Day 03:Docker Data Persistence: Volumes vs Bind Mounts

Introduction

In containerized environments, data persistence is crucial to ensure that data is not lost when a container stops or restarts. Docker provides two primary methods for data persistence: volumes and bind mounts. This blog will explain both methods, their differences, and when to use each.

Understanding Docker Storage

When working with containers, the filesystem inside a container is ephemeral by default, meaning any data stored inside the container will be lost when the container is removed. To overcome this limitation, Docker provides two ways to persist data:

1. Volumes – Managed by Docker and stored in /var/lib/docker/volumes/ on the host.

2. Bind Mounts – Links a directory on the host system to a directory inside the container.

Volumes

What Are Docker Volumes?

Docker volumes are the preferred mechanism for persisting data in containers. They are managed entirely by Docker and offer better performance and flexibility compared to bind mounts.

Creating and Using Docker Volumes

Docker volumes store persistent data independent of container lifecycles. They are the preferred method for managing container data.

List Existing Volumes

Before creating a new volume, check the existing volumes:

docker volume ls

Create a New Volume

To create a dedicated volume:

docker volume create mongodb_volume

Run a MongoDB Container with a Volume

To run MongoDB with persistent storage:

docker run  -d --name mongodb -v mongodb_volume:/data/db -p 27017:27017 mongo:latest

Check Running Containers

To verify if the MongoDB container is running:

docker ps

Insert Data into MongoDB

Access the MongoDB shell inside the running container:

docker exec -it mongodb mongosh

Once inside, try the following:

show dbs;
use mydatabase;
db.hello.insertOne({ message: "Hello, Docker!" });
db.hello.find();

Stop and Restart the Container

Stop the MongoDB container:

docker stop mongodb

List stopped containers:

docker ps -a

Restart the MongoDB container:

docker start mongodb

Re-enter the MongoDB shell:

docker exec -it mongodb mongosh

Since we used a Docker volume, all inserted data remains intact after restarting

Advantages of Volumes

• Managed by Docker: Volumes are stored in a separate location from the host file system, making them more portable.

• Better Performance: Volumes are optimized for containerized workloads.

• Easy Backup & Restore: You can easily back up and restore volumes using Docker commands.

• Works Well with Swarm: Volumes integrate seamlessly with Docker Swarm for multi-container environments.

Bind Mounts

What Are Bind Mounts?

A bind mount directly links a directory from the host machine to a directory inside the container. Unlike volumes, bind mounts rely on the host’s filesystem structure.

Using Bind Mounts

Bind mounts provide a way to share files between the host machine and containers. They allow real-time synchronization but depend on the host's file structure.

Run a Container Without Network Access

To create an isolated container:

docker run --rm -d --name app1 -v /var/run/docker.sock:/var/run/docker.sock --network  none kiran2361993/troubleshootingtools:v1

Run a Container with Docker Socket Mounted

Mounting the Docker socket allows the container to communicate with the Docker daemon:

docker run -d -p 8000:8000 -p 9443:9443 --name portainer \
        --restart=always \
        -v /var/run/docker.sock:/var/run/docker.sock \
        -v portainer_data:/data \
        portainer/portainer-ce:2.11.1

Inspect the Running Container

To check details of the running container:

docker inspect troubleshootingtools

Look for the Mounts section to verify the bind mount configuration

Advantages of Bind Mounts

• Direct Access to Host Files: Allows seamless access to files from the host system.

• Useful for Development: Enables live code reloading when files change on the host.

• Simple and Flexible: Can mount any directory on the host machine.

Volumes vs Bind Mounts: Key Differences

Key Takeaways

• Volumes persist data across container lifecycles and are managed by Docker.

• Bind mounts allow direct access to host files but depend on the host system.

• Network isolation ensures containers run securely without external access.

Using these methods, you can efficiently manage containerized applications while ensuring data persistence and security.