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I figured out the cause.  It is due to cors section that I added as below in otel-collector-config.yaml

http:
*         endpoint: 0.0.0.0:4318
*         cors:
*           allowed_origins:
*             - <http://localhost:3000>
*             - http://*.<http://ramco.com|ramco.com>
*             - https://*.<http://ramco.com|ramco.com>

<@U042HUD3CUW> `telnet` should work irrespective of the config above.
CORS only affects browsers.

Are you sure you have exposed the port `4318`?

Yes, self telnet works if I remove CORS section on the yaml and start the services.  So it is for sure that the CORS section that I introduced is causing it.