使用Python Docker SDK构建镜像时COPY文件失败，如何确保文件在构建上下文？

The Problem #

I've got this file structure:

Dockerfile
apps/
└── myapi/
    └── api-1.0.8.json

Here's my Dockerfile:

FROM mybase
# Simply need to update config file
ARG asset_api=myapi
ARG asset_api_version=1.0.8
COPY $PWD/apps/${asset_api}/api-${asset_api_version}.json /api.json

Building with the Docker CLI works perfectly fine, but when I run my Python Docker SDK code:

client.images.build(path="./", tag='myimage:tag', buildargs={'asset_api': 'myapi', 'asset_api_version': '1.0.8'}, use_config_proxy=True)

I hit this error:

docker.errors.BuildError: COPY failed: stat /var/lib/docker/tmp/docker-builder289614590/apps/myapi/api-1.0.8.json: no such file or directory

How can I make sure the file is properly included in the build context?

The Fix #

The issue is that you're using $PWD in your Dockerfile's COPY command—and that's a mistake, even if it seemed to work with the CLI. Here's why and how to fix it:

Why This Breaks with the SDK #

When you run a Docker build, Docker sends your entire build context (in this case, the current directory ./) to the Docker daemon, which runs the build in a temporary directory on its end.

• With the CLI, your local shell might be expanding $PWD to your local working directory before sending the Dockerfile to the daemon. That's why it worked by accident.
• With the Python SDK, the $PWD variable gets passed directly to the daemon, where it resolves to the daemon's temporary build directory (like /var/lib/docker/tmp/docker-builder...). Since your apps folder isn't in that directory, the COPY fails.

The Correct Dockerfile #

Remove the $PWD prefix—Docker COPY paths are always relative to the root of your build context:

FROM mybase
# Simply need to update config file
ARG asset_api=myapi
ARG asset_api_version=1.0.8
COPY apps/${asset_api}/api-${asset_api_version}.json /api.json

Quick Checks to Ensure It Works #

1. Double-check that your Python script is running from the same directory that contains the Dockerfile and apps folder. You can verify this with:

   import os
   print(os.getcwd()) # Should output the path to your project root
   

2. Make sure there are no typos in your build args or file paths—even a single character mismatch will cause this error.

内容的提问来源于stack exchange，提问作者kosta