So, exactly who should attend a postmortem?

First off, who should be on the invite list? With few exceptions (e.g to protect sensitive information or somebody’s personal privacy), make it an open session, available to everyone who wants to attend. At the very least, you’re going to want to make sure that the meeting notes and action items are shared openly. It’s especially important that the key stakeholders attend; people that introduced the defect, and those that identified and fixed it.

Secondly, you’re going to want to have a facilitator present to call out bias. The facilitator keeps the discussion productive and fair. The facilitator is going to keep things on the rails with the mindset that these are complex systems and we have an imperfect understanding of dependencies, so how do we make our changes safer and provide more information next time?