In Docker Swarm, that's a Stack. K8s has no equivalent. So there's no answer to "how do i deploy/update my flask api and celery workers together"
This makes it especially easy for anyone transitioning from Docker Swarm to Kubernetes.
In Swarm, the stack is an atomic unit.
That's what Microsoft is trying to fix - the atomicity of an abstraction level that is higher than K8s Services.
Not sure why they didnt do this as part of the k8s core committee process.
My take is that the equivalent in k8s is it's declarative management with configuration files. Just kubectl apply -f your.yaml and you're good to go.