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When you try to ssh into a instance and it failed giving errors which says remote host identification changed, possibly you have tried to ssh into that earlier but either it's been mapped to a IP or dns name has been assigned to that can resolve this issue ..

Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that a host key has just been changed.
The fingerprint for the ECDSA key sent by the remote host is
Please contact your system administrator.
Add correct host key in /home/bijendra/.ssh/known_hosts to get rid of this message.
Offending ECDSA key in /home/bijendra/.ssh/known_hosts:23
  remove with: ssh-keygen -f "/home/bijendra/.ssh/known_hosts" -R
ECDSA host key for has changed and you have requested strict checking.
Host key verification failed.

In case you see these messages while you ssh into the server, the identity of that instance has changed. Clear your home_folder/.ssh/known_hosts with the entry of the instance and now ssh. Accept the new identification. Known_hosts is a file which keeps track of the remote servers which you access and enters automatically for the next time.


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