Sharing volumes between containers in Docker - Step-by-Step Execution

Process Flow - Sharing volumes between containers

Create Volume

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Start Container A with Volume

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Container A writes data

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Start Container B with same Volume

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Container B reads data

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Data shared via Volume

This flow shows how a volume is created and shared between two containers, allowing data written by one to be accessed by the other.

Execution Sample

Docker

docker volume create shared_data

docker run -d --name containerA -v shared_data:/data busybox sh -c "echo hello > /data/greeting.txt && sleep 3600"

docker run --rm -v shared_data:/data busybox cat /data/greeting.txt

Create a volume, run containerA writing a file to it, then run containerB to read the file from the same volume.

Process Table

Step	Command	Action	Result	Output
1	docker volume create shared_data	Create a named volume	Volume 'shared_data' created
2	docker run -d --name containerA -v shared_data:/data busybox sh -c "echo hello > /data/greeting.txt && sleep 3600"	Start containerA with volume mounted	ContainerA running, file written to /data/greeting.txt
3	docker run --rm -v shared_data:/data busybox cat /data/greeting.txt	Run containerB to read file from volume	ContainerB runs and reads file	hello
4	ContainerA stopped or removed	Volume persists independently	Data remains in volume

💡 ContainerB finishes reading and exits; volume data persists beyond container lifecycle.

Status Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
Volume 'shared_data'	Does not exist	Created	Contains greeting.txt with 'hello'	Accessible with 'hello' content	Remains with data after containers exit
ContainerA	Not running	Not running	Running, wrote file	Running	Stopped or removed
ContainerB	Not running	Not running	Not running	Runs, reads file	Exited

Key Moments - 3 Insights

Why does containerB see the file written by containerA?

Because both containers mount the same named volume 'shared_data', so data written by containerA is stored in the volume and accessible to containerB, as shown in execution_table step 3.

Does the volume get deleted when containerA stops?

No, the volume persists independently of containers. Even after containerA stops or is removed (step 4), the data remains in the volume for other containers to use.

What happens if containerB tries to read before containerA writes the file?

ContainerB would see no file or empty content because the volume is empty initially. The file appears only after containerA writes it, as shown in step 2 and 3.

Visual Quiz - 3 Questions

Look at the execution_table at step 3, what output does containerB produce?

A "hello"

B "greeting.txt not found"

C "" (empty output)

D Error: volume not found

💡 Hint

Check the 'Output' column in execution_table row for step 3.

At which step does the volume 'shared_data' get created?

A Step 2

B Step 1

C Step 3

D Step 4

💡 Hint

Look at the 'Action' column in execution_table for volume creation.

If containerA did not write the file, what would containerB see at step 3?

A Error: volume missing

B "hello"

C "greeting.txt not found" or empty output

D ContainerB would not start

💡 Hint

Refer to key_moments explanation about file presence before writing.

Concept Snapshot

Sharing volumes between containers:
- Create a named volume with 'docker volume create'
- Mount it in containers with '-v volume_name:/path'
- Data written by one container is accessible to others
- Volumes persist beyond container lifecycle
- Useful for sharing files or data between containers

Full Transcript

This visual execution shows how Docker volumes enable sharing data between containers. First, a volume named 'shared_data' is created. Then containerA starts with this volume mounted and writes a file 'greeting.txt' inside it. Next, containerB runs with the same volume mounted and reads the file, outputting 'hello'. The volume persists even after containers stop, allowing data sharing. Key points include volume creation, mounting, data persistence, and container independence from volume lifecycle.