系統設計

1type Instance = { cores: number; qps: number; pricePerHour: number };
2 
3// Scale up: the smallest machine that carries the load below the target.
4function pickInstance(qps: number, sizes: Instance[], target = 0.7): Instance | null {
5  for (const size of sizes) {
6    if (size.qps * target >= qps) return size;
7  }
8  // Past the biggest machine there is nothing to buy.
9  return null;
10}
11 
12// Scale out: enough small servers for the load, plus one spare.
13function serversNeeded(qps: number, perServerQps: number, target = 0.7): number {
14  return Math.ceil(qps / (perServerQps * target)) + 1;
15}
16 
17// Stateless: the session is looked up in a shared store on every request,
18// so any server can answer and losing one signs nobody out.
19class Handler {
20  constructor(private sessions: Map<string, string>) {}
21 
22  handle(sessionId: string): { status: number; user?: string } {
23    const user = this.sessions.get(sessionId);
24    if (user === undefined) return { status: 401 };
25    return { status: 200, user };
26  }
27}