* Split web/worker duties with THERMOGRAPH_ROLE
Background work (the subscription notifier) is welded to the same process
that serves requests, so scaling the web tier to N replicas would also scale
notifier instances unless something restricts it further than leader
election alone.
Add THERMOGRAPH_ROLE (web|worker|all, default all - unchanged single-process
behavior). Every replica runs the same image; ROLE only gates whether a
process is allowed to own the notifier at all, layered on top of the
existing leader election: web replicas never start it even if they'd win
leader election, worker replicas start it if they win. The decision is
pulled into _should_run_notifier() so it's unit-testable without booting the
full app (DB init, places index, neighbor warmer).
Add a minimal /healthz liveness route (no DB/upstream I/O, not under BASE)
so a worker replica - which serves no real traffic - still has something
Swarm can health-check.
* Add the Swarm interim stack file, a pinnable TimescaleDB tag, and a Caddy health-gate
Three changes toward the hop-1 interim cutover, all inert until Track B
stands up the platform:
docker-stack.yml: the Swarm stack file for the interim cutover, distinct
from docker-compose.yml (today's plain-compose deploy, unaffected). Pulls a
pre-built image (IMAGE_TAG) instead of building in place; app/worker publish
no host port (127.0.0.1:8137:8137 has no Swarm equivalent - Swarm's routing
mesh publishes on 0.0.0.0, which would expose the plaintext app un-fronted),
reaching Caddy only over an MTU-lowered overlay network (VXLAN-over-WireGuard
needs a smaller MTU or large payloads silently stall); db is placement-
pinned to a labelled node; app/worker skip inline migrations
(RUN_MIGRATIONS=0) so the runbook's one-shot migrate task is the only thing
that ever runs Alembic; secrets are real Swarm secrets mounted at
/run/secrets, read by the entrypoint shim rather than plain env vars.
TIMESCALEDB_TAG: docker-compose.yml's db image now reads this (default
latest-pg18, today's behavior unchanged), wired through Terraform
(timescaledb_tag, default "latest-pg18") so it can actually be pinned to an
exact minor without hand-editing the host - required before any host of the
stack could replicate with another (a floating tag risks mismatched
extension minors, which blocks a physical replica and risks compressed-
chunk corruption on restore).
Caddy active health-gate: both the Terraform-rendered Caddyfile and the live
deploy/Caddyfile now health-check the app on the same cheap /healthz route
its own Docker HEALTHCHECK uses (now /healthz instead of the SSR homepage,
so it's cheap enough for a tight interval and works identically for a
worker replica, which serves no public traffic at all) - Caddy won't
forward into a container that's still booting or unhealthy.
Verified live: built and booted the real image via docker compose - both
containers report healthy via the new /healthz-based HEALTHCHECK, and GET /
still renders the full SSR homepage unchanged. Both Caddyfiles validated
with the real caddy binary. docker-stack.yml validated with docker compose
config (required-var guards fire with clear messages; secrets correctly
mount at /run/secrets/<name>, matching the entrypoint shim's mapping).
docker-compose.yml validated with and without TIMESCALEDB_TAG set, alongside
the existing openmeteo overlay. terraform validate + fmt clean.
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