Story

Amazon Web Services is good and I love it because it’s easy to use, flexible and cost-effective.

But, at a point, at least for some companies, AWS becomes too clunky and too expensive.

That’s what is happening to BlackCitrus.

At this moment, we have four onging rails projects and they all have their own staging server, namely four EC2 instances (m3.medium). And they are all running 24x7. However, the utilization of those staging servers are really not much at all.

We recently initialized another rails project and we decided to limit our spend on AWS. However we still want all our applications are running 24x7 and don’t want to downsize the instance because of the poor performanace of small EC2 instances.

Docker to the rescue

What is Docker

Software Container

Docker is a tool that can package an application and its dependencies into a virtual container that can run on any Linux server.

In a way, Docker is a bit like a virtual machine. But unlike a virtual machine, rather than creating a whole virtual operating system, Docker allows applications to use the same Linux kernel as the system that they’re running on and only requires applications be shipped with things not already running on the host computer.

Why Docker

1. Easy Setup

What you’ll need is just one linux server runs Docker and a Dockerfile for each of your projects. Maybe an extra docker-compose.yml file if your application requires multiple containers.

2. Portability

Docker containers are independent from the host version of Linux Kernel, platform distribution or deployment model. They can be easily transfered to another machine that runs Docker, and executed there without compatibility issues.

3. App Isolation

By using containers, resources can be isolated, services restricted, and processes provisioned to have an almost completely private view of the operating system with their own process ID space, file system structure, and network interfaces. Docker lets you safely run multiple applications on the same cloud instance by abstracting and isolating their dependencies.

4. Lightweight, minimal overhead, high utilization

Docker images are typically very small and docker containners also require much less overhead - really no more expensive than a process. You can easily spin up 1000’s of docker containers on an ordinary PC. By deploying multiple Dockerized applications on to a single cloud instance, you can get much closer to achieving 100% utilization.

How docker changes things

Before Docker

  1. Create an new EC2 intance every time when you initialize an new project
  2. Install dependencies (i.e. ruby, mysql, redis). Nomarlly we do this by using Chef .
  3. Setup the deployment tool (i.e. Capistrano)

After Docker

  1. Create an EC2 instance (only once) and install Docker
  2. Dockerize the application by adding a Dockerfile and docker-compose.yml (if required)

What’s Next

The new rails app is now running smoothly in a docker container on a m3.medium EC2 instance. And we’ll migrate all other existing apps onto the same instance soon in the future.

Why pay the money for 5 (or more) instances if you can get things done in just one intance?