What is the difference between the 'COPY' and 'ADD' commands in

ghz 8months ago ⋅ 133 views

What is the difference between the 'COPY' and 'ADD' commands in a Dockerfile?

What is the difference between the COPY and ADD commands in a Dockerfile, and when would I use one over the other?

COPY <src> <dest>

The COPY instruction will copy new files from <src> and add them to the container's filesystem at path <dest>

ADD <src> <dest>

The ADD instruction will copy new files from <src> and add them to the container's filesystem at path <dest>.

Answers

The COPY and ADD commands in a Dockerfile are used to copy files from the host machine into the container during the image build process. While they have similar functionalities, there are some differences between them:

COPY:

  • Syntax: COPY <src> <dest>
  • Purpose: Copies files or directories from the host machine to the container's filesystem at the specified destination path (<dest>).
  • Use Cases: Typically used for simple file copying operations where you only need to copy files from the host to the container.
  • Behavior: COPY only supports copying local files or directories from the host machine. It does not support URLs or extraction of compressed files.

ADD:

  • Syntax: ADD <src> <dest>
  • Purpose: Similar to COPY, it also copies files or directories from the host machine to the container's filesystem at the specified destination path (<dest>).
  • Use Cases: Provides additional functionality beyond COPY. It can also fetch remote URLs and automatically extract compressed files.
  • Behavior:
    • Besides copying local files or directories, ADD can also copy files from remote URLs, which are automatically downloaded and placed in the destination directory.
    • If <src> is a URL or a local tar archive, it will be automatically extracted to <dest>.
    • Because of the additional functionality, ADD is considered more powerful but may also introduce unexpected behavior or security risks if not used carefully.

When to Use Each:

  • Use COPY when you need to perform simple file copying operations and you want to ensure clarity and explicitness in your Dockerfile.
  • Use ADD when you need the additional functionality it provides, such as copying from remote URLs or automatically extracting compressed files. However, be cautious with ADD to avoid unintentional side effects and potential security risks.

Best Practices:

  • Use COPY by default unless you specifically need the extra functionality provided by ADD.
  • Be cautious with ADD to avoid unnecessary complexity and potential security vulnerabilities, especially when dealing with remote URLs or automatically extracting files.
  • If you only need to copy files from the host machine to the container, COPY is generally preferred for its simplicity and explicitness.
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