Concepts

What qfence does, and why, for the people who run it. Each page links to the specification and the decision records in the repository for the reasoning behind it.

• Quorum, ownership and generations: how one site, and only one, comes to own a plan.
• The witness and the availability arithmetic: the third voter, and what stays available when things fail.
• Fencing levels and durable proof: what has to be proven before another site is promoted.
• Returning sites, shields and self-fencing: what protects the survivor when the old site comes back.
• Controllers and bindings: how a plan acts on the systems it protects, and from where.
• Application controllers: watching, restarting and switching over the application itself.
• Secrets: where controllers’ credentials live, and who can read them.