Node js server and Apache ab tool: unexpected behavior

While testing a simple node server (written with Hapi.js):

'use strict';

var Hapi = require("hapi");
var count = 0;

const server = Hapi.server({
    port: 3000,
    host: 'localhost'
});

server.route({
    method: 'GET',
    path: '/test',
    handler: (request, h) => {
        count ++;
        console.log(count);
        return count;
    }
});

const init = async () => {
    await server.start();
};

process.on('unhandledRejection', (err) => {
    process.exit(1);
});

init();

start the server:

node ./server.js

run the Apache ab tool:

/usr/bin/ab -n 200 -c 30 localhost:3000/test

Env details:

OS: CentOS release 6.9
Node: v10.14.1
Hapi.js: 17.8.1

I found unexpected results in case of multiple concurrent requests (-c 30): the request handler function has been called more times than the number of requests to be performed (-n 200).

Ab output example:

Benchmarking localhost (be patient)

Server Software:
Server Hostname:        localhost
Server Port:            3000

Document Path:          /test
Document Length:        29 bytes

Concurrency Level:      30
Time taken for tests:   0.137 seconds
Complete requests:      200
Failed requests:        0
Write errors:           0
Total transferred:      36081 bytes
HTML transferred:       6119 bytes
Requests per second:    1459.44 [#/sec] (mean)
Time per request:       20.556 [ms] (mean)
Time per request:       0.685 [ms] (mean, across all concurrent requests)
Transfer rate:          257.12 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:        0    0   0.1      0       0
Processing:    15   17   1.5     16      20
Waiting:        2    9   3.9      9      18
Total:         15   17   1.5     16      21

Percentage of the requests served within a certain time (ms)
  50%     16
  66%     16
  75%     17
  80%     18
  90%     20
  95%     20
  98%     21
  99%     21
 100%     21 (longest request)

And the node server print out 211 log lines. During various tests the mismatch is variable but always present:

-n 1000 -c 1 -> 1000 log
-n 1000 -c 2 -> ~1000 logs
-n 1000 -c 10 -> ~1001 logs
-n 1000 -c 70 -> ~1008 logs
-n 1000 -c 1000 -> ~1020 logs

It seems that as concurrency increases, the mismatch increases.

I couldn’t figure out whether the ab tool performs more http requests or the node server responds more times than necessary.

Could you please help?