《游戏服务端架构·品类、状态与拓扑》1.3 品类如何决定拓扑：北辰三款产品

// file: internal/topology/choose.go
// tier: L1
// verify: go test ./internal/topology/
package topology

// Kind is a first-pass server topology for one product.
type Kind string

const (
	ModularMonolith Kind = "modular-monolith"
	LobbyRoom       Kind = "lobby-room"
	ShardedWorld    Kind = "sharded-world"
	GlobalShard     Kind = "global-single-shard"
	DedicatedPool   Kind = "dedicated-server-pool"
)

// Profile is the handful of product facts that actually change topology.
type Profile struct {
	Name              string
	ConcurrentPlayers int
	SessionMinutes    int
	RealTime          bool // frame or operation budget is player-visible
	SharedWorld       bool // players share one persistent world
	MatchBased        bool // play happens in discrete matches
	RegionSensitive   bool // cross-region latency changes fairness
}

type Decision struct {
	Kind    Kind
	Reasons []string
}

// Choose is a decision aid, not an architecture review. It makes the first
// fork explicit; the ADR still has to justify the cost.
func Choose(p Profile) Decision {
	switch {
	case p.MatchBased && p.RealTime:
		return Decision{
			Kind: LobbyRoom,
			Reasons: []string{
				"matches need isolated failure domains",
				"the lobby can scale statelessly",
			},
		}
	case p.SharedWorld && p.ConcurrentPlayers > 10000:
		return Decision{
			Kind: GlobalShard,
			Reasons: []string{
				"one persistent world with a large population",
				"region routing must be decided before sharding",
			},
		}
	case p.SharedWorld:
		return Decision{
			Kind: ShardedWorld,
			Reasons: []string{
				"persistent world, but population fits a small number of shards",
				"shard by map region or server group first",
			},
		}
	case p.RealTime:
		return Decision{
			Kind: DedicatedPool,
			Reasons: []string{
				"real-time sessions need dedicated capacity",
				"no shared world means instances can be recycled",
			},
		}
	default:
		return Decision{
			Kind: ModularMonolith,
			Reasons: []string{
				"no player-visible real-time pressure",
				"start with one deployable and split only when the boundary hurts",
			},
		}
	}
}

// file: internal/topology/choose_test.go
// tier: L1
// verify: go test ./internal/topology/
package topology

import "testing"

func TestNorthstarProducts(t *testing.T) {
	cases := []struct {
		name string
		p    Profile
		want Kind
	}{
		{
			name: "裂隙战场",
			p: Profile{
				Name: "裂隙战场", ConcurrentPlayers: 200000,
				SessionMinutes: 25, RealTime: true, MatchBased: true, RegionSensitive: true,
			},
			want: LobbyRoom,
		},
		{
			name: "群岛纪元",
			p: Profile{
				Name: "群岛纪元", ConcurrentPlayers: 80000,
				SessionMinutes: 60, SharedWorld: true, RegionSensitive: true,
			},
			want: GlobalShard,
		},
		{
			name: "泡泡工坊",
			p: Profile{
				Name: "泡泡工坊", ConcurrentPlayers: 30000,
				SessionMinutes: 8, MatchBased: true,
			},
			want: ModularMonolith,
		},
	}
	for _, c := range cases {
		got := Choose(c.p)
		if got.Kind != c.want {
			t.Fatalf("%s: got %s, want %s", c.name, got.Kind, c.want)
		}
		if len(got.Reasons) == 0 {
			t.Fatalf("%s: decision has no reasons", c.name)
		}
	}
}

func TestSharedWorldBelowThreshold(t *testing.T) {
	got := Choose(Profile{SharedWorld: true, ConcurrentPlayers: 5000})
	if got.Kind != ShardedWorld {
		t.Fatalf("got %s, want %s", got.Kind, ShardedWorld)
	}
}

$ cd .local/checks/gsarch-lab
$ go test ./internal/topology/ -v
=== RUN   TestNorthstarProducts
--- PASS: TestNorthstarProducts (0.00s)
=== RUN   TestSharedWorldBelowThreshold
--- PASS: TestSharedWorldBelowThreshold (0.00s)
PASS
ok  	gsarchlab/internal/topology	0.4s

立项期：模块化单体，先验证玩法
    │
    ├── 玩法成立、在线增长 → 拆大厅与房间
    │
    ├── 全球化发行 → 加地域路由与分片
    │
    └── 多产品复用 → 平台服务化