How to set up the same Docker cache behavior during build on Ubuntu as it is on Windows? - linux

Question

We have such Dockerfile:
FROM alpine:latest as step1
RUN echo "STEP1"
FROM alpine:latest as step2
RUN echo "STEP2"
FROM step1 as step3
RUN echo "STEP3"
On Windows (or on WSL2) we have such results for building multi-stage images.
Building all steps on Windows:
$ docker build .
[+] Building 0.2s (7/7) FINISHED
=> [internal] load build definition from Dockerfile 0.0s
=> => transferring dockerfile: 32B 0.0s
=> [internal] load .dockerignore 0.1s
=> => transferring context: 2B 0.0s
=> [internal] load metadata for docker.io/library/alpine:latest 0.0s
=> [step1 1/2] FROM docker.io/library/alpine:latest 0.0s
=> CACHED [step1 2/2] RUN echo "STEP1" 0.0s
=> CACHED [step3 1/1] RUN echo "STEP3" 0.0s
=> exporting to image 0.1s
=> => exporting layers 0.0s
=> => writing image sha256:38ba33425558f5373099ad59aa187456c38b3f5eab14a60fdbb3cb7b1c484392 0.0s
Use 'docker scan' to run Snyk tests against images to find vulnerabilities and learn how to fix them
Building Step 2 on Windows:
$ docker build --target step2 .
[+] Building 0.5s (6/6) FINISHED
=> [internal] load build definition from Dockerfile 0.0s
=> => transferring dockerfile: 32B 0.0s
=> [internal] load .dockerignore 0.0s
=> => transferring context: 2B 0.0s
=> [internal] load metadata for docker.io/library/alpine:latest 0.0s
=> CACHED [step2 1/2] FROM docker.io/library/alpine:latest 0.0s
=> [step2 2/2] RUN echo "STEP2" 0.3s
=> exporting to image 0.0s
=> => exporting layers 0.0s
=> => writing image sha256:855f35039a5a902e1d33111fc781f748955f8b3cad7fb56d6eb420fc5d2fa55b 0.0s
Use 'docker scan' to run Snyk tests against images to find vulnerabilities and learn how to fix them
Docker version on Windows:
$ docker version
Client:
Cloud integration: 1.0.17
Version: 20.10.7
API version: 1.41
Go version: go1.16.4
Git commit: f0df350
Built: Wed Jun 2 12:00:56 2021
OS/Arch: windows/amd64
Context: default
Experimental: true
Server: Docker Engine - Community
Engine:
Version: 20.10.7
API version: 1.41 (minimum version 1.12)
Go version: go1.13.15
Git commit: b0f5bc3
Built: Wed Jun 2 11:54:58 2021
OS/Arch: linux/amd64
Experimental: false
containerd:
Version: 1.4.6
GitCommit: d71fcd7d8303cbf684402823e425e9dd2e99285d
runc:
Version: 1.0.0-rc95
GitCommit: b9ee9c6314599f1b4a7f497e1f1f856fe433d3b7
docker-init:
Version: 0.19.0
GitCommit: de40ad0
While on Ubuntu we have slightly different results.
Building all steps on Ubuntu:
$ docker build .
Sending build context to Docker daemon 2.048kB
Step 1/6 : FROM alpine:latest as step1
---> d4ff818577bc
Step 2/6 : RUN echo "STEP1"
---> Using cache
---> ca7b2711269c
Step 3/6 : FROM alpine:latest as step2
---> d4ff818577bc
Step 4/6 : RUN echo "STEP2"
---> Using cache
---> 50668d3ea1c2
Step 5/6 : FROM step1 as step3
---> ca7b2711269c
Step 6/6 : RUN echo "STEP3"
---> Using cache
---> f529239cd29a
Successfully built f529239cd29a
Building Step 2 on Ubuntu:
$ docker build --target step2 .
Sending build context to Docker daemon 2.048kB
Step 1/4 : FROM alpine:latest as step1
---> d4ff818577bc
Step 2/4 : RUN echo "STEP1"
---> Using cache
---> ca7b2711269c
Step 3/4 : FROM alpine:latest as step2
---> d4ff818577bc
Step 4/4 : RUN echo "STEP2"
---> Using cache
---> 50668d3ea1c2
Successfully built 50668d3ea1c2
Docker version on Ubuntu:
$ docker version
Client: Docker Engine - Community
Version: 20.10.7
API version: 1.41
Go version: go1.13.15
Git commit: f0df350
Built: Wed Jun 2 11:56:38 2021
OS/Arch: linux/amd64
Context: default
Experimental: true
Server: Docker Engine - Community
Engine:
Version: 20.10.7
API version: 1.41 (minimum version 1.12)
Go version: go1.13.15
Git commit: b0f5bc3
Built: Wed Jun 2 11:54:50 2021
OS/Arch: linux/amd64
Experimental: false
containerd:
Version: 1.4.6
GitCommit: d71fcd7d8303cbf684402823e425e9dd2e99285d
runc:
Version: 1.0.0-rc95
GitCommit: b9ee9c6314599f1b4a7f497e1f1f856fe433d3b7
docker-init:
Version: 0.19.0
GitCommit: de40ad0
As you can see Docker Desktop (Windows) skips unneeded stages while Docker on Ubuntu builds them. The Docker Engine versions are the same.
For complex multi-stage images, the caching behavior the Docker on Windows can save a lot of build time comparing to the one on Ubuntu.
How to make Docker on Ubuntu behave the same way with cache as on Windows?

Answer 1

I found the answer by myself. On Ubuntu we need to enable BuildKit by DOCKER_BUILDKIT=1. See https://docs.docker.com/engine/reference/builder/#buildkit
In this case, the behavior on both platforms is the same.