Running:
yum-config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo
Produces:
Could not fetch/save url https://download.docker.com/linux/centos/docker-ce.repo to file /etc/yum.repos.d/docker-ce.repo:
[Errno 14] curl#60 - "Peer's Certificate issuer is not recognized."
I encountered this and solved it with
yum reinstall ca-certificates