a config file injected from the host?	Use a bind mount (read-only)

Prerequisites

• Understand containers and docker run (Module 4)
• Understand Docker networking basics (Module 5)