HTTP Status Codes

HTTP response status codes are three-digit numbers that indicate the outcome of a request. Common status codes include:

• 200: Success
• 301: Permanent redirect
• 302: Temporary redirect
• 304: Browser cache (not modified)
• 403: Forbidden (permission denied)
• 404: Resource not found
• 500: Internal server error (server code error)
• 502: Bad gateway (upstream resource not found)
• 504: Gateway timeout

Request and Response Headers

When a browser (client) acecsses a website, it sends request headers, and the server responds with its own headers. Below is an example breakdown:

// 1. Overview
Request URL: http://www.52wiki.cn/static/bootstrap/css/bootstrap.min.css
Request Method: GET
Status Code: 200 OK (from memory cache)
Remote Address: 61.184.215.226:80

// 2. Client Request Headers
Accept: text/html,application/xhtml+xml,...
Accept-Encoding: gzip, deflate
Accept-Language: zh-CN,zh;q=0.9
Cache-Control: max-age=0
Connection: keep-alive
Host: www.52wiki.cn
If-Modified-Since: Tue, 04 Dec 2018 09:58:20 GMT
If-None-Match: "a49-56b5ce607fe00"
Upgrade-Insecure-Requests: 1
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64)...
"--- empty line ---"
"--- request body ---"

// 3. Server Response Headers
HTTP/1.1 304 Not Modified
Date: Fri, 14 Sep 2018 09:14:28 GMT
Server: Apache/2.4.6 (CentOS) PHP/5.4.16
Connection: Keep-Alive
Keep-Alive: timeout=5, max=100
ETag: "a49-56b5ce607fe00"
"--- empty line ---"
"--- response body ---"

Nginx Log Statistics

Use the following command-line tools to analyze Nginx access logs (access.log):

• Count unique IPs (UV):

  awk '{print $1}' access.log | sort | uniq -c | wc -l
  

• Count total requests (PV):

  awk '{print $7}' access.log | wc -l
  

• Find most requested URLs:

  awk '{print $7}' access.log | sort | uniq -c | sort -n -k 1 -r | more
  

• Find most frequent IP addresses:

  awk '{print $1}' access.log | sort | uniq -c | sort -n -k 1 -r | more