podman build --squash also squashes layers of base container

[mlschroe]

Description

podman build --squash squashes all layers into a single layer, whereas docker build --squash only squashes the new layers but keeps the layers from the base container. Is this difference intentional? It IMHO limits the usefulness of the --squash option quite a bit.

Steps to reproduce the issue:

1. podman build --squash

Describe the results you received:
The created container has only one layer.

Describe the results you expected:
The layers of the base container should be kept intact.

Output of rpm -q buildah or apt list buildah:

buildah-1.5-1.1.x86_64

Output of buildah version:

Version:         1.5
Go Version:      go1.11.1
Image Spec:      1.0.0
Runtime Spec:    1.0.0
CNI Spec:        0.4.0
libcni Version:  v0.7.0-alpha1
Git Commit:      87239ae7046ea3a25f644cd0789b3d6678dc144d
Built:           Fri Nov 23 12:00:00 2018
OS/Arch:         linux/amd64

Output of podman version if reporting a podman build issue:

Version:       0.11.1.1
Go Version:    go1.11.1
OS/Arch:       linux/amd64

[TomSweeneyRedHat]

@rhatdan @umohnani8 WDYT?

[rhatdan]

Definitely not intentional, we want to match Docker behaviour.

[pkubatrh]

Also hit this today while trying to see what to use instead of docker-squash in our workflow.

[vrothberg]

This one must have slipped over Christmas. Thanks for the report and the ping. We'll have a look.

[TomSweeneyRedHat]

@pkubatrh or @mlschroe do either of you have a Dockerfile that reproduces this handy? If not, I'll try to dig one up.

[TomSweeneyRedHat]

Never mind on the Dockerfile, I found a nice chunk on https://stackoverflow.com/questions/42786991/docker-squash-behavior

[rhatdan]

@nalind @TomSweeneyRedHat Whats the scoop on this one? Does some of the stuff @nalind is working on fix it?

[TomSweeneyRedHat]

Doesn't appear that @nanlind's changes fixed this, but I'll let him correct me.

[rhatdan]

@vrothberg @nalind @TomSweeneyRedHat Any progress on this?

[TomSweeneyRedHat]

Not that I know of, sigh, slipped off the radar.

[MaciejKucia]

This seems a requirements problem since original committer has assumed that all layers shall be squashed.

c806e6e#diff-b9ec73f876c8864b1fbdbf9fd96b4690

Reusing base layers makes a lot of sense, especially when dealing with many images based on common FROM (for example RedHat UBI).

[nalind]

Agreed, this is essentially a mislabeling based on a misread of what squash was supposed to be doing. A squashed result from docker build is equivalent to our --layers=false, but there's not really a good time to rename flags in the CLI and in the APIs.

[TomSweeneyRedHat]

@nalind is there something we can/should do with this or can we close this issue?

[mlschroe]

(Wouldn't --layers=false lead to slower builds as intermediate layers are no longer re-used in builds? I'd prefer squashing the layers at the end of the build.)

[TomSweeneyRedHat]

I've been playing today looking at the experimental --squash option in Docker and comparing it to the Buildah commands and these commands appear to be equivalent (Note buildah bud sets --layers to false by default, podman build sets --layers to true by default):

// Retain all layers, squash none.
docker build == buildah bud --layers=true == podman build

// Squash all new layers into 1 layer, retain old layers
docker build --squash == buildah bud == podman buildah --layers=false

// Squash all layers (old and new) into 1 layer.
buildah bud --layers=true --squash == podman build --squash # No Docker equivalent found.

Given that, I'm proposing that we simply switch the functionality of the --squash and the --layers=false functionality in the buildah bud command. That way our --squash will line up with Docker's and the --layers=false functionality would create only one layer.

The one point of concern with this proposal would be the default buildah bud command will leave only one layer. There would be no change in functionality for the default podman build command.

If we go forward with this proposal, @nalind suggests holding until we are ready for at least a new minor release (i.e 1.12.0) in both Buildah and Podman.

[graywolf-at-work]

Should this work? When I do buildah bud --squash and later try to pull the
images

+   $ docker pull shell-ci:xxx
xxx: Pulling from shell-ci
96470ff7e789: Pull complete
Digest: sha256:f52e76092abb54c485eab8dd5bf31579e10716e1673509fd64b83cb07dce3d14
Status: Downloaded newer image for shell-ci:xxx
shell-ci:xxx

but when I run buildah bud --layers=false, I do get:

+   $ docker pull shell-ci:xxx
xxx: Pulling from shell-ci
0329cb374ddf: Pull complete
425c89b8c674: Pull complete
4ca545ee6d5d: Pull complete
Digest: sha256:2d352967296e8dedb1b42e5feb650a3720dd5c925c6e6cdc5a3e825b7bbcb170
Status: Downloaded newer image for shell-ci:xxx
shell-ci:xxx

Dockerfiles are created in this order:

1. base (FROM scratch)
2. base-ci (FROM base)
3. shell-ci (FROM base-ci)

My buildah version is

+   $ buildah --version
buildah version 1.14.9 (image-spec 1.0.1-dev, runtime-spec 1.0.1-dev)

[rhatdan]

Could you see if Docker is having issues with OCI Images.

Build the image with --format docker and see if you have the same problems.