Requirements & Proof · wrap-up
Cheat sheet & self-check
Every command from this section on one page.
Availability math (30-day month)
99.9% → 43.2 min/month downtime | 43,200 min × 0.001 |
99.95% → 21.6 min/month | 43,200 × 0.0005 |
99.99% → 4.32 min/month | 43,200 × 0.0001 |
Serial: A = A1 × A2 | 0.999 × 0.999 ≈ 0.998 |
Parallel (independent): A = 1 − (1 − A1)(1 − A2) | two 99% → 99.99% (only if truly independent) |
The NFR sheet
ID · category · requirement · metric · target · measurement · owner | One measurable row per requirement |
Categories: availability, latency, throughput, scalability, durability (RPO/RTO), security, operability, cost | Cover them all |
Baseline tools
sonobuoy run --mode=certified-conformance | Kubernetes conformance tests |
kube-burner init -c <config> | Control-plane / object churn load |
iperf3 -c <pod-ip> -P 4 -t 30 | Pod-to-pod network throughput |
fio --name=etcd --rw=write --ioengine=sync --fdatasync=1 --bs=2300 --size=22m --directory=/var/lib/etcd-test | fsync latency like etcd's WAL |
k6 run load.js | Application load test |
PoC discipline
Success criteria written before starting | Pass/fail per criterion |
Weighted scoring matrix | Criteria × weight × score per option |
Time-box (e.g. 3–4 weeks) | A PoC is not a pilot |
Stability tests
Soak: realistic load for 48–72 h | Leaks, slow degradation, log/disk growth |
Peak + burst profile (k6 stages) | Behaviour at NFR-03 load |
Kill a node / pod / etcd member under load | Recovery time and error budget spent |
Minor upgrade under load | No failed requests (NFR-07) |
Deliverables
Evidence pack | Method, environment, raw results, graphs, issues found and fixed |
Exec one-pager | Recommendation, confidence, risks, cost, next steps |
Risk register | Risk · likelihood · impact · mitigation · owner |
The chain
Demand = Σ (replicas × requests) at peak (+ daemonsets per node) | What workloads reserve |
Allocatable = capacity − system/kube reserved − eviction threshold | What a node can offer |
Usable per node = allocatable × target utilisation (e.g. 70%) | Room for bin-packing and bursts |
Nodes = ceil(demand ÷ usable per node), for CPU and memory; take the larger | Base count |
Survive losing 1 of R racks: nodes × R ÷ (R − 1) | Failure-domain headroom |
Limits to check
max pods per node (kubelet default 110) | Pod density |
pod CIDR per node (e.g. /24 → 256 addresses) | IPAM (lesson 06) |
Upstream tested limits: 5,000 nodes, 150,000 pods per cluster, 110 pods per node | Far above most designs, but real |
