Explanation
When you use docker, you're making and using pictures, containers, networks, volumes, plugins, and alternative objects. This section could be a brief summary of some of those objects.
IMAGESAn image is a read-only template with instructions for making a docker container. Often, a picture relies on another image, with some further customization. for instance, you'll build a picture that relies on the ubuntu image, however installs the Apache internet server and your application, still because the configuration details required to create your application run.
You may produce your own pictures otherwise you might solely use those created by others and printed in a registry. to create your own image, you produce a Dockerfile with a simple syntax for defining the steps needed to make the image and run it. every instruction in a Dockerfile creates a layer within the image. once you change the Dockerfile and rebuild the image, solely those layers that have modified square measure remodeled. this is often a part of what makes pictures therefore light-weight, small, and fast, when put next to alternative virtualization technologies.
CONTAINERSA instrumentality could be a runnable instance of a picture. you'll produce, start, stop, move, or delete a instrumentality victimization the docker API or user interface. you'll connect a instrumentality to at least one or a lot of networks, attach storage to that, or perhaps produce a brand new image supported its current state.
By default, a container is relatively well isolated from alternative containers and its host machine. you'll management however isolated a container's network, storage, or alternative underlying subsystems square measure from alternative containers or from the host machine.
A instrumentality is outlined by its image still as any configuration choices you offer to that once you produce or begin it. once a instrumentality is removed, any changes to its state that aren't hold on in persistent storage disappear.
Example docker run commandThe following command runs an ubuntu container, attaches interactively to your native command-line session, and runs /bin/bash.
$ docker run -i -t ubuntu /bin/bash
When you run this command, the subsequent happens (assuming you're victimization the default written account configuration):
* If you are doing not have the ubuntu image locally, docker pulls it from your designed registry, like you had run docker pull ubuntu manually.
* docker creates a new container, like you had run a docker container create command manually.
* docker allocates a read-write filesystem to the container, as its final layer. this permits a running container to make or modify files and directories in its native filesystem.
* dock-walloper creates a network interface to attach the docker to the default network, since you did not specify any networking choices. This includes assigning an IP address to the instrumentality. By default, containers will connect with external networks victimization the host machine's network connection.
* docker starts the container and executes /bin/bash. as a result of the container is running interactively and connected to your terminal (due to the -i and -t flags), you'll offer input using your keyboard whereas the output is logged to your terminal.
* when you type exit to terminate the /bin/bash command, the container stops however isn't removed.
you'll begin it once more or take away it.
SERVICESServices permit you to scale containers across multiple docker daemons, that all work along as a swarm with multiple managers and employees. every member of a swarm could be a docker daemon, and every one the daemons communicate victimization the docker API. A service permits you to outline the desired state, like the quantity of replicas of the service that has to be offered at any given time. By default, the service is load-balanced across all employee nodes. To the consumer, the docker API service seems to be one application. docker Engine supports swarm mode in docker one.12 and better.