Nginx Concurrency Estimation

Estimation formula: {（?G）*1024-system} / request size

• ?G: Memory size (in GB)
• 1024: Standard memory capacity conversion factor (MB to GB)
• system: Memory occupied by the system and services, plus reserved memory
• request size: Size of a request, typically in KB for static content or MB for dynamic content

A 16-core 32GB server can handle over 40,000 concurrent connections for load balancing, with a maximum capacity of 50,000–60,000 connections, saturtaing file descriptors.

Stress Testing Tool AB

1. Installing AB

[root@nginx-lua ~]# yum install httpd-tools -y

2. Basic Usage

[root@nginx-lua ~]# ab -n 200 -c 2 http://127.0.0.1/

// -n: total number of requests
// -c: number of concurrent requests
// -k: enable keep-alive connections

3. Parameter Explanation

[root@Nginx-lua conf.d]# ab -n2000 -c2 http://127.0.0.1/index.html
...
Server Software:        nginx/1.12.2
Server Hostname:        127.0.0.1
Server Port:            80

Document Path:          /index.html
Document Length:        19 bytes

Concurrency Level:      200
# Total time spent
Time taken for tests:   1.013 seconds
# Total number of requests
Complete requests:      2000
# Number of failed requests
Failed requests:        0
Write errors:           0
Total transferred:      510000 bytes
HTML transferred:       38000 bytes
# Requests per second (total requests / total time)
Requests per second:    9333.23 [#/sec] (mean)
# Average time per request for the client
Time per request:       101.315 [ms] (mean)
# Average time per request for the server
Time per request:       0.507 [ms] (mean, across all concurrent requests)
# Transfer rate, useful for identifying network bottlenecks
Transfer rate:          491.58 [Kbytes/sec] received

Viewing Concurrent Connections and Connection States

1. Check Concurrent Requests and TCP Connection States of Web Servers (Nginx/Apache)

netstat -n | awk '/^tcp/ {++S[$NF]} END {for(a in S) print a, S[a]}'
netstat -n | awk '/^tcp/ {++state[$NF]} END {for(key in state) print key,"t",state[key]}'

Typical output:

LAST_ACK 5 (waiting for the last ACK)
SYN_RECV 30 (connection request received, waiting for confirmation)
ESTABLISHED 1597 (normal data transmission)
FIN_WAIT1 51 (application has initiated termination)
FIN_WAIT2 504 (other side agrees to release)
TIME_WAIT 1057 (waiting for termination packets to expire)

Description of TCP States

• CLOSED: No active or ongoing connection
• LISTEN: Server waiting for incoming connection
• SYN_RECV: A connection request arrived, waiting for acknowledgment
• SYN_SENT: Application started, attempting to open a connection
• ESTABLISHED: Normal data transmission state
• FIN_WAIT1: Application indicates it has finished
• FIN_WAIT2: Other side agrees to release
• ITMED_WAIT: Waiting for all packets to expire
• CLOSING: Both sides attempt to close simultaneously
• TIME_WAIT: Other side initiated a release
• LAST_ACK: Waiting for all packets to expire

2. Check Number of Running Processes for Nginx or Apache

ps -ef | grep nginx | wc -l
ps -ef | grep httpd | wc -l

3. Check Number of Established Connections to the Web Server

netstat -antp | grep 80 | grep ESTABLISHED -c