ShaoZeMing commented on issue #3719:
URL: https://github.com/apache/apisix/issues/3719#issuecomment-788965474
I think this can also be used as a reference：
```
local resolver = require "resty.dns.resolver"
local http = require "resty.http"
function get_domain_ip_by_dns( domain )
-- 这里写死了google的域名服务ip，要根据实际情况做调整（例如放到指定配置或数据库中）
local dns = "8.8.8.8"
local r, err = resolver:new{
nameservers = {dns, {dns, 53} },
retrans = 5, -- 5 retransmissions on receive timeout
timeout = 2000, -- 2 sec
}
if not r then
return nil, "failed to instantiate the resolver: " .. err
end
local answers, err = r:query(domain)
if not answers then
return nil, "failed to query the DNS server: " .. err
end
if answers.errcode then
return nil, "server returned error code: " .. answers.errcode .. ": "
.. answers.errstr
end
for i, ans in ipairs(answers) do
if ans.address then
return ans.address
end
end
return nil, "not founded"
end
function http_request_with_dns( url, param )
-- get domain
local domain = ngx.re.match(url, [[//([\S]+?)/]])
domain = (domain and 1 == #domain and domain[1]) or nil
if not domain then
ngx.log(ngx.ERR, "get the domain fail from url:", url)
return {status=ngx.HTTP_BAD_REQUEST}
end
-- add param
if not param.headers then
param.headers = {}
end
param.headers.Host = domain
-- get domain's ip
local domain_ip, err = get_domain_ip_by_dns(domain)
if not domain_ip then
ngx.log(ngx.ERR, "get the domain[", domain ,"] ip by dns failed:",
err)
return {status=ngx.HTTP_SERVICE_UNAVAILABLE}
end
-- http request
local httpc = http.new()
local temp_url = ngx.re.gsub(url, "//"..domain.."/",
string.format("//%s/", domain_ip))
local res, err = httpc:request_uri(temp_url, param)
if err then
return {status=ngx.HTTP_SERVICE_UNAVAILABLE}
end
-- httpc:request_uri 内部已经调用了keepalive，默认支持长连接
-- httpc:set_keepalive(1000, 100)
return res
end
```
https://www.kancloud.cn/kancloud/openresty-best-practices/50474
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