Docker engine doesn't reply to any new request. That doesn't allow to run container for maintenance operations, like renew a Let's Encrypt certificate.
The Docker engine has been restarted at 16:47 UTC.
This restart wasn't handled very well by the iptables: containers daemons weren't reachable by front-end nginx. After a reset of the iptables configuration and a second restart of the docker service, the issue was solved.
At 16:55 UTC, all the containers worked again.
This doesn't affect the Docker containers running on Equatower.