Golang learning Web server load balancing

With the increasing number of Internet application scenarios, the issue of load balancing on the Web server has received more and more attention. Especially for sites with high traffic and high concurrency, load balancing can significantly improve system performance and stability. This article will introduce how to use Golang to implement load balancing on the web server.

1. The basic concept of load balancing

The so-called load balancing refers to allocating a certain number of requests to multiple servers for processing, thereby improving the performance and availability of the entire system. The core of load balancing is the scheduling algorithm. Common scheduling algorithms include polling, weighted polling, hash algorithm, etc. The specific scheduling algorithm selected depends on the specific application scenario and business requirements.

2. Use Golang to achieve load balancing

As an efficient programming language, Golang also provides good support for load balancing on the Web server. Golang's standard library provides the net/http package, which we can use to implement load balancing on the Web server.

1. Define an HTTP reverse proxy

First, we need to define an HTTP reverse proxy. HTTP reverse proxy refers to forwarding client requests to multiple servers and returning the response results to the client. The code is as follows:

type Proxy struct {
    urls []*url.URL
    mu   sync.Mutex
}
 
func (p *Proxy) addUrl(addr string) error {
    u, err := url.Parse(addr)
    if err != nil {
        return err
    }
    p.mu.Lock()
    p.urls = append(p.urls, u)
    p.mu.Unlock()
    return nil
}
 
func (p *Proxy) ServeHTTP(w http.ResponseWriter, r *http.Request) {
    p.mu.Lock()
    defer p.mu.Unlock()
    if len(p.urls) == 0 {
        http.Error(w, "No upstream server", http.StatusServiceUnavailable)
        return
    }
    u := p.urls[rand.Intn(len(p.urls))]
    proxy := httputil.NewSingleHostReverseProxy(u)
    proxy.ServeHTTP(w, r)
}

In the above code, we first define a structure Proxy, which contains a pointer slice urls pointing to multiple URLs and a mutex mu. In the addUrl method, we can add multiple URLs to urls. In the ServeHTTP method, we use a mutex lock to first determine whether there are available URLs in urls. If not, we will return an HTTP 503 status code indicating that the service is unavailable. Otherwise, we randomly pick a URL from urls and create a reverse proxy instance using httputil.NewSingleHostReverseProxy. Finally, we call the proxy.ServeHTTP method to forward the request to the corresponding server for processing.

2. Use scheduling algorithms to achieve load balancing

We can use scheduling algorithms such as polling, weighted polling, and hash algorithms to achieve load balancing. The following takes the weighted polling algorithm as an example to introduce.

type WeightedNode struct {
    URL         string
    Weight      int
    Current     int
}
 
type WeightedRoundRobinBalancer struct {
    nodes   []*WeightedNode
    total   int
    current int
    mu      sync.Mutex
}
 
func (b *WeightedRoundRobinBalancer) nextNode() *WeightedNode {
    if b.total == 0 {
        return nil
    }
    for i := 0; i < b.total; i++ {
        node := b.nodes[b.current]
        node.Current = node.Current + node.Weight
        b.current = (b.current + 1) % b.total
        if node.Current >= b.total {
            node.Current = node.Current - b.total
            return node
        }
    }
    return nil
}
 
func (b *WeightedRoundRobinBalancer) ServeHTTP(w http.ResponseWriter, r *http.Request) {
    b.mu.Lock()
    node := b.nextNode()
    b.mu.Unlock()
    if node == nil {
        http.Error(w, "No upstream server", http.StatusServiceUnavailable)
        return
    }
    proxy := httputil.NewSingleHostReverseProxy(node.URL)
    proxy.ServeHTTP(w, r)
}

In the above code, we first define a weighted round robin scheduling algorithm structure WeightedRoundRobinBalancer. The structure contains a pointer slice nodes that points to multiple weighted nodes, the total weight total, the current node current and a mutex mu. In the nextNode method, we calculate the next node according to the rules of weighted polling. In the ServeHTTP method, we use a mutex to first select a node from the weighted nodes and create a reverse proxy instance using httputil.NewSingleHostReverseProxy. Finally, we call the proxy.ServeHTTP method to forward the request to the corresponding server for processing.

3. Summary

This article introduces how to use Golang to achieve load balancing on the Web server. We first gave a brief introduction to the basic concepts of load balancing, then implemented a simple load balancer using the reverse proxy provided by Golang's net/http package, and implemented load balancing using a weighted round-robin algorithm. I hope this article can help everyone understand the load balancing of the web server.

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