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POP

Introduction to docker

João Neves - [email protected]

June 2017

Objectives for today

  • Understand what docker does, its advantages and disadvantages.
  • Install docker
  • Run a command on a docker container
  • Customise a docker container
  • Debugging a running docker container
  • Introduction to docker_compose
  • Start/restart stop a set of containers

Docker

  • Containers
  • Union file-system

Docker vs Hardware Servers

  • Less requirements
  • Faster start of another container
  • Easier to replicate/scale

Docker vs Virtualization

  • Only runs linux apps
  • No overhead to isolate another OS
  • App vs Computer
  • Faster start of another container

Install docker

Running a command on a docker container

For running a docker container you need:

  • Docker installed
  • A docker image

Try this now: docker run hello-world

If you want, you can run a command instead of the default one:

docker run debian:jessie bash -c "echo Hello World"

This runs echo Hello World on a bash shell on Debian Jessie image. Can you change it to output something else?

Customising things

Running an nginx server with static content I

docker run --rm --name some-nginx -v /Users/joao/Sites:/usr/share/nginx/html:ro -d nginx

See if it's running with docker ps:

CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                  NAMES
af5d79b14a76        nginx               "nginx -g 'daemon ..."   18 hours ago        Up 18 hours         80/tcp                 some-nginx

Important things to note:

  • ID - you'll need this for all operations
  • PORTS - which ports are available, and which ports are they mapped to (ex: 0.0.0.0:8080->80/tcp)

Customising things

Running an nginx server with static content II

Try to access with http://localhost/ .

See if there's anything in the logs with docker logs <id>.

Stop it with docker stop <id>.

Customising things

Running an nginx server with static content III

docker run --rm --name some-nginx -v /Users/joao/Sites:/usr/share/nginx/html:ro -d -p 8080:80 nginx

Try to access with http://localhost:8080/ .

See if there's anything in the logs with docker logs <id>.

Debugging

docker ps

CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                  NAMES
af5d79b14a76        nginx               "nginx -g 'daemon ..."   18 hours ago        Up 18 hours         80/tcp                 some-nginx

Important things to note:

  • ID - you'll need this for all operations
  • IMAGE - image used for the container
  • COMMAND - the process that is running - if this process dies, so does the container
  • CREATED - when the container was created
  • STATUS - is it up or down? for how long? a failure to restart will constantly show seconds here
  • PORTS - which ports are available, and which ports are they mapped to (ex: 0.0.0.0:8080->80/tcp)
  • NAME - container name

Looking for a disappeared container? Use docker ps -a (all).

Debugging

docker logs

We've already seen docker logs <id>.

But you can see what's happening in realtime with docker logs -f <id>.

Inspect the container

docker exec -it <id> /bin/bash

This gives you a shell inside the container, with this you can inspect what's going on inside. Some containers don't have bash, in those cases try:

docker exec -it <id> /bin/sh

You can build your own docker container

  1. Write your own Dockerfile.
  2. Build the docker container.
  3. Run it.

Let's do a web server with a custom static page.

# Use an official nginx runtime as a base image
FROM nginx:latest

# Set the working directory to the static page dir
WORKDIR /usr/share/nginx/html

# Copy the current directory contents into the container at /usr/share/nginx/html
ADD . /usr/share/nginx/html

# Make port 80 available to the world outside this container
EXPOSE 80

# Run nginx when the container launches
CMD /usr/sbin/nginx -g 'daemon off;'

Build container

docker build -t tutorialsite .

Note the images being built in layers!

Run the container

docker run --rm -p 4000:80 tutorialsite

Now go to http://localhost:4000/

But when you want to launch multiple configurations...

there is docker-compose

You setup a configuration file like:

web:
  image: tutorialsite
  ports:
    - "4000:80"

Run:

docker-compose -f tutorial.cfg up -d

and check if it's working and respoding at http://localhost:4000/

docker-compose -f tutorial.cfg down

to cleanup

You can even use it to avoid creating images

web:
  image: nginx
  volumes:
   - .:/usr/share/nginx/html
  ports:
   - "4000:80"
  command: ['/usr/sbin/nginx', '-g', 'daemon off;']

Run:

docker-compose -f tutorial1.cfg up -d

and check if it's working and respoding at http://localhost:4000/

docker-compose -f tutorial1.cfg down

to cleanup

Or for multiple services

web:
  image: nginx
  volumes:
   - .:/usr/share/nginx/html
  ports:
   - "4000:80"
  command: ['/usr/sbin/nginx', '-g', 'daemon off;']
web1:
  image: nginx
  volumes:
   - .:/usr/share/nginx/html
  ports:
   - "4004:80"
  command: ['/usr/sbin/nginx', '-g', 'daemon off;']

Run:

docker-compose -f tutorial2.cfg up -d

and check if it's working and respoding at http://localhost:4000/ and http://localhost:4004/

docker-compose -f tutorial2.cfg down

to cleanup

More resources

Docker documentation: https://docs.docker.com/get-started/

Docker Hub: https://hub.docker.com/ (the default registry)

That's all folks!

Questions? Comments?