Dockerfile

Dockerfile is a text document containing all the commands that the docker images need to get built. A docker image gets built by running all the docker command-line instructions mentioned in Dockerfile.

The docker build command is used to build an image from the Dockerfile and a context. And, context set of files of any PATH or URL.

docker build Syntax:

$ docker build .

Here, build is run by docker daemon, not by CLI. and (.) refers to the current directory as build context.

You can also refer to Dockerfile which is not in the project root directory as:

$ docker build -f /path/to/a/Dockerfile .

You can also use tag -t for a new image to be tagged, to do so run the following:

$ docker build -t sagar/demoapp .

Dockerfile Format

Format of Dockerfile:

# Your comment here
INSTRUCTION arguments

Note: Dockerfile must begin with a FROM instruction.

Example

FROM Image_Name

# Comment line starts with hash(#) sign
RUN echo 'Hello World'
RUN echo "Hello \\
		World"

Here, both RUN command instructions’ output will be the same.

Output:

Hello World