Two-man control can be a strong defence, but the overhead is a concern, as discussed previously.
How can two-man control be implemented with minimal overhead?
I would be most interested in a concrete example: an online banking platform. The environment includes a load balancer, web servers, database servers, and a link to the core banking platform (which is out of scope).
To avoid this question being too broad, lets only consider sys-admins - not developers, support agents, etc.
Some people may say this would be more suited to another site like Server Fault. While the question covers how-to do something, it is something that you would only do for infosec reasons, so it fits best here.