Are you trying to connect to a TLS-enabled daemon without TLS?

First, ensure the security group has a rule to open up port 2376 for docker.

This is because of the socket file permissions:

srw-rw---- 1 root docker 0 Mar 20 07:43 /var/run/docker.sock

sudo groupadd docker sudo gpasswd -a ${USER} docker sudo service docker restart sg docker -c "bash"

DO NOT RUN usermod WITHOUT "-a" as suggested in one of the other comments or it will wipe your additional groups setting and will just leave the "docker" group