Uses for Infrastructure as Code

Non-persistence and Templates

Automation works best in an environment designed for non-persistence
- means that any given instance is completely static in terms of processing function
- Data is kept separate from the instance OS/app
  - so instance can be swapped out for an “as new” copy without suffering any configuration problems
when provisioning a new instance,
- automation system may use two types of mastering instructions:
  - Master Image
    - the “gold” copy of a VM or container instance
      - OS, applications, and patches all installed and configured
    - faster than using a template
    - keeping the image up to date can involve more work than updating a template
  - Automated build from a template
    - build instructions (imperative automation) or desired configuration (declarative automation) for an instance
    - Rather than storing a master image,
      - software builds and provisions an instance according to the template instructions or desired configuration

upgrade process can be highly complex
- can have unforeseen impact
upgrade project must be treated as a major change
- should be supported by test and rollback plans
project must identify:
- dependencies between systems
- how they will be impacted by the upgrade
Automation can assist by:
- speeding up deployment of systems into a test network
- performing scripted test suites to check for known or anticipated compatibility issues
- deploy the upgraded systems on the production network

Instances of VMs and containers launched into a cloud environment need to be tracked as inventory
cloud instances are ephemeral
need to be identified by tags
- Rather than fixed asset IDs
- can be assigned in the cloud management system when the instance is launched
imperative to devise and enforce a tagging system that properly identifies ownership and roles for all instances
important to manage instances to avoid sprawl
- where undocumented instances are launched and left unmanaged
- manage by:
  - restricting rights to launch instances
  - configure logging and monitoring to track usage

A dynamic inventory queries the cloud API to return a list of instances and their properties for storage in a database.

A reusable task or module is a block of code that can perform a function in multiple different contexts.

e.g., given different inputs
- same block of code could
  - launch a Windows VM into subnet A
  - launch a Linux VM into subnet B
Rather than separate scripts, develop function libraries that can be reused for multiple tasks