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loadshed

LoadShed

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The LoadShed middleware for Fiber is designed to help manage server load by shedding requests based on certain load criteria.

Note: Requires Go 1.19 and above

Install

This middleware supports Fiber v2

go get -u github.com/gofiber/fiber/v2
go get -u github.com/gofiber/contrib/loadshed

Signatures

loadshed.New(config ...loadshed.Config) fiber.Handler

Examples

To use the LoadShed middleware in your Fiber application, import it and apply it to your Fiber app. Here's an example:

package main

import (
  "github.com/gofiber/fiber/v2"
  loadshed "github.com/gofiber/contrib/loadshed"
)

func main() {
  app := fiber.New()

  // Configure and use LoadShed middleware
  app.Use(loadshed.New(loadshed.Config{
    Criteria: &loadshed.CPULoadCriteria{
      LowerThreshold: 0.75, // Set your own lower threshold
      UpperThreshold: 0.90, // Set your own upper threshold
      Interval:       10 * time.Second,
      Getter:         &loadshed.DefaultCPUPercentGetter{},
    },
  }))

  app.Get("/", func(c *fiber.Ctx) error {
    return c.SendString("Welcome!")
  })

  app.Listen(":3000")
}

Config

The LoadShed middleware in Fiber offers various configuration options to tailor the load shedding behavior according to the needs of your application.

Property Type Description Default
Next func(*fiber.Ctx) bool Function to skip this middleware when returned true. nil
Criteria LoadCriteria Interface for defining load shedding criteria. &CPULoadCriteria{...}

LoadCriteria

LoadCriteria is an interface in the LoadShed middleware that defines the criteria for determining when to shed load in the system. Different implementations of this interface can use various metrics and algorithms to decide when and how to shed incoming requests to maintain system performance.

CPULoadCriteria

CPULoadCriteria is an implementation of the LoadCriteria interface, using CPU load as the metric for determining whether to shed requests.

Properties

Property Type Description
LowerThreshold float64 The lower CPU usage threshold as a fraction (0.0 to 1.0). Requests are considered for shedding when CPU usage exceeds this threshold.
UpperThreshold float64 The upper CPU usage threshold as a fraction (0.0 to 1.0). All requests are shed when CPU usage exceeds this threshold.
Interval time.Duration The time interval over which the CPU usage is averaged for decision making.
Getter CPUPercentGetter Interface to retrieve CPU usage percentages.

How It Works

CPULoadCriteria determines the load on the system based on CPU usage and decides whether to shed incoming requests. It operates on the following principles:

  • CPU Usage Measurement: It measures the CPU usage over a specified interval.
  • Thresholds: Utilizes LowerThreshold and UpperThreshold values to decide when to start shedding requests.
  • Proportional Rejection Probability:
    • Below LowerThreshold: No requests are rejected, as the system is considered under acceptable load.
    • Between LowerThreshold and UpperThreshold: The probability of rejecting a request increases as the CPU usage approaches the UpperThreshold. This is calculated using the formula: 
      rejectionProbability := (cpuUsage - LowerThreshold*100) / (UpperThreshold - LowerThreshold)
    • Above UpperThreshold: All requests are rejected to prevent system overload.

This mechanism ensures that the system can adaptively manage its load, maintaining stability and performance under varying traffic conditions.

Default Config

This is the default configuration for LoadCriteria in the LoadShed middleware.

var ConfigDefault = Config{
  Next: nil,
  Criteria: &CPULoadCriteria{
    LowerThreshold: 0.90,  // 90% CPU usage as the start point for considering shedding
    UpperThreshold: 0.95,  // 95% CPU usage as the point where all requests are shed
    Interval:       10 * time.Second,  // CPU usage is averaged over 10 seconds
    Getter:         &DefaultCPUPercentGetter{},  // Default method for getting CPU usage
  },
}