각 개발 언어에 대한 DNS 캐시 구성 권장 사항

int getaddrinfo( const char *node, 
 const char *service,
 const struct addrinfo *hints,
 struct addrinfo **res);

//连接nscd
socket(PF_LOCAL, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0) = 3
connect(3, {sa_family=AF_LOCAL, sun_path="/var/run/nscd/socket"}, 110) = -1 ENOENT (No such file or directory)
close(3)

//读取 hosts 文件
open("/etc/host.conf", O_RDONLY)= 3
fstat(3, {st_mode=S_IFREG|0644, st_size=9, ...}) = 0
...
open("/etc/hosts", O_RDONLY|O_CLOEXEC)= 3
fcntl(3, F_GETFD) = 0x1 (flags FD_CLOEXEC)
fstat(3, {st_mode=S_IFREG|0644, st_size=178, ...}) = 0

//获取 resolv.conf 中 DNS 服务 IP
open("/etc/resolv.conf", O_RDONLY)= 3
fstat(3, {st_mode=S_IFREG|0644, st_size=25, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fef2abee000
read(3, "nameserver 114.114.114.114nn", 4096) = 25
...
//连到 DNS 服务，开始 DNS 查询
connect(3, {sa_family=AF_INET, sin_port=htons(53), sin_addr=inet_addr("114.114.114.114")}, 16) = 0
poll([{fd=3, events=POLLOUT}], 1, 0)= 1 ([{fd=3, revents=POLLOUT}])

#/etc/nsswitch.conf 部分配置
...
#hosts: db files nisplus nis dns
hosts:files dns
...

newfstatat(AT_FDCWD, "/etc/nsswitch.conf", {st_mode=S_IFREG|0644, st_size=510, ...}, 0) = 0
...
openat(AT_FDCWD, "/etc/nsswitch.conf", O_RDONLY|O_CLOEXEC) = 3

#include <sys/socket.h>
#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <arpa/inet.h>
#include <unistd.h>

int gethostaddr(char * name);

int main(int argc, char *argv[]){
if (argc != 2)
{
fprintf(stderr, "%s $host", argv[0]);
return -1;
}

int i = 0;
for(i = 0; i < 5; i++)
{
int ret = -1;
ret = gethostaddr(argv[1]);
if (ret < 0)
{
fprintf(stderr, "%s $host", argv[0]);
return -1;
}
//sleep(5);
}

return 0;
}

int gethostaddr(char* name){
struct addrinfo hints;
struct addrinfo *result;
struct addrinfo *curr;
int ret = -1;
char ipstr[INET_ADDRSTRLEN];
struct sockaddr_in*ipv4;

memset(&hints, 0, sizeof(struct addrinfo));
hints.ai_family = AF_INET;
hints.ai_socktype = SOCK_STREAM;

ret = getaddrinfo(name, NULL, &hints, &result);
if (ret != 0)
{
fprintf(stderr, "getaddrinfo: %sn", gai_strerror(ret));
return ret;
}

for (curr = result; curr != NULL; curr = curr->ai_next)
{
ipv4 = (struct sockaddr_in *)curr->ai_addr;
inet_ntop(curr->ai_family, &ipv4->sin_addr, ipstr, INET_ADDRSTRLEN);
printf("ipaddr:%sn", ipstr);
}

freeaddrinfo(result);
return 0;
}

int
Curl_getaddrinfo_ex(const char *nodename,
const char *servname,
const struct addrinfo *hints,
Curl_addrinfo **result)
{
...
error = getaddrinfo(nodename, servname, hints, &aihead);
if(error)
return error;
...
}

import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.URL;


public class HttpUrlConnectionDemo {

public static void main(String[] args) throws Exception {
String urlString = "http://example.my.com/";

int num = 0;
while (num < 5) {
URL url = new URL(urlString);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setRequestMethod("GET");
conn.setDoOutput(true);

OutputStream os = conn.getOutputStream();
os.flush();
os.close();

if (conn.getResponseCode() == HttpURLConnection.HTTP_OK) {
InputStream is = conn.getInputStream();
BufferedReader reader = new BufferedReader(new InputStreamReader(is));
StringBuilder sb = new StringBuilder();
String line;
while ((line = reader.readLine()) != null) {
sb.append(line);
}
System.out.println("rsp:" + sb.toString());
} else {
System.out.println("rsp code:" + conn.getResponseCode());
}
num++;
}
}
}

import java.util.ArrayList;
import java.util.List;

import org.apache.hc.client5.http.classic.methods.HttpGet;
import org.apache.hc.client5.http.entity.UrlEncodedFormEntity;
import org.apache.hc.client5.http.impl.classic.CloseableHttpClient;
import org.apache.hc.client5.http.impl.classic.CloseableHttpResponse;
import org.apache.hc.client5.http.impl.classic.HttpClients;
import org.apache.hc.core5.http.HttpEntity;
import org.apache.hc.core5.http.NameValuePair;
import org.apache.hc.core5.http.io.entity.EntityUtils;
import org.apache.hc.core5.http.message.BasicNameValuePair;

public class QuickStart {
public static void main(final String[] args) throws Exception {
int num = 0;
while (num < 5) {
try (final CloseableHttpClient httpclient = HttpClients.createDefault()) {
final HttpGet httpGet = new HttpGet("http://example.my.com/");
try (final CloseableHttpResponse response1 = httpclient.execute(httpGet)) {
System.out.println(response1.getCode() + " " + response1.getReasonPhrase());
final HttpEntity entity1 = response1.getEntity();
EntityUtils.consume(entity1);
}
}
num++;
}
}
}

# 默认缓存 ttl 在 jre/lib/security/java.security 修改，其中 0 是不缓存，-1 是永久缓存
networkaddress.cache.ttl=10

# 这个参数 sun.net.inetaddr.ttl 是以前默认值，目前已经被 networkaddress.cache.ttl 取代

package main

import (
"flag"
"fmt"
"io/ioutil"
"net/http"
"time"
)

var httpUrl string

func main() {
flag.StringVar(&httpUrl, "url", "", "url")
flag.Parse()
getUrl := fmt.Sprintf("http://%s/", httpUrl)

fmt.Printf("url: %sn", getUrl)
for i := 0; i < 5; i++ {
_, buf, err := httpGet(getUrl)
if err != nil {
fmt.Printf("err: %vn", err)
return
}
fmt.Printf("resp: %sn", string(buf))
time.Sleep(10 * time.Second)# 等待10s发起另一个请求
}
}

func httpGet(url string) (int, []byte, error) {
client := createHTTPCli()
resp, err := client.Get(url)
if err != nil {
return -1, nil, fmt.Errorf("%s err [%v]", url, err)
}
defer resp.Body.Close()

buf, err := ioutil.ReadAll(resp.Body)
if err != nil {
return resp.StatusCode, buf, err
}

return resp.StatusCode, buf, nil
}
func createHTTPCli() *http.Client {
readWriteTimeout := time.Duration(30) * time.Second
tr := &http.Transport{
DisableKeepAlives: true,//设置短连接
IdleConnTimeout: readWriteTimeout,
}
client := &http.Client{
Timeout: readWriteTimeout,
Transport: tr,
}
return client
}

//主要在fasthttp/tcpdialer.go中
type TCPDialer struct {
...
// This may be used to override DNS resolving policy, like this:
// var dialer = &fasthttp.TCPDialer{
//Resolver: &net.Resolver{
//PreferGo: true,
//StrictErrors: false,
//Dial: func (ctx context.Context, network, address string) (net.Conn, error) {
//d := net.Dialer{}
//return d.DialContext(ctx, "udp", "8.8.8.8:53")
//},
//},
// }
Resolver Resolver

// DNSCacheDuration may be used to override the default DNS cache duration (DefaultDNSCacheDuration)
DNSCacheDuration time.Duration
...
}

func main() {
// You may read the timeouts from some config
readTimeout, _ := time.ParseDuration("500ms")
writeTimeout, _ := time.ParseDuration("500ms")
maxIdleConnDuration, _ := time.ParseDuration("1h")
client = &fasthttp.Client{
ReadTimeout: readTimeout,
WriteTimeout:writeTimeout,
MaxIdleConnDuration: maxIdleConnDuration,
NoDefaultUserAgentHeader:true, // Don't send: User-Agent: fasthttp
DisableHeaderNamesNormalizing: true, // If you set the case on your headers correctly you can enable this
DisablePathNormalizing:true,
// increase DNS cache time to an hour instead of default minute
Dial: (&fasthttp.TCPDialer{
Concurrency:4096,
DNSCacheDuration: time.Hour,
}).Dial,
}
sendGetRequest()
sendPostRequest()
}

r := &dnscache.Resolver{}
t := &http.Transport{
DialContext: func(ctx context.Context, network string, addr string) (conn net.Conn, err error) {
host, port, err := net.SplitHostPort(addr)
if err != nil {
return nil, err
}
ips, err := r.LookupHost(ctx, host)
if err != nil {
return nil, err
}
for _, ip := range ips {
var dialer net.Dialer
conn, err = dialer.DialContext(ctx, network, net.JoinHostPort(ip, port))
if err == nil {
break
}
}
return
},
}

#!/bin/python

import requests

url = 'http://example.my.com/'

num = 0
while num < 5:
headers={"Connection":"close"} # 开启短连接
r = requests.get(url,headers = headers)
print(r.text)
num +=1

#!/usr/bin/env python
import httplib2
http = httplib2.Http()
url = 'http://example.my.com/'

num = 0
while num < 5:
loginHeaders={
'User-Agent': 'Mozilla/5.0 (Windows NT 5.1) AppleWebKit/537.36 (KHTML, like Gecko) Maxthon/4.0 Chrome/30.0.1599.101 Safari/537.36',
'Connection': 'close'# 开启短连接
}
response, content = http.request(url, 'GET', headers=loginHeaders)
print(response)
print(content)
num +=1

#!/bin/python

import urllib2
import cookielib

httpHandler = urllib2.HTTPHandler(debuglevel=1)
httpsHandler = urllib2.HTTPSHandler(debuglevel=1)
opener = urllib2.build_opener(httpHandler, httpsHandler)
urllib2.install_opener(opener)

loginHeaders={
'User-Agent': 'Mozilla/5.0 (Windows NT 5.1) AppleWebKit/537.36 (KHTML, like Gecko) Maxthon/4.0 Chrome/30.0.1599.101 Safari/537.36',
'Connection': 'close' # 开启短连接
}

num = 0
while num < 5:
request=urllib2.Request('http://example.my.com/',headers=loginHeaders)
response = urllib2.urlopen(request)
page=''
page= response.read()
print response.info()
print page
num +=1

listen-address=127.0.0.1#程序监听地址，务必指定本机内网或回环地址，避免暴露到公网环境
port=53 #监听端口
resolv-file=/etc/dnsmasq.d/resolv.conf#配置dnsmasq向自定义文件内的 nameserver 转发 dns 解析请求
cache-size=150#缓存记录条数，默认 150 条，可按需调整、适当增大
no-negcache #不缓存解析失败的记录，主要是 NXDOMAIN，即域名不存在
log-queries=extra #开启日志记录，指定“=extra”则记录更详细信息，可仅在问题排查时开启，平时关闭
log-facility=/var/log/dnsmasq.log #指定日志文件

#同时需要将本机 /etc/resolv.conf 第一个 nameserver 指定为上述监听地址，这样本机系统的 dns 查询请求才会通过 dnsmasq 代为转发并缓存响应结果。
#另 /etc/resolv.conf 务必额外配置 2 个 nameserver，以便 dnsmasq 服务异常时支持系统自动重试，注意 resolv.conf 仅读取前 3 个 nameserver