The agent-plane server cert was issued by hand (server-pki.sh / docker exec
step ca certificate), which needs the step CLI on the host, re-specifies SANs
each time, and silently expires at the CA's 90-day cap — the exact failure that
just broke agent TLS (cert minted with a stale SAN, missing manager.fleet.lab).
Automate it:
- agent-cert-renewer sidecar (smallstep step-cli image, compose profile
cert-auto): issues the cert once from the co-located fleet step-ca, then
'step ca renew --daemon' rotates it before the cap. Renewal preserves the
subject + SANs, so SAN drift cannot recur. Chowns to the manager's nonroot
uid so the distroless manager reads the key. Opt-in + only valid where the CA
is co-located; server-pki.sh stays as the manual/remote-CA path.
- manager hot-reloads via GetCertificate (certreload.go): a rotated cert on
disk is picked up on the next handshake with no restart and no dropped agent
streams; a half-written pair keeps the last good cert serving. Unit-tested.
- defaults.env documents the cert-auto knobs; DEPLOY.md §2a recommends the
renewer and flags the mandatory manager.fleet.lab SAN.
