Welcome to our Docker tutorial! Today, we’ll address a common question: How do you include files from outside Docker’s build context using the “ADD” command in your Dockerfile?
According to Docker documentation, the path specified in the “ADD” command must be within the context of the build. This means you can’t use paths like “../something/something” since the initial step of a Docker build is to transmit the context directory (along with its subdirectories) to the Docker daemon.
Now, you might be wondering, “Do I have to restructure my entire project just to accommodate Docker?” The good news is, you don’t have to! If you prefer to keep all your Dockerfiles in the same sub-directory, there are alternative approaches.
One important note is that Docker does not currently support symlinks, as highlighted in issue #1676. So, if you were considering using symlinks to manage external files, that option may not be available.
A potential workaround involves incorporating a pre-build step to copy the necessary files into the Docker build context. By configuring your version control to ignore these files, you can maintain a cleaner project structure. While this may seem like an additional step, it can be an effective workaround to seamlessly integrate external files into your Docker build.
Stay tuned for more tips and tricks on optimizing your Docker workflows!
A practical solution to address this issue is to explicitly specify the Dockerfile separate from the build context using the -f flag.
For example, consider the following command, which grants the ADD command access to all files in your current directory:
docker build -f docker-files/Dockerfile .
In an update, Docker has introduced the capability to have the Dockerfile located outside the build context (fixed in version 18.03.0-ce). This enhancement allows you to execute a command like the following:
docker build -f ../Dockerfile .
This flexibility provides more options for organizing your Docker-related files and improves the overall workflow.