Introduction to 67 Bricks immutable deployments

Since the rise of cloud computing, the way of creating and maintaining infrastructure has changed. While some years ago an unhealthy machine needed to be logged in and fixed manually, or even worse, turned off and a new one had to be configured from scratch by a systems administrator, thanks to modern technologies it has become possible to not worry about whether a resource is configured in exactly the same way.

This post summarizes the main tools used at 67 Bricks for deployment of the services that we host and manage, and describes our deployment process.

A dictionary definition of immutability is “the state of not changing, or being unable to be changed”. And this is what deploying immutably is about – after being released, infrastructure does not change in place, and in order to make changes, a new version is provisioned and the old version is destroyed.

Some of the benefits of immutability include the following:

  1. Consistency of environments – the same processes and procedures are applied to create environments for staging, testing and live, thereby making it easier to test.
  2. An immutable deployment pipeline means that what happens during deployments is documented by using configuration as code – this enables developers to understand the services better and know exactly what happens at each stage.
  3. Having configuration stored as code in a repository facilitates spinning up new services thus improving speed of development.
  4. The ability to reproduce resources aids immensely in automated disaster recovery where it might only take a few minutes to replace an unhealthy resource with a new one.
  5. Immutable deployments allow dynamic scaling of resource in the cloud based on demand.

Tool Used

  • We use Gitlab as our internal code repository, and CI/CD system.

At 67 Bricks we use a variety of modern tools and technologies to deploy our services.

  • Packer is used to create a server image with the software baked onto it.
  • AWS is typically where we deploy applications.
  • Ansible is used to configure servers, called by Packer during the image build phase.
  • Terraform is used to provision infrastructure.

Deployment process

Firstly, an environment or multiple environments are created in an AWS account using Terraform, and resources such as VPC (virtual private cloud) are launched.

Secondly, a base image is built daily off one of AWS AMIs (Amazon Machine Images). By means of Ansible, latest packages are fetched and tools such as AWS CLI and snap updates are installed, as well as automatic security updates are configured. This image is available to developers to use for their application. Since a lot of our applications run on Linux, we use Ubuntu to build the base image

When code is merged into the main/master branch in Gitlab, this starts a pipeline during which the application is built, tests are run and an AMI with the application installed is created via Packer, with Ansible tasks configuring the machine for the use by a specific application. This image is tagged so that we know which application is on it.

After that, the pipeline deploys the application to test and then to live. We use autoscaling for our applications (specifically, AWS AutoScaling Groups), and to use the newly built image with the new version of the application, a script is used to destroy existing application servers and create new ones with the updated version of the application installed. Autoscaling Group configuration is also amended to use the new AMI for any autoscaling events.

When servers (or EC2 instances, in AWS speak) are launched in an autoscaling group, a user_init script gets run on initialization. This is the stage at which any environment specific setup can be done.

Immutability is of paramount importance if you want to create a simpler, more predictable deployment pipeline whose outcome is trusted. Our teams have adopted the immutable deployment approach, and it helps us to ensure repeatable processes and reliable services and applications are in place.

Author: Oksana Horlock

I've been at 67 Bricks for 1.5 years. I started as a Software Developer and then took on the position of Site Reliability Engineer. Some of my interests are AWS, Infrastructure as Code and diversity in tech. In my free time I like to learn languages and practise salsa, bachata and kizomba.