DNS resolution optimization skills and practice of http.Transport in Go language

DNS resolution optimization skills and practice of http.Transport in Go language

Abstract:
When using Go language for network programming, we often need to use http.Transport to handle HTTP requests. In http.Transport, DNS resolution is a very important link, which has a great impact on the response time and overall performance of the request. This article will introduce some tips and practices for optimizing DNS resolution of http.Transport in Go language, and demonstrate it through code examples.

1. Set DNS cache
   By default, Go language http.Transport does not cache DNS resolution results, and DNS resolution is performed for each request. This can cause increased response times for requests, especially when a large number of requests are made. We can enable caching of DNS resolution by setting the DialContext of http.Transport. The example is as follows:

import (
    "net"
    "net/http"
    "time"
)

func main() {
    transport := &http.Transport{
        DisableKeepAlives: true,
        DialContext: (&net.Dialer{
            Timeout: time.Second * 30,
            KeepAlive: time.Second * 30,
            Resolver: &net.Resolver{
                PreferGo: true,
                Dial: (&net.Dialer{
                    Timeout:   time.Second * 5,
                    KeepAlive: time.Second * 5,
                }).Dial,
            },
        }).DialContext,
    }

    client := &http.Client{
        Timeout:   time.Second * 60,
        Transport: transport,
    }
    
    // 使用client发起HTTP请求
    // ...
}

In the above example, we enable DNS resolution of Go language by setting the Resolver in DialContext to net.Resolver and setting PreferGo to true. Additionally, we set appropriate timeouts, as well as global timeouts and connection keep-alive times.

2. Use a custom DNS parser
   The Go language's default DNS parser may not be suitable for certain scenarios, such as when resolving a large number of host names. In this case, we can use a custom DNS resolver to improve performance. The following is a simple example using the github.com/miekg/dns library:

import (
    "context"
    "net"
    "net/http"
    "time"

    "github.com/miekg/dns"
)

type CustomDialer struct {
    resolver *dns.Resolver
}

func (d *CustomDialer) DialContext(ctx context.Context, network, address string) (net.Conn, error) {
    host, port, _ := net.SplitHostPort(address)
    msg := new(dns.Msg)
    msg.SetQuestion(dns.Fqdn(host), dns.TypeA)
    in, err := d.resolver.ExchangeContext(ctx, msg, net.JoinHostPort(d.resolver.Preferred()...))
    if err != nil {
        return nil, err
    }
    if len(in.Answer) == 0 {
        return nil, fmt.Errorf("no answer found for %s", host)
    }
    a := in.Answer[0].(*dns.A)
    return (&net.Dialer{
        Timeout:   time.Second * 5,
        KeepAlive: time.Second * 5,
    }).DialContext(ctx, network, net.JoinHostPort(a.A.String(), port))
}

func main() {
    resolver := &dns.Resolver{
        PreferGo: true,
    }

    transport := &http.Transport{
        DisableKeepAlives: true,
        DialContext: (&CustomDialer{
            resolver: resolver,
        }).DialContext,
    }

    client := &http.Client{
        Timeout:   time.Second * 60,
        Transport: transport,
    }
    
    // 使用client发起HTTP请求
    // ...
}

In the above example, we define a CustomDialer type, which implements the DialContext method, using custom DNS resolution processor for analysis. We use the github.com/miekg/dns library to send a DNS request and get the IP address from the returned result, and then use net.Dialer to make the actual connection.

Conclusion:
By optimizing the DNS resolution of http.Transport, we can significantly improve the performance and response time of Go language network programming. In practical applications, appropriate optimization methods can be selected according to the scenario to improve system performance and stability.

Reference link:

• [Go Documentation](https://golang.org/pkg/net/http/)
• [github.com/miekg /dns](https://github.com/miekg/dns)

(Note: The above code examples are for reference only. Actual use requires appropriate modifications and adjustments according to the specific situation.)

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