Push To Registry

This configures Packer to push build metadata to HCP Packer's registry so you can track which image versions exist and promote them through channels like production or staging. The actual setup is a single hcp_packer_registry block in your build with bucket_name, labels, and descriptions. The real value shows up in Terraform where you query by channel name instead of hardcoding AMI IDs, which means your infrastructure code stays stable while images get updated. Authentication needs a service principal with four environment variables. One thing to watch: bucket_name must stay consistent across builds or you'll fragment your registry into multiple buckets accidentally.