04. Accessing Docker Containers & Using Volumes

Accessing Docker Containers & Using Volumes

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Prerequisites

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1. Accessing a Running Container

✔️ Using docker exec

docker exec -it <container_id> bash

• -it → interactive terminal
• bash → shell inside container

Example:

docker exec -it 2a8dda3 bash

👉 Allows you to:

• Inspect files
• Run commands
• Debug application

Command	Purpose
docker run	Create + start new container
docker exec	Enter already running container

2. Volume (Persistent Storage)

Feature	Bind Mount (-v path:path)	Volume (-v name:path)
Location	User-defined	Docker-managed
Use case	Development	Production
Portability	Low	High

2-1. Why Data Disappears (Important)

Containers are ephemeral

• When container is deleted → data is gone
• Because data lives in writable layer

2-2. Solution: Volume (Persistent Storage)

✔️ What is a Volume?

A volume is a way to store data outside the container

• Data persists even if container is deleted
• Can be shared across containers

✔️ Basic Syntax (Bind Mount)

docker run -v <host_path>:<container_path> <image>

✔️ Example

docker run -v C:\data:/app/data ubuntu

👉 Meaning:

Host (C:\data)  ←→  Container (/app/data)

• Changes in container → reflected on host
• Changes in host → reflected in container

✔️ Create volume (Volume)

docker volume create my-volume

✔️ Use volume

docker run -v my-volume:/app/data ubuntu

Docker manages storage internally

[ Host Disk ]
   └── /var/lib/docker/volumes/my-volume/_data   ← Real Data
        or \\wsl$\docker-desktop-data\data\docker\volumes\my-volume

                ↑ mount

[ Container ]
   └── /app/data   ← Container