I follow this K8s tutorial, and in the middle of the file, there is the following instruction:
12. Now let’s build an image, giving it a special name that points to our local cluster registry.
$docker build -t 127.0.0.1:30400/hello-kenzan:latest -f applications/hello-kenzan/Dockerfile applications/hello-kenzan
I don't understand why do you need to point to the dockerfile using -f applications/hello-kenzan/Dockerfile.
In the man of docker build:
-f, --file=PATH/Dockerfile
Path to the Dockerfile to use. If the path is a relative path and you are
building from a local directory, then the path must be relative to that
directory. If you are building from a remote URL pointing to either a
tarball or a Git repository, then the path must be relative to the root of
the remote context. In all cases, the file must be within the build context.
The default is Dockerfile.
So -f is to point to the dockerfile, but we already gave the path of the dockerfile in the end of build command - docker build ...applications/hello-kenzan, so why do you need to write it twice? am I missing something?
The reason for this is because he probably had multiple files called Dockerfile and using -f tells the docker to NOT use the Dockerfile in the current directory (when there's one) but use the Dockerfile in the applications/hello-kenzan instead.
While in THIS PARTICULAR example it was unnecessary to do this, I appreciate the tutorial creator to show you an option to use PATH and point the -f at specific place to show you (the person who wants to learn) that it is possible to use Dockerfiles that are not in PATH (i.e when you have multiple dockerfiles you want to create your builds with or when the file is not named Dockerfile but e.g myapp-dockerfile)