Unable to Connect to the Docker Host

Sometimes the hardest part is just connecting! If you can’t even connect to the Docker host, there are a few steps to try. To rule out issues where the host might not be up, the Docker daemon might not be started, or port traffic might be blocked, first attempt to SSH into the virtual machine. If you can successfully run docker ps from an SSH client, you know the issue isn’t the Docker daemon.

Another common connectivity issue is port mapping. If your virtual machine is behind some form of load balancer, you might need to ensure both that the Docker port is opened (default of 2376) and that any application-specific ports, like port 80 for a Web server, are open.

Another common issue is Docker certificates. Ensure that you are using the correct Docker certificates by verifying the DOCKER_CERT_PATH as mentioned earlier in the chapter.