node-ansible fails to connect to the host when multiple connections coexist - node.js

Question

I have an API server which may trigger multiple node-ansibles simultaneously to connect to a remote machine to do something.
Here's the node.js code:
// app.js
const Ansible = require('node-ansible')
let ansibleNum = 10
for (let i = 0; i < ansibleNum; i += 1) {
let command = new Ansible.Playbook().playbook('test')
command.inventory('hosts')
command.exec()
.then(successResult => {
console.log(successResult)
})
.catch(err => {
console.log(err)
})
}
And the ansible playbook:
# test.yml
---
- hosts: all
remote_user: ubuntu
become: true
tasks:
- name: Test Ansible
shell: echo hello
register: result # store the result into a variable called "result"
- debug: var=result.stdout_lines
As ansibleNum increases, the probability of the failure of ansible playbook also increases.
The failure message is:
fatal: [10.50.123.123]: UNREACHABLE! => {"changed": false, "msg": "Failed to connect to the host via ssh: Shared connection to 10.50.123.123 closed.\r\n", "unreachable": true}
I've read another similar question here, but the solutions provided by it doesn't work in my case.
Another way to trigger the problem is by executing
ansible-playbook -i hosts test.yml & ansible-playbook -i hosts test.yml.
This command runs ansible without node.js.
I've pushed the code to github. You can download it directly.
Anyone knows why the shared connection got closed?
I've set ControlMaster argument to auto by following the document here.

Answer 1

It's strange that setting the connection type to paramiko solves my problem.
Here's the config file located in ~/.ansible.cfg:
[defaults]
transport = paramiko
Based on this document, it seems that paramiko doesn't support persistent connection.
I'm still confused about why this setting solves my problem.