If a want to run a large backfill on k8s using the framework defined here https://discourse.prefect.io/t/i-want-to-use-parameter-values-for-backfilling-but-prefe[…]ter-defaults-provided-at-registration-how-to-solve-that/49 - is there a way to batch things up so I am only ever running say 10 jobs at a time?

You can set a flow-level concurrency limit of 10 to configure that

Is that a cloud setting?

yes

Not on the free tier though? Ok well will have to upgrade for this I think! If I never go over the 20k tasks per month it's still free yeah?

Standard tier is also a free tier

How does the tag interface with the agent tag? If my agent has tag ['a'] and I set a limit on tag ['b'] will my flow still get picked up by the agent if I give it tags ['a','b'] and the concurrency limit for ['b'] will be respected?

if you set the concurrency limit on flow label "b" and your agent has the same label "b" assigned when starting the agent, then there is a match and Prefect will deploy only max. 10 runs of this flow to this matching agent

Ok so for every concurrency limit I setup I need to add a new tag to the agent? But the flow itself only needs to have some subset of the ones on the agent?

correct, the agent can have more labels than your flow's run config does

Perfect! Thanks!