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.
Rename .env.example -> defaults.env and make it the committed defaults layer.
Compose reads defaults.env then .env (later wins) via COMPOSE_ENV_FILES, feeding
BOTH container env and ${...} interpolation — so a changed default here reaches
every run without re-copying, and .env shrinks to just overrides + secrets.
No compose service restructure: the existing interpolated environment: blocks
already build the container env; the layering just supplies their values from two
files. (env_file: directive alone wouldn't work — it doesn't feed the image-tag /
cross-service Influx / ACME_EMAIL interpolation this compose relies on.)
Docs (DEPLOY §1, compose header, README) updated: export
COMPOSE_ENV_FILES=defaults.env,.env, keep only secrets/overrides in .env.
Audiobuzz