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docker push

Definition

The CLI command used to upload a locally built Docker image to a remote Docker registry (like Docker Hub or AWS ECR).

Explain Like I'm New

Uploading your finished blueprint to the cloud so other computers can download it.

Real World Example

You finish writing code on your laptop. You build the image. You type `docker push myusername/my-app:v2`. Docker uploads the layers to the internet. Now your boss can pull the image and test it.

Common Use Cases

  • •CI/CD pipelines
  • •Image distribution

Interview Questions

basic

  • What happens if you run `docker push` before running `docker login`?

intermediate

  • If an image has 10 layers, and you only changed 1 line of code, does `docker push` upload all 10 layers again?

Flash Cards

Question

Push without login?

Click to reveal answer
Answer

Docker will throw an 'Access Denied / Unauthorized' error because it doesn't know who you are.

Question

Upload all layers?

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Answer

No! Docker is smart. It checks the Registry, sees that the first 9 layers are already uploaded, and only uploads the tiny 1 new layer. This makes pushing updates incredibly fast.