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Reliability block diagram templates

RBD — Dual-Carrier WAN Path

One-month SLA window on a payments WAN path: two independent edge-router-plus-carrier legs with an LTE bearer, a firewall cluster, core fabric and anycast DNS.

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Dual-carrier WAN path to the payments coreMission 720 h · 30.0 d · 9 blocks · 2 redundant arrangements · R 0.984331parallel · R 0.986176Edge router AR 0.996406 · A 0.99999Carrier A MPLS circuitR 0.835270 · A 0.99900Edge router BR 0.996406 · A 0.99999Carrier B DIA circuitR 0.786628 · A 0.99800LTE failover bearerR 0.618783 · A 0.99933parallel · R 0.999977Firewall cluster node AR 0.995212 · A 0.99999Firewall cluster node BR 0.995212 · A 0.99999Core switch fabricR 0.998202 · A 1.00000Anycast DNS resolverR 0.999950System reliability0.984331Unreliability0.0157System MTTF5 343 h · 223 dAvailability0.999995Reliability importance — Birnbaum ∂R/∂Rᵢ, with criticality share1Core switch fabric0.986104crit 11%2Anycast DNS resolver0.984380crit 0.31%3Carrier A MPLS circuit0.081969crit 86%4Edge router A0.068713crit 1.58%5Carrier B DIA circuit0.063593crit 87%6Edge router B0.050204crit 1.15%7LTE failover bearer0.036195crit 88%8Firewall cluster node A0.004714crit 0.14%+1 more blocks not shownThe availability figure of 0.999995 is computed over 8 of the 9 blocks in this arrangement. The other 1 state no `mttr:` and are fed in at availability 1 — perfectly available, for ever…Weakest link: Core switch fabric — R 0.998202, Birnbaum 0.986104, 11% of system failure. Improving this one block moves the system number further than improving any other.Redundancy check: removing any one of the 5 branches makes its own group measurably more likely to fail — the least of them by 162%. Every one of them is earning its place.

Make it your own.

title "Dual-carrier WAN path to the payments core"
mission 720h                 # one month, matching the SLA window

block edgeA    "Edge router A"           mtbf: 200000h mttr: 2h
block edgeB    "Edge router B"           mtbf: 200000h mttr: 2h
block carrierA "Carrier A MPLS circuit"  mtbf: 4000h   mttr: 4h
block carrierB "Carrier B DIA circuit"   mtbf: 3000h   mttr: 6h
block lte      "LTE failover bearer"     mtbf: 1500h   mttr: 1h
block fwA      "Firewall cluster node A" mtbf: 150000h mttr: 1h
block fwB      "Firewall cluster node B" mtbf: 150000h mttr: 1h
block core     "Core switch fabric"      mtbf: 400000h mttr: 2h
block dns      "Anycast DNS resolver"    r: 0.99995

# Each leg is router + circuit in series; the legs and the LTE bearer are
# the redundancy. Circuits, not routers, are what actually break.
series {
  parallel {
    series { edgeA; carrierA }
    series { edgeB; carrierB }
    lte
  }
  parallel { fwA; fwB }
  core
  dns
}