Blue and green share a container; the alias picks the port

Release 41 listens on 3000. You start release 42 on 3001 in the same container, hit it on its own cryptographic http-3001 URL, and watch it for an hour.

The public alias points at program: http, port: 3000. Cutover is PATCH /api/v1/proxy/aliases/{id} with {"port": 3001}. Rollback is the same request with 3000. The container is fixed when the alias is created and can't change; the port can, any time, and the CNAME from api.acme.com never learns anything happened.

No second container to warm, no load balancer to reconfigure, no DNS TTL to wait out. Both releases keep running until you stop the old one, so rollback is a field change, not a redeploy.

The deploy is one field on the alias, and the field is a port number.