balancer.go

package balancer

import (
	"errors"
)

var (
	NoHostError                = errors.New("no host")
	AlgorithmNotSupportedError = errors.New("algorithm not supported")
)

// Balancer interface is the load balancer for the reverse proxy
type Balancer interface {
	Add(string, int)
	Remove(string)
	Balance(string) (string, error)
	Inc(string)
	Done(string)
}

// Factory is the factory that generates Balancer,
// and the factory design pattern is used here
type Factory func([]string, []int) Balancer

var factories = make(map[string]Factory)

// Build generates the corresponding Balancer according to the algorithm
func Build(algorithm string, hosts []string, hostsWeights []int) (Balancer, error) {
	if len(hosts) == 0 {
		return nil, NoHostError
	}
	balancerBuilder, ok := factories[algorithm]
	if !ok {
		return nil, AlgorithmNotSupportedError
	}
	return balancerBuilder(hosts, hostsWeights), nil
}