CODEWITHSUNDEEP
imagedockerdockerfile
Carlos Alberto
Carlos Alberto

Reputation: 8635

Docker image hierarchy increases layer size?

In a scenario where a image extends from another image and so on, will this behavior increase the size of a custom image adding bigger layers?

For example: The image cbelleza/springboot-maven-s2i extends from alpine image, in this case the size of all dependencies would it be (115MB + 3.97MB) ?

$ docker images
REPOSITORY                      TAG                 IMAGE ID            CREATED             SIZE
cbelleza/springboot-maven-s2i   latest              3b92af74af2d        28 minutes ago      115MB
alpine                          latest              7328f6f8b418        2 weeks ago         3.97MB

Having a shared parent image that is referenced in multiple children images, does it reduce the size of those children images, or is better having a single image with all dependencies and commands included inside (apk, .gz, tar, etc)?

Upvotes: 1

Views: 713

Answers (1)

Robert
Robert

Reputation: 36903

Q. In a scenario where a image extends from another image and so on, will this behavior increase the size of a custom image adding bigger layers?

Each layer apport a differential amount of data, and does not repeat the previous ones.

Think an image as a layer plus metadata. Think layers as a tree of dependencies. The size of an image is the sum of its pointed layer plus each ancestor.

Let's say:

[layer A, image alpine] -> [layer B, no image] .-> [layer C, image app 1]
                                               |
                                                -> [layer D, image app 2]

Size of image app1 = size(C) + size(B) + size(A)

Size of image app2 = size(D) + size(B) + size(A)

Q. In this case, the size of all dependencies would it be (115MB + 3.97MB)?

Yes, but the real size in the disk will be much smaller due to they share layers.

Q. Having a shared parent image that is referenced in multiple children images, does it reduce the size of those children images, or is better having a single image with all dependencies and commands included inside (apk, .gz, tar, etc)?

You can have 1 base image of 1GB and 100 children images of 1MB, the total disk space will be (roughly) = 1GB + 100*1MB ~= 2GB. And not 1GB + 100*(1MB + 1GB).
However, the size of each child image is still 1GB + 1MB.

The same concept is applied in a docker registry, which will reuse any previously pushed layer.

Some docs here

Upvotes: 1

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