The Commands
Examine the major commands to work with containerizing an application.
We'll cover the following
Docker commands
-
docker image build
is the command that reads a Dockerfile and containerizes an application. The-t
flag tags the image, and the-f
flag lets you specify the name and location of the Dockerfile. With the-f
flag, it is possible to use a Dockerfile with an arbitrary name and in an arbitrary location. The build context is where your application files exist, and this can be a directory on your local Docker host or a remote Git repo. -
The
FROM
instruction in a Dockerfile specifies the base image for the new image you will build. It is usually the first instruction in a Dockerfile and a best-practice is to use images from official repos on this line. -
The
RUN
instruction in a Dockerfile allows you to run commands inside the image. EachRUN
instruction creates a single new layer. -
The
COPY
instruction in a Dockerfile adds files into the image as a new layer. It is common to use theCOPY
instruction to copy your application code into an image. -
The
EXPOSE
instruction in a Dockerfile documents the network port that the application uses. -
The
ENTRYPOINT
instruction in a Dockerfile sets the default application to run when the image is started as a container. -
Other Dockerfile instructions include
LABEL
,ENV
,ONBUILD
,HEALTHCHECK
,CMD
, and more.
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