title: SYNC with master failed: -ERR unknown command 'SYNC'
body: <p>I was trying to dump my Redis data that is hosted via AWS.  I can log into the interactive mode via redis-cli, but when I tried dumping the data to an RDB file I received the following error in the title...</p>
  
  <p>user@awshost:~/TaoRedisExtract$ redis-cli -h myawsredis.amazonaws.com --rdb redis.dump.rdb
  SYNC with master failed: -ERR unknown command 'SYNC'</p>
  
  <p>I'm not sure if this is a bug, a configuration issue, or known/expected behavior for AWS redis?  I've searched and searched and not found any other reports of users getting this error message.</p>