The first step toward a HIL lab is getting the target device off your laptop.
Instead of a developer machine plugged directly into a board over USB, you move to a small management node that controls power to the target and talks to it over a fixed set of cables.
Power tends to be the first thing you have to figure out.
Why USB Is Not Enough
USB is convenient, but it isn't always a clean way to control power. Boards can be backpowered through USB itself, through a UART adapter, through a debug probe, or through any other line that happens to be connected.
Cheap USB on/off hubs don't always fully remove power either. The current limits on a USB port can be fine for many MCU boards, but they fall short for embedded Linux boards or custom prototypes that draw more.
PoE can be a clean option when it fits, but it adds cost, and not every board has an Ethernet port.
Two Practical Starting Points
Relays are simple and cheap. A 4 or 8 port relay board is plenty for early prototypes. Tie the relay control side to GPIOs on the management node and switch the DUT supply rail from software. Pull the GPIO high, the relay closes, the DUT gets power. Pull it low, the DUT goes dark. That's a hard reset you can trust.
The relay should switch the positive supply rail. Keep ground connected.
Relays give you on/off control and not much else. There is no protection, no current monitoring, and no insight into what the DUT is doing on the power side.
Protected power channels are more involved, usually PCB-based, and they let you add current limits, current monitoring, fault handling, and safer per-device control.
Our first prototype was relay-based. We then moved to a PCB with protected power channels, and even that first PCB did not last long. It had obvious mistakes, and it quickly became clear we wanted an MCU on the power board to handle smarter control.
Respinning a PCB a few times is part of the process. The relay version is still worth building, because it tells you what your test flow really needs before you've committed to anything that's harder to change.