Docker Objects

Dockerfile

• It is a simple text file with a set of commands or instructions.
• These commands/instructions are executed successively to perform actions on the base image to create a new docker image.
• It will help you create custom Docker images.
• Each instruction present in the docker file, represents a layer of the docker image.

Docker Images

• A Docker image is made up of a collection of files that bundle together that are essential for the application.
• It is read-only templates that you build from a set of instructions written in a Docker file.
• The docker build command builds an image from a Dockerfile by reading the instructions from a Dockerfile.
• Images define both what you want your packaged application and its dependencies to look like what processes to run when it’s launched.
• Docker images act as a set of instructions to build a Docker container, like a template.

Docker Containers

• Containers are the structural units of Docker, which are used to hold the entire package that is needed to run the application.
• A Docker container is a virtualized run-time environment of the docker images.
• In other words, we can say that the image is a template, and the container is the instance of the template.
• These containers are compact, portable units in which you can start up an application quickly and easily.

Docker Volume

• Docker volume enables the persistence and sharing of the container’s data.
• Docker volume is the Docker host’s directory mounted inside the container that allows the container to write container data into the host volumes.
• The mechanism is presented in the following diagram:

Docker network

• Docker networking enables a user to link a Docker container to as many networks as we require.
• Docker Networks are used to provide complete isolation for Docker containers.
• Docker contains the following network drivers -

Bridge — Bridge is a default network driver for the container. It is used when multiple dockers communicate with the same docker host.

Host — It is used when we don’t need network isolation between the container and the host.

None — It disables all the networking.

Overlay — Overlay offers Swarm services to communicate with each other. It enables containers to run on different Docker hosts.

Macvlan — Macvlan is used when we want to assign MAC addresses to the containers.