In this section, we will explain the syntax or the format of Dockerfile. A Dockerfile is made up of instructions, comments, and empty lines, as shown here:

# Comment

INSTRUCTION arguments

The instruction line of Dockerfile is made up of two components, where the instruction line begins with the instruction itself, which is followed by the arguments for the instruction. The instruction could be written in any case, in other words, it is case-insensitive. However, the standard practice or convention is to use uppercase in order to differentiate it from the arguments. Let's take another look at the content of Dockerfile in our previous example:

FROM busybox:latest
CMD echo Hello World!!

Here, FROM is an instruction which has taken busybox:latest as an argument, and CMD is an instruction which has taken echo Hello World!! as an argument.

The comment line in Dockerfile must begin with the # symbol. The # symbol after an instruction is considered as an argument...