Comparison of Infrastructure as Code tools

Source - Multiple articles by Yevgeniy Brikman & other online articles:

	Source	Cloud	Type	Infrastructure	Language	Agent	Master	Community	Maturity	Initial Release
Chef	Open	All	Config Mgmt	Mutable	Procedural	Yes	Yes	Large	High	2005
Puppet	Open	All	Config Mgmt	Mutable	Declarative	Yes	Yes	Large	High	2009
Ansible	Open	All	Config Mgmt	Mutable	Procedural	No	No	Large	Medium	2011
SaltStack	Open	All	Config Mgmt	Mutable	Declarative	Yes	Yes	Medium	Medium	2011
CloudFormation	Closed	AWS	Provisioning	Immutable	Declarative	No	No	Small	Medium	2012
Heat	Open	All	Provisioning	Immutable	Declarative	No	No	Small	Low	2012
Terraform	Open	All	Provisioning	Immutable	Declarative	No	No	Medium	Low	2014
Deployment Manager		GCP	Config Mgmt		Declarative					2015
Pulumi	Open	All	Provisioning	Immutable	Declarative					2017

The goal of DevOps is to make software delivery vastly more efficient.

Instead of constant outages and downtime, you build resilient, self-healing systems, and use monitoring and alerting to catch problems that can’t be resolved automatically.

There are four core values in the DevOps movement: Culture, Automation, Measurement, and Sharing (sometimes abbreviated as the acronym CAMS)

The idea behind infrastructure as code (IAC) is that you write and execute code to define, deploy, and update your infrastructure.

There are four broad categories of IAC tools:
- Ad hoc scripts
- Configuration management tools
- Server templating tools
- Server provisioning tools

Chef, Puppet, Ansible, and SaltStack are all configuration management tools, which means they are designed to install and manage software on existing servers.

Code that works correctly no matter how many times you run it is called idempotent code.

An alternative to configuration management that has been growing in popularity recently are server templating tools such as Docker, Packer, and Vagrant.

A server templating tool like Packer can be used to create a self-contained image of a server. You can then use other tools, such as Ansible, to install that image across all of your servers.

A virtual machine (VM) emulates an entire computer system, including the hardware. You run a hypervisor, such as VMWare, VirtualBox, or Parallels, to virtualize (i.e., simulate) the underlying CPU, memory, hard drive, and networking.

A container emulates the user space of an operating system. All the containers running on a single server share that server’s operating system kernel and hardware, so the isolation is not as secure as with VMs.

VMs virtualize the hardware, whereas containers only virtualize user space.

Server templating is a key component of the shift to immutable infrastructure. The idea behind immutable infrastructure is that once you’ve deployed a server, you never make changes to it again. If you need to update something (e.g., deploy a new version of your code), you create a new image from your server template and you deploy it on a new server.

Server provisioning tools such as Terraform, CloudFormation, and OpenStack Heat are responsible for creating the servers themselves.

When it comes to IaC tools, some rely on a domain-specific language (DSL), while others use a standard template format, such as YAML and JSON.

A declarative style is great when you need to update your infrastructure or make any changes to it. Whereas the imperative is good for a deploy and forget model, but that isn’t always great if you’re looking to be an agile organization or have a changing infrastructure. 

Terraform is a binary that translates the contents of your configurations into API calls to cloud providers

GCP Deployment Manager is a hosted service that allows you to integrate with other GCP services such as Identity Access Management like Cloud Formation from AWS which is only structured to work within AWS infrastructure, and it integrates well with AWS services.

Terraform is the swiss army knife of IaC tools. It is not only idempotent, Terraform is completely cloud-agnostic and helps you tackle large infrastructure for complex distributed applications.  

Ansible provides a “radically simple” IT automation engine. It is designed for multi-tier deployments and uses no agents. Ansible is a strong fit for configuration management, application deployment, and intra-service orchestration by describing how all the systems inter-relate.

Also see - 

Infrastructure as Code (IaC): Comparing the Tools (2022)

Configuration Management, Configuration Orchestration

Pulumi vs. Terraform