Docker Note

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1. Install on CentOS

Requires Kernel 3.0+, and update library before install

Install on CentOS Guidance

2. Introduction

2.1 Usage

container, isolate applications
packaged with all its dependencies and libraries(environment)

2.2 Workflow

  1. Get codes and dependencies tio container
  2. Configure network or storage(optional)
  3. Upload builds to a registry
  4. Swarm cluster and scale(optional)
  5. Deploy

A kind of namespace tool?
Concentrates on 调度 and 编排 ？

2.3 Structure

2.3.1 Components

  • Docker Client
    UI, communicate with Daemon
  • Docker Daemon
    sits on host, answers request
  • Docker Index
    centralized registry

2.3.2 Elements

  • Docker Containers
    responsible for app’s running, including OS, user files and meta data
  • Docker Images
    read-only templates, help launch Docker containers
  • DOckerFile
    file housing instructions, help automate image creation

Docker Structure

2.3.3 Support by OS

  • Namespaces
    first level of isolation
  • Control Groups
    a part of LXC(Linux Control), an OS level virtualization method for running multiple isolated Linux systems(containers)
  • UnionFS
    file system

docker namespaces –> namespaces –> physical memory ?

2.3.4 Docker Registry

Shelve progress:

Docker入门教程（四）Docker Registry

And official doc and guide:
RA_CI with Docker

Hello world in a container

3. Official getstarted

3.1 starter

  1. run a hello world to check
    run: create & run a container
    hello-world: image to load into the container
    option -rm means ..

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    $ sudo docker run hello-word

  2. list all containers
    image: is a filesystem and parameters to use at runtime
    doesn’t have state and never changes
    Container: a running instance of an image

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    $ docker ps -a

  3. Find image in Docker Hub
    Docker Hub

  4. Build your own image

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    $ touch Dockerfile
    Contents:
    FROM docker/whalesay:latest
    RUN apt-get -y update && apt-get install -y fortunes
    CMD /usr/games/fortune -a | cowsay

    Then build an image from Dockerfile:
    $ docker build -t docker-whale .

    The procedure:
    1. Docker check things available: send context to Docker daemon
    2. load image defined in FROM
    3. RUN
    4. CMD

  5. Push image to Hub/repository
    sign up for Docker Hub
    create a repository for image
    push image to online

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    $ docker tag 292ad9b8d884 skyvoice/docker-whale:latest
    $ docker login
    $ docker push skyvoice/docker-whale

3.2 Manage images

  1. list images

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    $ docker images

  2. remove image

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    $ docker rmi -f 7d9495d03763
    $ docker rmi -f docker-whale

  3. daemonized container

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    query Docker daemon, list containers
    [docker@dockermount docker]$ docker ps
    CONTAINER ID        IMAGE               COMMAND                  CREATED              STATUS              PORTS               NAMES
    657b964200ef        ubuntu              "/bin/sh -c 'while tr"   About a minute ago   Up About a minute                       suspicious_kilby
    Or add flag -l, show only last container started.
    add flag -a, show all containers.
    add flag -q, show container ids only.

    We can use NAME of this container to query execution logs:
    [docker@dockermount docker]$ docker logs suspicious_kilby
    It looks inside the container, and shows the standard output of a container.

    And to stop this container:
    [docker@dockermount docker]$ docker stop suspicious_kilby

3.3 Run container

  1. Run command

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    $ docker run ubuntu /bin/echo 'hello ubuntu'

  2. Run interactive container

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    $ docker run -t -i ubuntu /bin/bash

-t assigns a pseudo-tty or terminal inside the container
-i grabd teh standard input[STDIN] of the container, allow you to make an interactive connection

3.4 Run application

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See port mapping:
$ docker port #name 5000

View logs:
$ docker logs -f #name

List processes:
$ docker top #name

Stop and remove
$ docker stop #name
$ docker rm #name

Remove all container:
$ docker rm $(docker ps -aq)

Note

Removing a container is final(cannot undo)

3.5 Network container

  1. Name your container:

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    $ docker run -d -P --name web training/webapp python app.py

  2. Docker provides two network drivers: bridge(Default) and overlay.
    Use network sub command to list them:

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    $ docker network ls

  3. View Network info of container:

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    [docker@dockermount ~]$ docker network inspect bridge

  4. Create your own network:

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    [docker@dockermount ~]$ docker network create -d bridge my-bridge-net

  5. Connect your newly running container to this network:

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    [docker@dockermount ~]$ docker network connect my-bridge-net web

  6. Then try ping each other in two containers:

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    $ docker exec -it db bash

Note

You can attach many network to a container, but two containers can reach other only in the same network

3.6 Manage data in container

Data volume

A specially-designed directory, within one or more containers that bypasses the Union File System(operates by creating layers, making them very lightweight and fast)
Designed to persist data, even container is removed

Add a data volume to container:

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[docker@dockermount ~]$ docker run -d -P --name web -v /webapp training/webapp python app.py

To be continue….

3.7 Docker Certicates for both daemon and client

For detailed procedures:
Protect the Docker daemon socker

Note

By default, Docker runs via a non-networked Unix socket. Config using an HTTP socket if you need communicate.

$HOST in the doc is the ip addr of daemon server, not dns

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$ echo subjectAltName = IP:10.200.157.84,IP:10.200.157.48,IP:127.0.0.1 > extfile.cnf

To integrate with Spring boot on Windows, plz install docker-install.exe and DockerToolbox-1.12.2.exe. They will auto create a vm with installed docker.
[Update 2016-11-15]
Boot2docker cannot push images into Hub, for unknown reason.
Use Linux Docker daemon server instead.

Connect to docker VM by docker/tcuser

4. Notice

Advantages

  1. containers are immutable
    same image tested by QA will reach production environment with same behaviour

  2. container are lightweight
    memory footprint of it is small

  3. container are fast
    DO NOT treat containers as virtual machines

Mentra

  1. containers are disposable/ephemeral

Try to Avoid

  1. dont store data
  2. dont ship application in two pieces
  3. dont crate large images
    dont install unnecessary packages or run “update”
  4. dont use a single layer image
    use layered filesystem, username definition, runtime installation, configuration and then application
    easier to recreate, manage and distribute
  5. dont create images from running containers
  6. dont use only “lastest” tag
    like “SNAPSHOT”, unsafe and irretrievable
  7. dont run more than on process in a single container
  8. dont store credentials in image
    use environment variables
  9. dont run processes as root
  10. dont rely on IP addresses
    use environment variables

Reference:
10 things to avoid in docker containers

Benefits

  1. Try new Tech at low cost
    Using images in the Hub

  2. Test and run with consistency

  3. Build a dev environment

To Be continue

Manage data in container