How to high concurency in Spring Boot - spring-boot

Question

I have a requirement to create a product which should support 40 concurrent users per second (I am new to working on concurrency)
To achieve this, I tried to developed one hello world spring-boot project.
i.e.,
spring-boot (1.5.9)
jetty 9.4.15
rest controller which has get endpoint
code below:
#GetMapping
public String index() {
return "Greetings from Spring Boot!";
}
App running on machine Gen10 DL360
Then I tried to benchmark using apachebench
75 concurrent users:
ab -t 120 -n 1000000 -c 75 http://10.93.243.87:9000/home/
Server Software:
Server Hostname: 10.93.243.87
Server Port: 9000
Document Path: /home/
Document Length: 27 bytes
Concurrency Level: 75
Time taken for tests: 37.184 seconds
Complete requests: 1000000
Failed requests: 0
Write errors: 0
Total transferred: 143000000 bytes
HTML transferred: 27000000 bytes
Requests per second: 26893.28 [#/sec] (mean)
Time per request: 2.789 [ms] (mean)
Time per request: 0.037 [ms] (mean, across all concurrent requests)
Transfer rate: 3755.61 [Kbytes/sec] received
Connection Times (ms)
min mean[+/-sd] median max
Connect: 0 1 23.5 0 3006
Processing: 0 2 7.8 1 404
Waiting: 0 2 7.8 1 404
Total: 0 3 24.9 2 3007
100 concurrent users:
ab -t 120 -n 1000000 -c 100 http://10.93.243.87:9000/home/
Server Software:
Server Hostname: 10.93.243.87
Server Port: 9000
Document Path: /home/
Document Length: 27 bytes
Concurrency Level: 100
Time taken for tests: 36.708 seconds
Complete requests: 1000000
Failed requests: 0
Write errors: 0
Total transferred: 143000000 bytes
HTML transferred: 27000000 bytes
Requests per second: 27241.77 [#/sec] (mean)
Time per request: 3.671 [ms] (mean)
Time per request: 0.037 [ms] (mean, across all concurrent requests)
Transfer rate: 3804.27 [Kbytes/sec] received
Connection Times (ms)
min mean[+/-sd] median max
Connect: 0 2 35.7 1 3007
Processing: 0 2 9.4 1 405
Waiting: 0 2 9.4 1 405
Total: 0 4 37.0 2 3009
500 concurrent users:
ab -t 120 -n 1000000 -c 500 http://10.93.243.87:9000/home/
Server Software:
Server Hostname: 10.93.243.87
Server Port: 9000
Document Path: /home/
Document Length: 27 bytes
Concurrency Level: 500
Time taken for tests: 36.222 seconds
Complete requests: 1000000
Failed requests: 0
Write errors: 0
Total transferred: 143000000 bytes
HTML transferred: 27000000 bytes
Requests per second: 27607.83 [#/sec] (mean)
Time per request: 18.111 [ms] (mean)
Time per request: 0.036 [ms] (mean, across all concurrent requests)
Transfer rate: 3855.39 [Kbytes/sec] received
Connection Times (ms)
min mean[+/-sd] median max
Connect: 0 14 126.2 1 7015
Processing: 0 4 22.3 1 811
Waiting: 0 3 22.3 1 810
Total: 0 18 129.2 2 7018
1000 concurrent users:
ab -t 120 -n 1000000 -c 1000 http://10.93.243.87:9000/home/
Server Software:
Server Hostname: 10.93.243.87
Server Port: 9000
Document Path: /home/
Document Length: 27 bytes
Concurrency Level: 1000
Time taken for tests: 36.534 seconds
Complete requests: 1000000
Failed requests: 0
Write errors: 0
Total transferred: 143000000 bytes
HTML transferred: 27000000 bytes
Requests per second: 27372.09 [#/sec] (mean)
Time per request: 36.534 [ms] (mean)
Time per request: 0.037 [ms] (mean, across all concurrent requests)
Transfer rate: 3822.47 [Kbytes/sec] received
Connection Times (ms)
min mean[+/-sd] median max
Connect: 0 30 190.8 1 7015
Processing: 0 6 31.4 2 1613
Waiting: 0 5 31.4 1 1613
Total: 0 36 195.5 2 7018
From above test run, I achieved ~27K per second with 75 users itself but it looks increasing the users also increasing the latency. Also, we can clearly note connect time is increasing.
I have requirement for my application to support 40k concurrent users (assume all are using own separate browsers) and request should be finished within 250 milliseconds.
Please help me on this

Answer 1

I am also not a grand wizard in the topic myself but here is some advice:
there is a hard limit how many request can handle one instance so if you want to support a lot of user you need more instance
if you work with multiple instance then you have to somehow distribute the requests among the instances. One popular solution is Netflix Eureka
if you don't want to maintain additional resources and the product will run in cloud then use the provided load balancing services (e.g. LoadBalancer on AWS)
also you can fine-tune your server's connection pool settings