How to use "copy – link" to accelerate docker to build and optimize cache

COPY --link It's a new one BuildKit function , Can greatly accelerate your Docker Mirror construction . It works by copying files into separate image layers that do not depend on their predecessors . You can add new content to the image when there is no basic image on the system .

This function applies to 2022 year 3 Month as Buildx v0.8 Add... As part of . It is contained in Docker CLI edition 20.10.14 in , So if you are running the latest version , You should already be able to access .

In this paper , We will show its –link Function and explain how it works . We will also study some situations where it should not be used .

What is? “– link ”？

link It is available DockerfileCOPY New optional parameters of the instruction . It changes the way copies work by creating a new snapshot layer every time you use it .

routine COPY Statement to add a file to Dockerfile In the layer before them . The content of this layer needs to exist on your disk , So that new content can be merged into ：

FROM alpine
COPY my-file /my-file
COPY another-file /another-file

above Dockerfile Copy my-file Go to the layer generated by the previous command . After the instruction FROM, Image by Alpine The content of ：

bin/
dev/
etc/
...

First of all COPY Instructions generate an image , This includes coming from Alpine And my-file file ：