Docker - Day5

Welcome to Day 5 of Docker series! So far, we’ve learned how to build, run, and network Docker containers. But what happens when your container needs to persist data?

In today’s blog, we’ll dive into:

• Why we need volumes

• Types of Docker volumes

• How volumes work under the hood

• How to create and manage volumes

• Best practices and real-world use cases

Why Do We Need Volumes?

By default, any data created inside a container is ephemeral—meaning it’s gone when the container is removed. But real-world apps (like databases, logging systems, etc.) need to persist data even after containers are stopped or recreated.

Volumes provide a solution by decoupling storage from the container lifecycle.

Docker Volumes

A Docker Volume is a storage mechanism managed by Docker itself, used to persist and share data across containers.

Think of volumes as a safe, independent space on your host (or remote) that lives outside of containers—but is accessible from them.

Types of Docker Volumes

Docker supports different types of volumes and mounts that allow containers to store and persist data.

1. Named Volumes

Volumes explicitly created and managed by Docker.

docker volume create myvolume

• Location on Host: /var/lib/docker/volumes/

✅ Use Cases:

• Databases

• Application persistent storage

• Easy sharing between containers

2. Anonymous Volumes

Volumes Docker creates without a specified name.

docker run -v /app/data myimage

• Volume name: Randomly generated (e.g., 6c5d1f3a99d59...)

• Difficult to manage manually

⚠️ Use Cases:

• Quick testing

• When you don’t need to reuse or manage volume outside the container

3. Bind Mounts

Mounts a specific path on the host to a path inside the container.

docker run -v /host/path:/container/path myimage

• Host-controlled, unlike volumes that Docker manages.

⚠️ Use Cases:

• Development (e.g., live sync code)

• Mounting configuration files from the host

⚠️ Limitations:

• Less portable

• Can break container isolation

• Prone to permission issues

4. tmpfs Mounts

Mounts a temporary file system in memory only (never written to disk).

docker run --tmpfs /app/tmp myimage

✅ Use Cases:

• Store sensitive data (e.g., tokens, keys)

• Temporary files like caches

• Performance-critical use cases (in-memory speed)

⚠️ Limitations:

• Data disappears after container stops

5. Volume Plugins (Third-Party Volumes)

Custom drivers that integrate with external storage backends (e.g., AWS EBS, NFS, NetApp).

docker volume create \
  --driver rexray/ebs \
  --name my-ebs-volume

✅ Use Cases:

• Enterprise-scale, distributed, or cloud storage

• Kubernetes/Swarm with persistent storage

Summary Table

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How to Work with Docker Volumes

1. Create a Volume

This creates a volume named mydata.

docker volume create mydata

2. Use Volume in a Container

Here, the MySQL container will store all data in the volume mydata—not inside the container itself.

docker run -d \
  --name mydb \
  -v mydata:/var/lib/mysql \
  mysql

3. Inspect Volumes

This shows mount point, driver info, usage, etc.

docker volume inspect mydata

4. Remove a Volume

docker volume rm mydata

Use Case: Persistent PostgreSQL

docker volume create pgdata

docker run -d \
  --name pg \
  -e POSTGRES_PASSWORD=mysecret \
  -v pgdata:/var/lib/postgresql/data \
  postgres

Stop and remove the container:

docker rm -f pg

Start a new one and reuse the volume:

docker run -d \
  --name pg2 \
  -e POSTGRES_PASSWORD=mysecret \
  -v pgdata:/var/lib/postgresql/data \
  postgres

You’ll find your database is still intact. 🎉

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Best Practices for Docker Volumes

• Use named volumes for clarity and reusability.

• Avoid bind mounts in production (security risks).

• Version control your volume definitions in docker-compose.yml.

• Backup volumes using docker run --rm -v mydata:/data busybox tar.

Docker Compose + Volumes Example

version: "3.8"
services:
  db:
    image: postgres
    volumes:
      - pgdata:/var/lib/postgresql/data
volumes:
  pgdata:

Run with:

docker compose up -d

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🚀 Happy Dockering!