A regional delivery app is having its best week ever — real growth, not a viral spike, and it needs a front door to fan traffic across a small fleet. It's nowhere near the scale that justifies the premium managed load balancer your last job always reached for. Match the front door to the traffic you actually have.
Requirements
Functional
·Front door fans traffic out across a small fleet of app servers
Non-functional
·~2,400 requests/sec
·95% reads
·p99 latency ≤ 200ms
·99% availability
Constraints
·Budget: $22/hr or less
·Traffic is well under either front-door option's ceiling — this is a price/performance decision, not a capacity one
Out of scope
·Multi-region routing
·Geo-based traffic steering
TrafficRequests per second — the rate of incoming traffic this level throws at your system.
~2400 r/s · read-heavy
95% reads · 5% writesWhat fraction of requests are reads (fetches) vs writes (updates) — this decides which components sit on the hot path.
Win conditions
p99 latency99% of requests finish at or under this time — a stricter tail-latency bar than p95 that catches worst-case slowness.≤ 200ms
availabilityThe share of legitimate requests that succeeded, out of everything sent your way. 99% still means 1 in 100 users saw an error.≥ 99%
throughputHow many requests per second your system actually completed — not requested, completed.≥ 2200 r/s
error rateThe share of requests that failed outright: timeouts, drops, or capacity overload.≤ 2%
costWhat your architecture costs to run per hour, based on the instances and components you've wired up.≤ $22/hr
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Components
Client
ClientWhere traffic originates.
Compute
API GatewayFront door — the app tier requests pass through.
500 r/s · 20ms · $2/hr
BackendA second compute tier for heavier processing.
350 r/s · 25ms · $2/hr
Storage
SQL DatabaseRelational store. Durable, but the lowest throughput.
200 r/s · 50ms · $3/hr
NoSQL DB3× the throughput of SQL — at a premium. Pay for it only when the load demands it.
600 r/s · 30ms · $4/hr
Redis CacheIn-memory read-cache — absorbs repeated reads. Useless for writes.
5000 r/s · 3ms · $2/hr
Read Replica
200 r/s · 55ms · $3/hr
Lvl 12
DB Standby
200 r/s · 50ms · $3/hr
Lvl 13
Networking
CDNEdge read-cache — serves content near the user.
50000 r/s · 5ms · $1/hr
Load BalancerManaged, premium front door — highest ceiling, lowest latency, costs more.
10000 r/s · 2ms · $2/hr
Reverse ProxyCheaper self-hosted front door — lower ceiling, the smart buy under 8,000 r/s.
8000 r/s · 3ms · $1/hr
Messaging
QueueACKs writes instantly, drains them to storage — absorbs bursts, not sustained overload.