Terraform

Terraform Open external link is a tool for building, changing, and versioning infrastructure, and provides components and documentation for building Open Ecosystems resources.

Terraform is HashiCorp’s Infrastructure as Code. It allows one to describe a Desired State. By deploying it Terraform will make the necessary changes to make sure that the Current State matches the Desired State.

​​ Desired State

With Terraform the Desired State is described using HCL¹.

Former2 Open external link is a great tool to create such a file from an existing infrastructure.

​​ State File

Terraform makes use of a State File. Whenever it deployed a Desired State, it will save it in the State File. If the Desired State is (changed and) deployed Terraform will not actually compare the Desired State to the Current State, but to the State File.

​​ Advantages

Having a State File has some advantages:

• It is much easier to compare the Desired State to a local file (the State File, than it is to the real Current State, because the latter will involve a lot of API calls to the IaaS or DCaaS layer.
• The State File can also be parsed by other tools, which gives them an easy to read model of what the infrastructure currently looks like.

​​ Disadvantages

Having a State File also has some disadvantages:

• The State File must be stored on Shared Storage, and it can never get lost, or it would break Infrastructure as Code. These requirements are not easily met.
• Nothing and nobody else can make changes to the infrastructure outside of Terraform. If changes are made, they will NOT be detected by Terraform, which results in an infrastructure that does NOT match the Desired State, although everything seems to be saying it is.