3 Reasons Why You Shouldn't Use Public CAs for Internal Infrastructures.
Public web certificate authorities like Let’s Encrypt were not designed to support internal use cases. What you need is a private certificate authority.
The deal with Registration Authorities, and what they do for you with Smallstep Certificate Manager
We’ve launched an ACME Registration Authority quickstart guide to help you easily automate certificate issuance and renewal to endpoints within walled-off networks. Read up on Registration Authorities and why may need them.
SSH vs. X.509 Certificates

SSH vs. X.509 Certificates

By: Linda Ikechukwu

Although SSH certificates are the most secure way to regulate SSH access, they are underutilised. They’re also frequently confused with X.509 (aka TLS) certificates. This article explains what SSH certificates are, why you should be using them, and how they differ from their more popular X.509 counterparts.