A check in gate is the only approved way in to airports but the concept extends to the heavily defended entrances of castles and now maybe we should do the same with managing changes to data centres...?
For any data centre, the best place for a control gate could be a source control system (hence the "check in").
With this "source control enabled" deployment solution, if you can't check in the fully automated change, you can't apply it to the IT environment.
The defence or quality on the "change gate" is the automation that enables workflow, testing and ultimately, fully controlled production changes. For more on this see my post continuous deployment.
With better control comes better security - just like a castle!