Spinnaker vs Terraform

Essentially, use Terraform to set up your infrastructure and use Spinnaker to manage your deployments. You CAN use Terraform to accomplish Spinnaker tasks but it would require a lot of glue-code that is difficult to copy for other tasks. We see a lot of companies attempting to extend Terraform to do Spinnaker’s tasks when they can simply use Spinnaker.

Where Spinnaker Excels Over Terraform:

• AMI Creation
• Deployment strategies out of the box:
• Highlander
• Blue/Green (also called Red/Black)
• Custom
• Canary

Where Terraform Excels Over Spinnaker:

• Non-deployment related resource creation and management
• VPCs
• Route 53 entries
• Subnets
• S3 buckets
• SQS
• SNS
• Etc.
• One time creation of resources
• Large scale modification of resources
• Lambda
• Defining and managing your infrastructure as code

Source:
https://blog.armory.io/comparing-terraform-and-spinnaker/