Secure DNS resolution in Nginx reverse proxy

As network applications continue to develop, we need more and more security measures to protect our data and privacy. Among them, secure DNS resolution is a very important measure, which can protect us from being attacked by malicious DNS servers. It is also important to use secure DNS resolution in Nginx reverse proxy. This article will discuss secure DNS resolution in Nginx reverse proxy and explain how to set it up.

What is DNS resolution?

DNS (Domain Name System) resolution is the process of converting domain names into IP addresses. When you enter a domain name (such as "www.baidu.com") into the browser, the browser will request a DNS server to resolve the domain name and return the IP address of the domain name. The browser sends that IP address to the server to request the website's content.

DNS resolution is extremely important because most Web users do not know any IP address, but only the domain name of the website. A website's domain name is human-readable and serves as an identifier for users. Therefore, DNS resolution is the key to making it easier for us to remember and use domain names.

What is a reverse proxy?

A reverse proxy is a server setup that allows one server to respond to HTTP requests on behalf of another server. Reverse proxies are often used to improve the stability and performance of web servers.

When using a reverse proxy, the client's request will not be sent directly to the backend server. Instead, the request is sent to a reverse proxy server, which then forwards the request to the backend server. From the client's perspective, the request appears to be made directly from the reverse proxy server, not the backend server.

Reverse proxy servers are located on the Internet and forward requests to servers on the internal network. The advantage of this is that the servers of the internal network do not have to be directly exposed to the Internet, making them easier to manage and protect.

Nginx reverse proxy

Nginx is a lightweight, high-performance web server and reverse proxy server. It can handle both static and dynamic websites and provides some advanced features such as load balancing and caching services. Nginx's reverse proxy function is widely used in applications such as CDN, load balancing, and web server clusters.

The Importance of Secure DNS Resolution in Reverse Proxy

When we use Nginx to configure a reverse proxy, we need to forward the request to the backend server. This involves DNS resolution and IP address mapping. If a DNS server is compromised, requests may be forwarded to the wrong server or IP address, causing security issues.

To solve this problem, we can use secure DNS resolution. Secure DNS resolution protects us from malicious DNS servers. When using Nginx reverse proxy, it is recommended to use secure DNS resolution to prevent DNS pollution and DNS poisoning attacks.

Set up secure DNS resolution

The following are the steps to set up secure DNS resolution on the Nginx reverse proxy server:

1. Install DNS resolution tools: you can use dnspython and dns resolver and other tools. You can enter the following command at the command line to install dnspython:

pip install dnspython

2. Write a Python script: The following is an example Python script that uses dnspython to resolve domain names. You can save this script as a "secure_dns.py" file. In this example, the DNS server we are using is "8.8.8.8", which needs to be replaced with your own DNS server.

import dns.resolver
import argparse

parser = argparse.ArgumentParser(description='Secure DNS resolution')
parser.add_argument('--domain', dest='domain', required=True,
                   help='domain name')
args = parser.parse_args()

domain = args.domain

resolver = dns.resolver.Resolver()
resolver.nameservers = ['8.8.8.8']

answers = resolver.query(domain, 'A')
for rdata in answers:
    print('IP address:', rdata.address)

3. Use Python scripts in Nginx: You can use the ngx_http_substitutions_filter_module module to call Python scripts. This module enables Nginx to read Python scripts and insert the output into HTTP responses. Here is an example configuration using this module:

location / {
    resolver <IP address of DNS server> valid=60s;
    set $dns_output "";
    echo_before_body /usr/bin/python /path/to/secure_dns.py --domain=$host;
    sub_filter_once "<!--# echo var="dns_output" -->" $dns_output;
    proxy_pass http://<backend server>;
}

In this example, when Nginx receives an HTTP request, it calls the secure_dns.py script and then uses a reverse proxy to forward the request to the backend server .

Conclusion

When using Nginx reverse proxy, secure DNS resolution is a very important measure that can effectively protect our data and privacy. When setting up an Nginx reverse proxy, we should always keep this in mind and take the necessary security measures to ensure that our reverse proxy server always remains safe and reliable.

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