Infrastructure as Code Concepts
External
Internal
Overview
Infrastructure is not something you build and forget, in requires constant change: fixing, updating and improving. Infrastructure as Code is a set of technology and engineering practices aimed at delivering change more frequently (or, some would say continuously), quickly and reliably, while improving the overall quality of the system at the same time. Trading speed for quality is a false dichotomy. Used correctly, Infrastructure as Code embeds speed, quality, reliability and compliance into the process of making changes. Changing infrastructure becomes safer. Infrastructure as Code is based on practices from software development, especially test driven development, continuous integration and continuous delivery.
The capability to make changes frequently and reliably is correlated with organizational success. Organizations can't choose between being good at change or being good at stability. They tend to either be good at both or bad at both. (Accelerate by Dr. Nicole Forsgren, Jez Humble and Gene Kim). Changes include adding new services, such as a new database, upgrades, increase of resources to keep up with load, change and tune underlying application runtimes for diagnosis and performance reasons, security patches. Stability comes from the capability of making changes fast and easy: unpatched systems are not stable, they are vulnerable. If you can't fix issues as soon as you discover them, the system is not stable. If you can't recovery from failure quickly, the system is not stable. If the changes you make involve considerable downtime, the system is not stable. If changes frequently fail, the system is not stable. Infrastructure as Code practices help teams perform well against the operational metrics described here.
Automating an existing system is hard. Automation, including automated testing and delivery, should be part of the system's design and implementation, it should evolve organically with the system. You should build the system incrementally, automating as you go.
Core Practices
Define Everything as Code
Code can be versioned and compared, it can benefit from lessons learned in software design patterns, principles and techniques such as test driven development, continuous integration, continuous delivery or refactoring.
Once a piece of infrastructure has been defined as code, many identically or slightly different instances of it can be created automatically by tools, automatically tested and deployed. Instances built by tools are built the same way every time, which makes the behavior of the system predictable. Moreover, everyone can see how the infrastructure has been defined by reviewing the code. Structure and configuration can be automatically audited for compliance.
If more people work on the same piece of infrastructure, the changes can be continuously integrated and continuously tested, as described below.
Continuously Test and Deliver
Continuously test and deliver all work in progress. Continuously testing small pieces encourages a modular, loosely coupled design. It also helps you find problems sooner, then quickly iterate, fix and rebuild the problematic code, which yields better infrastructure.
Build Small, Simple, Loosely Coupled Pieces that Can Be Changed Independently
Microservices fall into this category.
Stack
Collection of infrastructure resources provisioned from cloud platforms.