factories

The why and the how of Resource Factories

Terraform modules can be designed - where it makes sense - to implement a resource factory, which is a configuration-driven approach to resource creation meant to:

• accelerate and rationalize the repetitive creation of common resources, such as firewall rules and subnets
• enable teams without Terraform specific knowledge to leverage IaC via human-friendly and machine-parseable YAML files
• make it simple to implement specific requirements and best practices (e.g. "always enable PGA for GCP subnets", or "only allow using regions europe-west1 and europe-west3")
• codify and centralise business logics and policies (e.g. labels and naming conventions)
• allow to easily parse and understand sets of specific resources, for documentation purposes

Generally speaking, the configurations for a resource factory consists in one or more YaML files, optionally grouped in folders, that describe resources following a well defined, validable schema, such as in the example below for the subnet factory of the net-vpc module, which allows for the massive creation of subnets for a given VPC.

region: europe-west3
ip_cidr_range: 10.0.0.0/24
description: Sample Subnet in project project-prod-a, vpc-alpha
secondary_ip_ranges:
  secondary-range-a: 192.168.0.0/24
  secondary-range-b: 192.168.1.0/24

Terraform natively supports YaML, JSON and CSV parsing - however Fabric has decided to embrace YaML for the following reasons:

• YaML is easier to parse for a human, and allows for comments and nested, complex structures
• JSON and CSV can't include comments, which can be used to document configurations, but are often useful to bridge from other systems in automated pipelines
• JSON is more verbose (reads: longer) and harder to parse visually for humans
• CSV isn't often expressive enough (e.g. dit doesn't allow for nested structures)

If needed, converting factories to consume JSON is a matter of switching from yamldecode() to jsondecode() in the right place on each module.

Resource factories in Fabric

Fabric Modules

• folder and organization implement factories for hierarchical firewall policies
• net-vpc for subnets creation
• net-vpc-firewall for massive rules creation

Dedicated Factories

• cloud-identity-group-factory for Cloud Identity group
• net-vpc-firewall-yaml for VPC firewall rules across different projects/VPCs
• project-factory for projects