Have problem on building the multinode hadoop cluster by using EC2

i built a 4 nodes Hadoop clusters based on EC2. Everything looks good until it run the command:

./start-dfs.sh

then i got :

Starting namenodes on [ec2-3-212-99-195.compute-1.amazonaws.com]ec2-3-212-99-195.compute-1.amazonaws.com: starting namenode, logging to /home/ec2-user/app/hadoop-2.6.0-cdh5.7.0/logs/hadoop-ec2-user-namenode-ip-172-31-80-245.outThe authenticity of host 'ip-172-31-91-40 (34.225.65.17)' can't be established.RSA key fingerprint is 84:64:4c:84:98:2b:c2:4b:ca:98:15:1d:10:6f:46:ce.Are you sure you want to continue connecting (yes/no)? The authenticity of host 'ip-172-31-83-169 (34.204.115.105)' can't be established.RSA key fingerprint is 84:64:4c:84:98:2b:c2:4b:ca:98:15:1d:10:6f:46:ce.Are you sure you want to continue connecting (yes/no)? ip-172-31-82-16: starting datanode, logging to /home/ec2-user/app/hadoop-2.6.0-cdh5.7.0/logs/hadoop-ec2-user-datanode-ip-172-31-82-16.out

One of the Datanode is running, but the other two didn't respondNamenode and SecondaryNamenode also can run, needs help,does someone know what happened?