So it's a kind of better Docker Swarm? It's interesting, but honestly I'd rather have something declarative, so I can use it with Pulumi, would it be complicated to add a declarative engine on top of the tool? Which discovers what services are already up, do a diff with the new declaration, and handles changes?

This is exactly how it works now. The Compose file is the declarative specification of your services you want to run.

When you run 'uc deploy' command:

- it reads the spec from your compose.yaml

- inspects the current state of the services in the cluster

- computes the diff and deployment plan to reconcile it

- executes the plan after the confirmation

Please see the docs and demo: https://uncloud.run/docs/guides/deployments/deploy-app

The main difference with Docker Swarm is that the reconciliation process is run on your local/CI machine as part of the 'uc deploy' CLI command execution, not on the control plane nodes in the cluster.

And it's not running in the loop automatically. If the command fails, you get an instant feedback with the errors you can address or rerun the command again.

It should be pretty straightforward to wrap the CLI logic in a Terraform or Pulumi provider. The design principals are very similar and it's written in Go.