Does someone know a tool that creates a Certificate Authority and signs certificates with that CA? (…) just a tool that spits out the certificates and I manage them that way, instead of a whole service for managing certs.
You’re adding a root certificate to your systems that will effectively accept any certificate issued with your CA’s key. If your PK gets stolen somehow and you don’t notice it, someone might be issuing certificates that are valid for those machines. Also real CA’s also have ways to revoke certificates that are checked by browsers (OCSP and CRLs), they may employ other techniques such as cross signing and chains of trust. All those make it so a compromised certificate is revoked and not trusted by anyone after the fact.
Why not Let’s Encrypt?
that’s fair but if your only concern is about “I do not want any public CA to know the domains and subdomains I use” you get around that.
Let’s Encrypt now allows for wildcard so you can probably do something like *.network.example.org and have an SSL certificate that will cover any subdomain under network.example.org (eg. host1.network.example.org). Or even better, get a wildcard like *.example.org and you’ll be done for everything.
I’m just suggesting this alternative because it would make your life way easier and potentially more secure without actually revealing internal subdomains to the CA.
Another option is to just issue certificates without a CA and accept them one at the time on each device. This won’t expose you to a possibly stolen CA PK and you’ll get notified if previously the accepted certificate of some host changes.