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Intro to Docker

Incredibly Fast, Lightweight, version-controlled

Linux Containers

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Docker

  • Docker was founded an Open Source project in 2013 as a way to provide extremely light weight Linux containers.
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Docker

  • Docker was founded an Open Source project in 2013 as a way to provide extremely light weight Linux containers.

  • In 2015, Docker formed the Open Container Initiative as a means to provide open source governance to the spread of Linux containers.

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Docker

  • Docker was founded an Open Source project in 2013 as a way to provide extremely light weight Linux containers.

  • In 2015, Docker formed the Open Container Initiative as a means to provide open source governance to the spread of Linux containers.

  • Docker (and Linux container technologies) are seeing widespread adoption across the inudstry and are used heavily in Cloud Native applications.

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Linux Containers

What are they?

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Linux Containers

What are they?

"A Linux® container is a set of processes that are isolated from the rest of the system, running from a distinct image that provides all files necessary to support the processes."

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Linux Containers

What are they?

"A Linux® container is a set of processes that are isolated from the rest of the system, running from a distinct image that provides all files necessary to support the processes."

  • Essentially, a Linux container is a standalone Linux machine that is running on top of an existing Linux OS.
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Linux Containers

What are they?

"A Linux® container is a set of processes that are isolated from the rest of the system, running from a distinct image that provides all files necessary to support the processes."

  • Essentially, a Linux container is a standalone Linux machine that is running on top of an existing Linux OS.

  • Docker gets some of its magic from using a Union file systems, UnionFS, which operates by creating layers.

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Linux Containers

An Example

You have a CentOS EC2 Instance runnning on AWS with Docker installed.

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Linux Containers

An Example

You have a CentOS EC2 Instance runnning on AWS with Docker installed.

This allows you to spin up a PostGIS container.

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Linux Containers

An Example

You have a CentOS EC2 Instance runnning on AWS with Docker installed.

This allows you to spin up a PostGIS container.

  • The PostGIS container has its own image.
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Linux Containers

An Example

You have a CentOS EC2 Instance runnning on AWS with Docker installed.

This allows you to spin up a PostGIS container.

  • The PostGIS container has its own image.
  • The PostGIS container has its own processes.
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Linux Containers

An Example

You have a CentOS EC2 Instance runnning on AWS with Docker installed.

This allows you to spin up a PostGIS container.

  • The PostGIS container has its own image.
  • The PostGIS container has its own processes.
  • The PostGIS container exposes port 5432.
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Linux Containers

Example Continued

You would also have the ability to spin up other images:

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Linux Containers

Example Continued

You would also have the ability to spin up other images:

  • An Elasticsearch image you could talk to on port 9300.
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Linux Containers

Example Continued

You would also have the ability to spin up other images:

  • An Elasticsearch image you could talk to on port 9300.
  • An GeoServer image you could talk to on port 8080.
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Linux Containers

Example Continued

You would also have the ability to spin up other images:

  • An Elasticsearch image you could talk to on port 9300.
  • An GeoServer image you could talk to on port 8080.
  • A Node image for a microserver on port 8001.
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Linux Containers

Example Continued

You would also have the ability to spin up other images:

  • An Elasticsearch image you could talk to on port 9300.
  • An GeoServer image you could talk to on port 8080.
  • A Node image for a microserver on port 8001.
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Why Linux Containers and Docker?

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Why Linux Containers and Docker?

Linux Containers are everything we ever wanted VMs to be and more...

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Why Linux Containers and Docker?

Linux Containers are everything we ever wanted VMs to be and more...

  • Incredibly fast spin up time. Docker prebakes images.
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Why Linux Containers and Docker?

Linux Containers are everything we ever wanted VMs to be and more...

  • Incredibly fast spin up time. Docker prebakes images.
  • Version Control. Docker allows images to be scripted.
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Why Linux Containers and Docker?

Linux Containers are everything we ever wanted VMs to be and more...

  • Incredibly fast spin up time. Docker prebakes images.
  • Version Control. Docker allows images to be scripted.
  • Replicable Environments. Docker images spin up the same everytime.
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Why Linux Containers and Docker?

Linux Containers are everything we ever wanted VMs to be and more...

  • Incredibly fast spin up time. Docker prebakes images.
  • Version Control. Docker allows images to be scripted.
  • Replicable Environments. Docker images spin up the same everytime.
  • Immutability. Create once, then throw away.
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Why Linux Containers and Docker?

Linux Containers are everything we ever wanted VMs to be and more...

  • Incredibly fast spin up time. Docker prebakes images.
  • Version Control. Docker allows images to be scripted.
  • Replicable Environments. Docker images spin up the same everytime.

  • Immutability. Create once, then throw away.

  • No install setups. Anyone can easily have the exact same setup running in prod.

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Union File Systems

VMs are BIG, bulky, and slow. Docker is lightweight and fast.

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Union File Systems

VMs are BIG, bulky, and slow. Docker is lightweight and fast.

  • UnionFS uses layers to provide copy on write storage.
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Union File Systems

VMs are BIG, bulky, and slow. Docker is lightweight and fast.

  • UnionFS uses layers to provide copy on write storage.

  • UnionFS excels when you assume that most files in a file system remain unchanged.

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Union File Systems

An Example

Imagine you have 10 CentOS containers running on your machine. Here is what you know is true:

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Union File Systems

An Example

Imagine you have 10 CentOS containers running on your machine. Here is what you know is true:

  • Each CentOS container is looking at the exact same files in their virtual filesystem.
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Union File Systems

An Example

Imagine you have 10 CentOS containers running on your machine. Here is what you know is true:

  • Each CentOS container is looking at the exact same files in their virtual filesystem.

  • Container A writes a new file to the /home directory. Container A writes a new layer to the virtual filesystem.

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Union File Systems

An Example

Imagine you have 10 CentOS containers running on your machine. Here is what you know is true:

  • Each CentOS container is looking at the exact same files in their virtual filesystem.

  • Container A writes a new file to the /home directory. Container A writes a new layer to the virtual filesystem.

  • Only Container A sees the new layer. The rest of the containers remain looking at the base image file system.

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Docker - How it works...

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Docker - How it works...

First: Dockerfile

  • A script that specifies the base image (Linux flavor) and what should be installed.
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Docker - How it works...

First: Dockerfile

  • A script that specifies the base image (Linux flavor) and what should be installed.

Second: Image

  • docker build "prebakes" your Dockerfile as an image so that it can be spun up quickly.
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Docker - How it works...

First: Dockerfile

  • A script that specifies the base image (Linux flavor) and what should be installed.

Second: Image

  • docker build "prebakes" your Dockerfile as an image so that it can be spun up quickly.

Third: Container

  • docker run creates a Linux container based on your image.
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First: Dockerfile

Dockerfile is the blue print for the Image that is used to create a container.

# the base image
FROM centos:7
# install commands
RUN yum -y update
RUN rpm -ivh http://dl.fedoraproject.org/pub/epel/6/i386/epel-release-6-8.noarch.rpm
# specify the port to be exposed
EXPOSE 8080
# run the application
CMD["python", "-m SimpleHTTPServer"]
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Second: Image

docker build runs the Dockerfile and "prebakes" an image.

$ docker build --tag example .
Sending build context to Docker daemon  68.61kB
Step 1/4 : FROM centos:7
7: Pulling from library/centos
af4b0a2388c6: Pull complete 
Digest: sha256:6247c7082d4c86c61b00f7f2e3edbf7f072a24aa8edc28b5b68b3de3101bc1ce
Status: Downloaded newer image for centos:7
 ---> ff426288ea90
 Step 2/4 : RUN yum -y update
 ...
$ docker images
REPOSITORY  TAG                 IMAGE ID            CREATED             SIZE
example     latest              6bb88ddf2b57        4 minutes ago       374MB
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Third: Container

docker run starts up a container of the specified image

$ docker run -i -t example
[root@f91976ba8452 /]# 
[root@f91976ba8452 /]# ls
anaconda-post.log  bin  dev  etc  home  lib  lib64  media  mnt  opt  proc  root  run  sbin  srv  sys  tmp  usr  var
$ docker ps 
CONTAINER ID  IMAGE     COMMAND     CREATED              STATUS    PORTS             NAMES
f91976ba8452  example   "/bin/bash" About a minute ago   Exited (0)   8 seconds ago   amazing_brown
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Common Docker Challenges

Pro - Docker provides a completely isolated environment.

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Common Docker Challenges

Pro - Docker provides a completely isolated environment.

  • Docker provides fresh machine everytime.

  • Setup is entirely scripted.

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Common Docker Challenges

Pro - Docker provides a completely isolated environment.

  • Docker provides fresh machine everytime.

  • Setup is entirely scripted.

Challenge - Sharing things with a Docker container.

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Common Docker Challenges

Pro - Docker provides a completely isolated environment.

  • Docker provides fresh machine everytime.

  • Setup is entirely scripted.

Challenge - Sharing things with a Docker container.

  • What if you need to set environment variables for your app?
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Common Docker Challenges

Pro - Docker provides a completely isolated environment.

  • Docker provides fresh machine everytime.

  • Setup is entirely scripted.

Challenge - Sharing things with a Docker container.

  • What if you need to set environment variables for your app?

  • What if you're working locally and you want the container to run the local version of your code?

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Solving Common Docker Challenges

Environment Variables

  • Environment variables can be injected into the container using the -e VAR=VALUE format on the docker run command.
docker run -e PORT=80 some_image
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Solving Common Docker Challenges

Injecting Files

  • In development, use the --mount command to have a file inside of the container write directly through to a host file.
docker run --mount type=bind,source="$(pwd)"/build/libs,\
target=/app
  • This mount an executable jar file in {project root}/build/libs into the container at the /app directory.
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Common Docker Challenges

Pro - Docker environments are designed to run a single process.

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Common Docker Challenges

Pro - Docker environments are designed to run a single process.

  • The machine setup stays relatively simple.
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Common Docker Challenges

Pro - Docker environments are designed to run a single process.

  • The machine setup stays relatively simple.

Challenge - Running multi server systems.

  • How would you run the web app as a Docker container and connect to the database or Elasticsearch?
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Solving Common Docker Challenges

Connecting Docker Containers

Docker Compose allows you to connect multiple docker containers together.

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Solving Common Docker Challenges

Connecting Docker Containers

Docker Compose allows you to connect multiple docker containers together.

  • Docker Compose uses a config file to manipulate Docker's built in networking capabilities.
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Solving Common Docker Challenges

Connecting Docker Containers

Docker Compose allows you to connect multiple docker containers together.

  • Docker Compose uses a config file to manipulate Docker's built in networking capabilities.

  • Docker Compose allows you to spin up entire applications and not just individual machines

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Solving Common Docker Challenges

Docker Compose

This a docker-compose.yml 

version: "2"
services:
  es:
    image: elasticsearch
  web:
    image: prakhar1989/foodtrucks-web
    command: python app.py
    ports:
      - "5000:5000"
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Solving Common Docker Challenges

Breaking down the docker-compose.yml

version: "3.3"
services: # list all of the containers
  web:  
    image: prakhar1989/foodtrucks-web
    command: python app.py
    ports:
      - "5000:5000"

is equivalent to

$ docker run -p 5000:5000 example-image python.app.py

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Docker Best Practices

Docker containers are designed to run one process.

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Docker Best Practices

Docker containers are designed to run one process.

  • The CMD line in your Dockerfile indicates the one process that should be running.
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Docker Best Practices

Docker containers are designed to run one process.

  • The CMD line in your Dockerfile indicates the one process that should be running.

  • The container should only have one responsibility, one main job.

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Docker Best Practices

Docker containers are designed to run one process.

  • The CMD line in your Dockerfile indicates the one process that should be running.

  • The container should only have one responsibility, one main job.

  • Using Docker Compose multiple Docker containers can be linked together (i.e. web app container and a database container).:

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Docker Best Practices

Docker containers are designed to be immutable.

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Docker Best Practices

Docker containers are designed to be immutable.

  • All of the container setup is scripted in the Dockerfile.
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Docker Best Practices

Docker containers are designed to be immutable.

  • All of the container setup is scripted in the Dockerfile.

  • Immutability means a consistently known state. Update the Dockerfile, throw away all of your containers and spin up new ones.

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Docker Best Practices

Avoid storing application data on the Docker container.

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Docker Best Practices

Avoid storing application data on the Docker container.

  • Remember Docker is essentially version controlling the file system. It increases the size of your container.
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Docker Best Practices

Avoid storing application data on the Docker container.

  • Remember Docker is essentially version controlling the file system. It increases the size of your container.
  • In development, use the mount flag to write or reference directly to the host machine.
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Docker Best Practices

Avoid storing application data on the Docker container.

  • Remember Docker is essentially version controlling the file system. It increases the size of your container.
  • In development, use the mount flag to write or reference directly to the host machine.
  • In production, logs should stream to a log aggregation service.
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Common Docker Commands

There are several commands you need to know:

  • docker build - creates an image based on a Dockerfile
  • docker run - creates a container based on an image
  • docker images - lists all available images
  • docker stop - turns off a container
  • docker rm - deletes an image
  • sudo docker exec -i -t docker_id /bin/bash - jump in shell of existing server
  • docker --help - look up all of the commands you don't know
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Docker Commands

docker build

Options

  • docker build --tag someName - specifies "someName" as the name of your image.
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Docker Commands

docker build

Options

  • docker build --tag someName - specifies "someName" as the name of your image.

Other useful commands:

  • docker images - lists all images currently on your machine.
  • docker rmi someName - deletes the image named "someName"
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Docker Commands

docker run

Options

docker run someName - Create a container from the someName image.

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Docker Commands

docker run

Options

docker run someName - Create a container from the someName image.

docker run -i -t someName - Start a container with the terminal as the main process

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Docker Commands

docker run

Options

docker run someName - Create a container from the someName image.

docker run -i -t someName - Start a container with the terminal as the main process

docker run -p 80:8080 someName - Publish port 8080 of the container on port 80 of 127.0.0.1 (the machine running Docker)

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Docker Commands

docker run

Options

docker run someName - Create a container from the someName image.

docker run -i -t someName - Start a container with the terminal as the main process

docker run -p 80:8080 someName - Publish port 8080 of the container on port 80 of 127.0.0.1 (the machine running Docker)

docker run --name myContainer someName - Create a container named "myContainer"

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Docker Commands

Other helpful commands

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Docker Commands

Other helpful commands

docker ps - list all running containers

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Docker Commands

Other helpful commands

docker ps - list all running containers

docker ps -a - list all containers

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Docker Commands

Other helpful commands

docker ps - list all running containers

docker ps -a - list all containers

docker stop someName - stop the container named "someName"

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Docker Commands

Other helpful commands

docker ps - list all running containers

docker ps -a - list all containers

docker stop someName - stop the container named "someName"

docker rm someName - delete the container named "someName"

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Docker Commands

Other helpful commands

docker ps - list all running containers

docker ps -a - list all containers

docker stop someName - stop the container named "someName"

docker rm someName - delete the container named "someName"

docker logs someName - view all of the written to STDOUT for "someName"

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Questions?

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29 / 29

Docker

  • Docker was founded an Open Source project in 2013 as a way to provide extremely light weight Linux containers.
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