Telnet to EC2 from another EC2 hosting robot framework scripts

Question

BACKGROUND:

We have many data services(DS) installed in different AWS EC2s. We are automating test cases for each of these using Robot Framework. We will be executing the test scripts from a specific EC2 instance where we have a tool setup. I have my robot script inside this specific EC2 and I need to 1st establish connection to my EC2 instances where one of the service is hosted.

ISSUE

I tried telnet and SSH but unlike telnet <IP add> <port> , here username is mandatory. I passed ec2-user and root, but it throws me authentication error. Can anyone guide me how to successfully establish connection between 2 EC2 instances so that I can run my test scripts successfully ?

Documentation      Robot Framework test script
Library            Telnet
*** Variables ***
${host}            10.231.XX.XX
${port}            11211
${username}        ec2-user
${password}        ${EMPTY}
*** Test Cases ***
Test Telnet
     Open Connection     ${host}
     Login               ${username}     ${password}     delay=1
     Execute Command     hostname
     Close All Connections