What is the .dockerfile extension?

Dockerfile

A Dockerfile is a text document that contains all the commands a user could call on the command line to assemble an image. Using docker build users can create an automated build that executes several command-line instructions in succession. Docker images are the basis of containers. An Image is an ordered collection of root filesystem changes and the corresponding execution parameters for use within a container runtime. An image typically contains a union of layered filesystems stacked on top of each other. An image does not have state and it never changes.More on

Dockerfile extension

A Dockerfile has no extension . if your using docker on docker on windows use notepad ++ to create a dockerfile while saving select “All type “ and save the file name as “Dockerfile”.

Mongodb/Dockerfile

About Docker

Docker is the company driving the container movement and the only container platform provider to address every application across the hybrid cloud. Today’s businesses are under pressure to digitally transform but are constrained by existing applications and infrastructure while rationalizing an increasingly diverse portfolio of clouds, datacenters and application architectures. Docker enables true independence between applications and infrastructure and developers and IT ops to unlock their potential and creates a model for better collaboration and innovation. More on

It appears that "*.dockerfile" is simply an alternative to the conventional "Dockerfile" name. This is perhaps useful if you want to keep a collection of dockerfiles in the same directory. Note the -f/--file option in docker help build:

-f, --file string Name of the Dockerfile (Default is 'PATH/Dockerfile')

In other words, you are not required to use the name "Dockerfile", and the VSCode extension will correctly syntax-highlight any file ending in ".dockerfile".

What worked for me was to save the file in VS Code as a Dockerfile. But, you need to remove the .dockerfile extension that VS Code puts on it before running the $docker-compose up command: