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Containers

Virtual Machines vs Containers

  • Virtual Machines:
    • Mimics a complete server. Has libraries, drivers, the OS, and the application
    • Run on a hypervisor, which runs on the host OS
    • A lot of duplication between the guest VMs caused by running the same binaries, wasting server resources
  • Containers:
    • Virtual instances share a single host OS system, libraries, drivers, and binaries
    • More memory efficient than VM
    • Operating System-Level Virtualization
    • Function of hypervisor is handled by the container engine (i.e. Docker)
    • Built in layers of images.
      • An image is a lightweight package that includes the code, runtime, libraries, environment variables, and config files
      • Container is an instance of an image

Docker

Containers

  • Dockerfiles:
    • Specifies the image.
    • Defines what happens inside of the container
    • Exposes network ports
    • Defines environment variables
  • docker run [image]: Creates a container from an instance
  • docker build [path]: Creates an images from a Dockerfile
  • docker images
  • docker ps
  • docker stop [container id]
  • docker rmi [image]
  • Pushing to registry
    • docker login
    • docker tag <image> username/repository:tag
    • docker push [image] username/repository:tag
    • Defaults to Docker Registry

Services

  • "A container in production"
  • Codifies the way an image is run, in docker-compose.yml
    • (i.e. Which ports it uses, Number of replicas on the container to run, etc)
  • docker stack ls
  • docker stack deploy -c [compose-file] [app name]
  • docker stack rm [app_name]
  • docker ps [app_name]
  • A swarm is a group multi-container of services being run on multiple machines
    • Also used to refer to the group of machines running Docker
  • A swarm manager is used to control the swarm
    • Strategies for running the containers within the swarm is specified the Compose file
    • Only swarm managers can execute commands and authorize other machines to join swarm
    • Enabling swarm mode makes the current machine the swarm manager
    • Machines can be virtual or physical
    • docker swarm init -creates the swarm manager
    • docker join
  • Any IP of a node is the swarm can be used to access the app because they all participate in a routing mesh (aka each node has a load balancer)
  • docker-machine create --driver [driver] [name]
  • docker-machine ssh "cmd"
  • docker-machine scp file [name]:[path] - copy file
  • docker-machine stop [name]
  • docker-machine rm [name]

Stack

  • A group of interrelated services that share dependencies and are scaled together