Oct 30, 2017

Fix: Cannot connect to the Docker daemon. Is the docker daemon running on this host?

First, you need to of course make sure your docker service is running:
sudo service docker status
You may need to add your current user to docker group, for example suppose you're logged in as ec2-user:
sudo usermod -aG docker ec2-user
You need to log out and log in again for it to take effect.
You can verify it by:
id ec2-user