How do you load test a Go microservice and interpret the results?

// Vegeta: Go-native load testing library
import vegeta "github.com/tsenart/vegeta/v12/lib"

func LoadTestGetUser(t *testing.T) {
    if testing.Short() { t.Skip("skipping load test in short mode") }

    rate    := vegeta.Rate{Freq: 100, Per: time.Second} // 100 RPS
    duration := 30 * time.Second
    targeter := vegeta.NewStaticTargeter(vegeta.Target{
        Method: "GET",
        URL:    "http://localhost:8080/users/1",
    })

    attacker := vegeta.NewAttacker()
    var metrics vegeta.Metrics
    for res := range attacker.Attack(targeter, rate, duration, "load test") {
        metrics.Add(res)
    }
    metrics.Close()

    t.Logf("Requests:  %d", metrics.Requests)
    t.Logf("Success:   %.2f%%", metrics.Success*100)
    t.Logf("Throughput: %.2f rps", metrics.Throughput)
    t.Logf("Latency p50: %v", metrics.Latencies.P50)
    t.Logf("Latency p95: %v", metrics.Latencies.P95)
    t.Logf("Latency p99: %v", metrics.Latencies.P99)

    // Assertions
    if metrics.Success < 0.999 {
        t.Errorf("success rate %.2f%% below 99.9%%", metrics.Success*100)
    }
    if metrics.Latencies.P99 > 50*time.Millisecond {
        t.Errorf("p99 latency %v exceeds 50ms SLO", metrics.Latencies.P99)
    }
}

// Benchmark as a proxy for load test (lower overhead)
func BenchmarkHandlerThroughput(b *testing.B) {
    srv := httptest.NewServer(buildRouter())
    defer srv.Close()
    client := srv.Client()

    b.SetParallelism(10) // 10 goroutines × GOMAXPROCS concurrent
    b.ResetTimer()
    b.RunParallel(func(pb *testing.PB) {
        for pb.Next() {
            resp, _ := client.Get(srv.URL + "/users/1")
            io.Discard.Write(resp.Body)
            resp.Body.Close()
        }
    })
    b.ReportMetric(float64(b.N)/b.Elapsed().Seconds(), "rps")
}