There are several tools available that can be used to automate the upgrading of router and server operating systems. First of all, Chef, Ansible as well as Puppet are all not only configuration management tools, but all three can be used for the purpose of upgrading server OS or router firmware. Specifically:
Ansible: It is not only a configuration management tool, but it can also be used to automate software upgrades and manage patches for servers.
Chef: It provides tools for automating infrastructure management and can be used to manage software upgrades for servers.
Puppet: It is another configuration management tool that can also be used to manage software upgrades and patches for servers.
There are also some Linux-based tools as well including Ubuntu Landscape and Red Hat Network Satellite (used for Red Hat Enterprise Linxus systems). Spacewalk is still another open-source systems management solution that allows you to manage software packages and security updates for your servers.