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Reliability block diagram templates

Availability model — payments API across three AZs

Reliability block diagram of a regional payments API — Route 53, ALB, 2-of-3 AZ stacks, Aurora storage with a hot-standby writer and a third-party card processor — solving to 99.938% steady-state availability and naming the ALB and the processor as the two blocks that cap it.

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Payments API — regional availability modelMission 720 h · 30.0 d · 9 blocks · 2 redundant arrangements · R 0.658802Route 53 hosted zoneR 0.991815 · A 0.99999Application Load BalancerR 0.921095 · A 0.999902 of 3 · R 0.808475AZ-a stack (nodes + pods)R 0.719811 · A 0.99989AZ-b stack (nodes + pods)R 0.719811 · A 0.99989AZ-c stack (nodes + pods)R 0.719811 · A 0.99989Aurora cluster volumeR 0.991815 · A 0.99999hot standby · switch 0.995 · R 0.976379Aurora writer instanceR 0.848417 · A 1.00000Aurora reader (promotable)R 0.848417 · A 1.00000Card processor (99.95% SLA)R 0.921095 · A 0.99950System reliability0.658802Unreliability0.3412System MTTF1 256 h · 52.3 dAvailability0.999383Reliability importance — Birnbaum ∂R/∂Rᵢ, with criticality share1Application Load Balancer0.715238crit 17%2Card processor (99.95% SLA)0.715238crit 17%3Route 53 hosted zone0.664240crit 1.59%4Aurora cluster volume0.664240crit 1.59%5AZ-a stack (nodes + pods)0.328692crit 27%6AZ-b stack (nodes + pods)0.328692crit 27%7AZ-c stack (nodes + pods)0.328692crit 27%8Aurora writer instance0.105142crit 4.67%+1 more blocks not shownWeakest link: Application Load Balancer — R 0.921095, Birnbaum 0.715238, 17% of system failure. Improving this one block moves the system number further than improving any other.Redundancy check: removing any one of the 4 branches makes its own group measurably more likely to fail — the least of them by 152%. Every one of them is earning its place.

Make it your own.

title "Payments API — regional availability model"
mission 720h

# A 30-day SLO window. Every block carries an MTBF and an MTTR, so the
# figure reports steady-state availability as well as mission reliability.

block dns      "Route 53 hosted zone"        mtbf: 87600h  mttr: 0.5h
block alb      "Application Load Balancer"   mtbf: 8760h   mttr: 0.88h
block az1      "AZ-a stack (nodes + pods)"   mtbf: 2190h   mttr: 0.25h
block az2      "AZ-b stack (nodes + pods)"   mtbf: 2190h   mttr: 0.25h
block az3      "AZ-c stack (nodes + pods)"   mtbf: 2190h   mttr: 0.25h
block storage  "Aurora cluster volume"       mtbf: 87600h  mttr: 1h
block writer   "Aurora writer instance"      mtbf: 4380h   mttr: 0.0083h
block reader   "Aurora reader (promotable)"  mtbf: 4380h   mttr: 0.0083h
block psp      "Card processor (99.95% SLA)" mtbf: 8760h   mttr: 4.38h

series {
  dns
  alb
  kofn 2 of 3 { az1; az2; az3 }
  storage
  standby hot { primary: writer; spare: reader; switch: 0.995 }
  psp
}