Why registries store and distribute images in Docker - Visual Breakdown

Process Flow - Why registries store and distribute images

Developer builds image

↓

Push image to registry

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Registry stores image

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User pulls image from registry

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User runs container from image

This flow shows how a developer creates a container image, pushes it to a registry, which stores it, and then users pull and run containers from that image.

Execution Sample

Docker

docker build -t myapp:1.0 .
docker push myapp:1.0
docker pull myapp:1.0
docker run myapp:1.0

Build an image, push it to a registry, pull it back, and run a container from it.

Process Table

Step	Action	Image State	Registry State	Result
1	Build image 'myapp:1.0'	Image created locally	Registry empty or unchanged	Image ready locally
2	Push 'myapp:1.0' to registry	Image still local	Image stored in registry	Image uploaded successfully
3	Pull 'myapp:1.0' from registry	Image local (may overwrite)	Image stored in registry	Image downloaded locally
4	Run container from 'myapp:1.0'	Image local	Image stored in registry	Container running from image
5	End	Image local	Image stored in registry	Process complete

💡 All steps complete; image stored and distributed via registry for reuse.

Status Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	Final
Local Image	None	myapp:1.0 built	myapp:1.0 present	myapp:1.0 present	myapp:1.0 present	myapp:1.0 present
Registry Image	None	None	myapp:1.0 stored	myapp:1.0 stored	myapp:1.0 stored	myapp:1.0 stored
Container	None	None	None	None	Running from myapp:1.0	Running from myapp:1.0

Key Moments - 3 Insights

Why do we push images to a registry instead of just keeping them locally?

Pushing images to a registry allows sharing and reuse by others or on other machines, as shown in step 2 where the image moves from local to registry.

What happens when you pull an image that already exists locally?

Pulling updates or overwrites the local image with the registry version if different, as seen in step 3 where the image is downloaded again.

Why do we need registries to distribute images?

Registries act like a central library storing images so anyone can download and run them, enabling easy distribution and version control, demonstrated in steps 2 and 3.

Visual Quiz - 3 Questions

Look at the execution table, what is the state of the registry after step 2?

A Image is only local, not in registry

B Registry is empty

C Image 'myapp:1.0' is stored in the registry

D Container is running in the registry

💡 Hint

Check the 'Registry State' column at step 2 in the execution table

At which step does the container start running?

A Step 1

B Step 4

C Step 2

D Step 3

💡 Hint

Look at the 'Result' column for when the container is running

If the image was never pushed to the registry, what would happen at step 3?

A Pull would fail because image is not in registry

B Pull would succeed and download image

C Container would run without image

D Image would be built automatically

💡 Hint

Refer to the 'Registry State' and 'Action' columns at step 3

Concept Snapshot

Docker registries store container images centrally.
Developers push images to registries to share.
Users pull images from registries to run containers.
Registries enable easy distribution and version control.
Images exist locally and in registries separately.
Pushing and pulling sync images between local and registry.

Full Transcript

This visual execution shows how container images move from a developer's local machine to a registry and then to users. First, the developer builds an image locally. Then, they push it to a registry, which stores the image centrally. Other users can pull the image from the registry to their local machines. Finally, users run containers from the pulled images. This process allows sharing and reuse of container images across different machines and teams. The execution table tracks each step's state changes for the image locally, in the registry, and container status. Key moments clarify why registries are needed and what happens when pulling images. The quiz tests understanding of registry states and container running steps.