missing -f flag that indicates the name of the Dockerfile to use

Question

Missing -f flag in example that indicates the name of the Dockerfile to use for "Customize a Docker image to run your own web app" --> https://learn.microsoft.com/en-us/training/modules/intro-to-containers/4-create-custom-docker-image

Answer 1

This switch is optional. It is not required if Dockerfile resides in the current directory (which is implied by the trailing period)

As per https://docs.docker.com/reference/cli/docker/image/build/

By default the docker build command looks for a Dockerfile at the root of the build context. The -f, --file, option lets you specify the path to an alternative file to use instead. This is useful in cases that use the same set of files for multiple builds. The path must be to a file within the build context. Relative path are interpreted as relative to the root of the context.

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hth

Marcin