Comment by najeh for Best practice is to not have passwords on cloud instances. If you have several hundred instances to look after, you either give them the same password (bad for security) or you have to remember several hundred passwords (good luck). So, the standard practice is to use password-less ssh. You set up a keypair (openstack keypair create mykey > mykey.pem), launch the instance with the key (openstack server create --key-name mykey ...), and ssh into the instance using the private key (ssh -i mykey.pem ...). i suggest you learn about ssh and keys, and Nova and keypairs.

I acces to the instance and after a few time i lose this access and i can't ping the instance address. Where is the problem ? and show this error ssh: connect to host 192.168.x.x port 22: Connection refused