Load Shedding

Load Shedding

go-zero uses an adaptive load shedder based on CPU utilisation and in-flight request count. When the system is overloaded, new requests are rejected with HTTP 503 / gRPC UNAVAILABLE to protect existing in-flight work.

How It Works

The shedder measures:

• CPU usage — if above threshold (default 90%), shedding activates
• Pass rate — the ratio of accepted to total requests in a window

Requests are shed probabilistically, allowing a controlled fraction through while the system recovers.

HTTP Service

Load shedding is enabled by default. To configure the CPU threshold:

etc/app.yaml

CpuThreshold: 900  # 90.0% — millicores * 10

Disable shedding (not recommended for production):

server := rest.MustNewServer(c.RestConf, rest.WithNotAllowedHandler(...))

gRPC Service

The SheddingInterceptor is registered automatically on every zrpc server.

Custom Shedder

import "github.com/zeromicro/go-zero/core/load"

shedder := load.NewAdaptiveShedder(
    load.WithCpuThreshold(800),  // 80%
)

promise, err := shedder.Allow()
if err != nil {
    // shed this request
    return nil, status.Error(codes.ResourceExhausted, "overloaded")
}
defer func() {
    if err != nil {
        promise.Fail()
    } else {
        promise.Pass()
    }
}()