Running a Docker Based Environment With Vagrant

The end result will be a development environment which will only require vagrant up to setup a complete Docker-based environment. The components of this environment are:

• VM running Linux with Docker installed.
• Separate Docker containers for Rails, PostgreSQL and Redis.
• A shared folder linked to the Docker container so you can carry on editing Rails code on your development machine as you do now, and see those changes instantly reflected on http://localhost:3000.
• A simple interface for running all the normal Rails commands (rake db:migrate, rails c etc) in the Docker environment.

http://www.talkingquickly.co.uk/2014/06/rails-development-environment-with-vagrant-and-docker/

Docker

Generalities

Useful tutorial links:

• http://blog.flux7.com/blogs/docker/docker-tutorial-series-part-3-automation-is-the-word-using-dockerfile

Container vs Image

Images are containers in a certain state. Say you installed ubuntu 14.04 on a virtual machine, updated the aapt-get definitions and installed curl, essetial-packages and ruby-build.

All these changes can be saved as an image, which allows you to quickly download it and add the read-write layer on top of it and start your container. Once you add the read-write layer on top of an image, this image becomes a container.

Once your container is an a state that you would wish to preserve for duplication, commit your changes and the container is saved as an image.

Useful Docker Commands

Building Image from Dockerfile

• running sudo docker will reveal a list of options that can be used. build is the option we're looking for in order to create an image from a Dockerfile.
• sudo docker build -t ouruser/sinatra:v2 .. We've specified our docker build command and used the -t flag to identify our new image as belonging to the user ouruser, the repository name sinatra and given it the tag v2. We've also specified the location of our Dockerfile using the . to indicate a Dockerfile in the current directory.
• https://docs.docker.com/articles/dockerfile_best-practices/

Container Linking

We will link a pythen web container to a postgres one:

• download the postgres db image, name it as db and create a container: sudo docker run -d --name db training/postgres
• download the python web app image, name it as web, assign the ports, link it to the db container and run it:sudo docker run -d -P --name web --link db:db training/webapp python app.py. This will link the new web container with the db container you created earlier. The --link flag takes the form --link name:alias, where name is the name of the container we're linking and alias is an alias for the link name.
• running sudo docker inspect -f "{{ .HostConfig.Links }}" web should show you that the 2 containers are linked.

For some reason I was unable to run the sudo docker inspect -f "{{ .HostConfig.Links }}" web command and get the expected result. However, when you run a docker web container and enter the console, you'll be able to see that the 2 containers are linked as expected:

• run docker container and enter console: sudo docker run -t -i --rm --name web2 --link db:db training/webapp /bin/bash
• once the container is loaded check for the links:
  • run cat /etc/hosts.
  • run apt-get install -yqq inetutils-ping && ping db. Successful ping requests to the db container should be displayed. Exit the ping command by pressing ctrl + c
  • check the environment variables (env). You should see a series of db related variables, like DB_NAME, DB_PORT_5432_TCP_ADDR, DB_PORT, DB_PORT_5432_TCP, DB_PORT_5432_TCP_PORT, DB_PORT_5432_TCP_PROTO.

Data Containers

default is read-write, but read-only can be specified...

Adding a Data Volume Container

• create a volume data container: sudo docker create -v /dbdata --name dbdata training/postgres doesn't work, as there is no create anymore in the docker options.
• create PostgreSQL container that use the above created data container: sudo docker run -d --volumes-from dbdata --name db1 training/postgres
• add another container: sudo docker run -d --volumes-from dbdata --name db2 training/postgres
• check the status of the containers created: sudo docker ps

Backup and Restore Data Volumes

In order to create backups, we'll launch a container that adds a backups folder and creates a backup of the /dbdata folder:

• sudo docker run --volumes-from dbdata -v $(pwd):/backup ubuntu tar cvf /backup/backup.tar /dbdata
• create a new container and run bash: sudo docker run -v /dbdata --name dbdata2 ubuntu /bin/bash
• untar the backup created earlier by running: sudo docker run --volumes-from dbdata2 -v $(pwd):/backup busybox tar xvf /backup/backup.tar

https://docs.docker.com/userguide/dockervolumes/ https://medium.com/@ramangupta/why-docker-data-containers-are-good-589b3c6c749e