docker_info

Docker- Purpose:
	-develop/ship/run application
	-separates apps from infrastructure
	- deploy faster/ cycles of writing & running code decreases also

Docker- How
	-virtualization platfrom & workflows & tooling that help manage and deploy application

Docker- What
	-run apps in isolated containers
	-can run many containers on a host
	-containers are lightweight thus no extra load to hypervisor
		-hypervisor: software, firmware, hardware that creates and runs virtual machines
		-host machine: computer on which a hypervisor is running one  or more virtual machines
		-guest machine: where the hypervisor presents to the guest machine a virtual opening platform, and manages the execution of the guest operating systems.

-Docker- Containers
	-contains tooling and platform which can help with:
		--app into docker
		--distributing and shipping those containers to teams for development
		--deploying apps to prodution environment ie data center or cloud. 


-Docker - Use case:
	-allows devl. to work on containers before integration and deployment
	-write local code --> put into test envirn-->deploy

Docker -Components: 
	-open source container virtualization platform
	-Docker hub: platform for sharing and managing Docker containers


Docker-Architecture:
	-client/server 
	-Docker client talks to the Docker daemon (lifts, builds, runs, distributes docker containers)
	-Docker client and daemon can run on the same system
	-Docker client and daemon communicate via sockets or RESTful API

Docker daemon:
	- runs on a host machine; user doesn't interact with the daemon

Docker client:
	-primary UI to Docker.  It accepts commands from the user and communicates with the Docker daemon

Inside Docker:
	-Docker images,
	-Docker registries,
	Docker containers


Docker images:
	-read only template;
	-images are used to create Docker containers
	-Create, update, download docker images
	**are the BUILD compoenent of docker

Docker registries:
	-hold images
	-public/private stores upload or download images
	-public Docker registry is called DOCKER HUB (provides existing images for use)
	-you can create an image or use someone else's in the docker hub. 
	**Docker registry are distribution componenet of docker

Docker containers:
	-similar to directory
	- holds what's needed for an app to run
	-Each container is created from a docker image
	- containers can be run, started, stopped, moved, and deleted.
	-each container is isolated and secure app platform
	**run componenet of docker

Docker- main idea:
	-build docker images to hold app
	-create docker containers from those docker images to run app
	-share docker images via docker hub or own registry

How does Docker image work:
	-images contain layers. Layers are combined via union file system into a single image. 
	- Union file systems allow files and directories of sep. file systems (branches), to be transparently overlaid ==> single coherent file system. 

Relationship between images and speed:
	- Change of a Docker image, ie update an app to a new version, a new layer gets built.  The layer is added or updated.  There is NO NEED to distribute a whole new image. 

	virtual machines: have to replace the whole new image or entirely rebuild.  Images avoid that.

Base images:
	-ubuntu or fedora or personal

Building images from Base image are based on instructions:
	- run command
	-add file or directory
	-create env. variable
	- run process when launching container FROM image

	- These 4 instructions are stored in Dockerfile, a file. 
	-Request image--> Docker executes the Dockerfile--> image is built--> final image is returned

Docker registry:
	- store for docker images
	-Build docker image--> push public registry aka Docker Hub or your own registry running behind a firewall

	-Another way: use the docker client to pull down images and build containers for them

	-Docker hub: provides public  + private storage for images

How does Container work? 
	- Container contains: OS, user-added files, meta-data.  
	-Each container is built from an image
	-Image tells Docker waht the container holds (aka image talks to the Docker), what process to run when the container is launched, and a variety of other config. data. 
	-Image is read-only. 
	**- When dockers runs a container from an image, it adds a read-write layer on top of the image (via union file systems)
	-