Vault is great for just a PKI, even if you aren't using it for anything else. There are some tools that
just do PKI, but Vault works a real treat at it. Any Terraform backend that supports encryption + Terraform + Vault gives you such an amazing workflow. We use a mix of short and long certs, with different roles based on what's getting a cert.
For now, we have CRLs disabled on all short-lived backends, enabled on long-lived backends and we're actually looking at disabling storing short-lived certs in the storage system at all, and just cranking the TTL down to really truly short. We've tested it as low as 30m, but a more real-world max-ttl is 1 week, with individual apps setting it as low as they can handle. For reference we run more than 10 PKI backends, and adding one (or a bunch) more is just a little terraform snippet for us.
The way it works via hashicorp template land, is that you just plop
{{ with secret "name-of-pki/issue/name-of-role" "common_name=my.allowed.fqdn" "ttl=24h" }} {{ .Data.certificate }} {{ end }}
into your Nomad template stanza, or use consul-template directly as a binary, or use vault agent with it's template capability. You can get the CA chain if required the same way, just hitting a different PKI endpoint.
Also, as of Vault 1.4, Vault's internal raft backend is now production ready, making it a snap to run.
Try running through a few of the Vault quick-start guides, and replicating them in Terraform as much as possible. There's a few things TF does not handle gracefully last I checked (initial bootstrap), but you can get around that by using a null_resource or just handling that outside Terraform.