Dockerfile 中的“COPY”和“ADD”命令有什么区别?

Dockerfile 中的 COPYADD 命令之间有什么区别,我什么时候应该使用一个?

COPY <src> <dest>

COPY 指令将从 复制新文件并将它们添加到容器的文件系统中

ADD <src> <dest>

ADD 指令将从 <src> 复制新文件,并将它们添加到容器的文件系统中 <dest> 路径。

COPY copies a file/directory from your host to your image.

ADD copies a file/directory from your host to your image, but can also fetch remote URLs, extract TAR files, etc...

Use COPY for simply copying files and/or directories into the build context.

Use ADD for downloading remote resources, extracting TAR files, etc..

Source: https://nickjanetakis.com/blog/docker-tip-2-the-difference-between-copy-and-add-in-a-dockerile:

COPY and ADD are both Dockerfile instructions that serve similar purposes. They let you copy files from a specific location into a Docker image.

COPY takes in a src and destination. It only lets you copy in a local file or directory from your host (the machine building the Docker image) into the Docker image itself.

ADD lets you do that too, but it also supports 2 other sources. First, you can use a URL instead of a local file / directory. Secondly, you can extract a tar file from the source directly into the destination

A valid use case for ADD is when you want to extract a local tar file into a specific directory in your Docker image.

If you’re copying in local files to your Docker image, always use COPY because it’s more explicit.

ADD and COPY both have same functionality of copying files and directories from source to destination but ADD has extra of file extraction and URL file extraction functionality. The best practice is to use COPY in only copy operation only avoid ADD is many areas. The link will explain it with some simple examples difference between COPY and ADD in dockerfile