Hi, I'm looking for something which I can use to monitor and control multiple servers from one location. For example, to check for updates and update all server at once. Update firewall rules at once, etc? Thanks.
Well, then you can use landscape.canonical.com which is made by the company behind Ubuntu. It also exists in a open source version, which supports up to 10 servers.
Otherwise there's Foreman, Ansible, Puppet and probably many more.
https://www.hashicorp.com/ has a great set of tools.
Packer: https://www.packer.io/docs/builders/digitalocean.html
Terraform: https://www.terraform.io/docs/providers/do/index.html
Vault: https://www.vaultproject.io
Nomad: https://www.nomadproject.io
Consul: https://www.consul.io
They work well with shell, ansible, chef, etc...
Which OS? Ubuntu, CentOS, FreeBSD, ... or maybe cross platform?
Ubuntu :-)