Six Links In Series

Every user request touches six internal services in sequence, and a failure in any one fails the request. Each service independently meets 99.9 percent availability. Your team's own SLO is 99.9 percent monthly, over a 30 day month.

What is the composed availability of the chain, and what does that mean for your budget?

About 99.9999 percent, because six independent services are unlikely to fail at the same moment

About 99.40 percent, and the chain alone burns roughly 259 minutes a month, about six times the 43 minute budget a 99.9 percent SLO allows

About 99.90 percent, because a chain is only as available as its least available link, so the budget is exactly consumed and nothing is left over

About 99.40 percent, and the chain burns roughly 43 minutes, exactly the budget, leaving no room for your own defects