# tidalDB on Kubernetes

How to run tidalDB on Kubernetes. Two manifest sets ship in this repo, mutually
exclusive per namespace:

- **[`k8s/`](../../k8s/)** — the hardened single-node **standalone** deployment
  (namespace `tidaldb`, `replicas: 1`). Apply with `kubectl apply -k k8s/`. This
  is the recommended default: a `StatefulSet` with a durable volume, the three
  health probes, metrics, secret-backed auth, and graceful rolling updates.
- **[`k8s/cluster/`](../../k8s/cluster/)** — the multi-region **cluster**
  reference (namespace `tidaldb-cluster`, `replicas: 3`, automatic election,
  quorum-ack writes, elastic membership). Apply with `kubectl apply -k
  k8s/cluster/`. Still `--experimental-cluster`-gated. See
  [Cluster mode on Kubernetes](#cluster-mode-on-kubernetes) below.

> ## Deploy the STANDALONE server, one replica (recommended default)
>
> tidalDB is single-node-first: the server wraps one embedded engine whose state
> (WAL + checkpoints + indexes) lives on a data dir. It scales **vertically**
> (a bigger pod), not by adding replicas — there is no shared-storage multi-writer
> mode, so `replicas: 1` in the standalone StatefulSet is load-bearing. Run one
> standalone pod, back it with a durable `PersistentVolume`, and recover from the
> WAL on restart (see [recovery](../ops/recovery.md)).
>
> **The standalone pod remains the recommended deployment.** The multi-region
> `cluster` mode is now genuinely HA — quorum-acked writes (m11p3), automatic
> election/failover (m11p4), and elastic membership (m11p5) all exist — but it is
> still `--experimental-cluster`-gated, so choose it deliberately when you need
> multi-node availability, and keep a single standalone pod when you do not. The
> cluster reference is [`k8s/cluster/`](../../k8s/cluster/); see
> [Cluster mode on Kubernetes](#cluster-mode-on-kubernetes).

## What's in `k8s/`

| File | Purpose |
|------|---------|
| `namespace.yaml` | The `tidaldb` namespace |
| `schema-configmap.yaml` | The schema YAML the server loads (`--schema`); edit for your signals |
| `statefulset.yaml` | The server: durable PVC, probes, security context, resources |
| `service.yaml` | Headless `Service` for stable DNS + in-cluster clients |
| `poddisruptionbudget.yaml` | `maxUnavailable: 0` — a drain can't silently kill the single node |
| `secret.example.yaml` | Template for the API-key secret (create the real one out-of-band) |
| `servicemonitor.yaml` | Optional Prometheus-Operator scrape config (apply separately) |
| `kustomization.yaml` | Ties the core resources together for `kubectl apply -k` |

## Prerequisites

- A Kubernetes cluster (1.25+) and `kubectl` pointed at it. For local testing,
  [`kind`](https://kind.sigs.k8s.io/) is used in the walkthrough below.
- A container registry the cluster can pull from (for real clusters), or a local
  image loaded into the node (for `kind`). The image is built from
  [`docker/deploy/Dockerfile`](../../docker/deploy/Dockerfile).
- A default `StorageClass` (for dynamic `PersistentVolumeClaim` provisioning).
  `kind`, GKE, EKS, and AKS all ship one.

## Deploy

### 1. Build and publish the image

```bash
# From the repo root — the build context must be the workspace root.
docker build -f docker/deploy/Dockerfile -t <registry>/tidaldb:<tag> .
docker push <registry>/tidaldb:<tag>
```

Set that reference in `k8s/statefulset.yaml` (`image:`), pinned by digest in
production (`@sha256:...`).

### 2. Create the namespace and the API-key secret

The secret is deliberately **not** in the kustomization so no key lands in git.
Create it directly:

```bash
kubectl create namespace tidaldb
kubectl -n tidaldb create secret generic tidaldb-api-key \
  --from-literal=api-key="$(openssl rand -hex 32)"
```

In production, manage it with External Secrets Operator, Sealed Secrets, or
Vault Agent instead. The StatefulSet injects it as `TIDAL_API_KEY` — clients
then send `Authorization: Bearer <key>` on every data route. **If the secret is
empty the server runs unauthenticated and logs a WARN — never do that on a
shared network.**

### 3. Edit the schema (optional)

`k8s/schema-configmap.yaml` carries the schema the server loads. Edit it to model
your signals, text fields, embedding slots, and (optionally) ranking profiles —
the format is documented in [server-deployment.md](../guides/server-deployment.md).
The schema is read once at boot; roll the StatefulSet to apply changes.

### 4. Apply

```bash
kubectl apply -k k8s/
kubectl -n tidaldb rollout status statefulset/tidaldb --timeout=180s
```

### 5. Verify

```bash
kubectl -n tidaldb port-forward statefulset/tidaldb 9400:9400 &
KEY=$(kubectl -n tidaldb get secret tidaldb-api-key -o jsonpath='{.data.api-key}' | base64 -d)

curl -s localhost:9400/health                       # {"ok":true,...}
curl -s localhost:9400/openapi.json | jq .info      # served API contract
curl -s -X POST localhost:9400/items \
  -H "Authorization: Bearer $KEY" -H 'Content-Type: application/json' \
  -d '{"entity_id":1,"metadata":{"title":"hello","category":"demo","created_at":"1700000000"}}'
curl -s -H "Authorization: Bearer $KEY" "localhost:9400/feed?profile=trending&limit=5"
```

## How the health probes map

The server exposes three unauthenticated endpoints, wired to the three probe
types in `statefulset.yaml`:

| Probe | Endpoint | Behavior |
|-------|----------|----------|
| `startupProbe` | `GET /health/startup` | 200 once the HTTP listener is up; high `failureThreshold` covers slow WAL replay / index load on large data dirs (see [capacity-planning](../ops/capacity-planning.md)) |
| `livenessProbe` | `GET /health/live` | 200 while the process is alive; restart if it stops answering |
| `readinessProbe` | `GET /health` | 200 ready / **503 while draining** — on SIGTERM the pod leaves the Service endpoints before it stops accepting |

## Rolling updates and graceful shutdown

On `kubectl rollout restart` (or any pod delete), the kubelet sends SIGTERM. The
server flips readiness to 503 (so it leaves the Service), drains in-flight
requests, then checkpoints and fsyncs the WAL before exit.
`terminationGracePeriodSeconds: 60` gives that room — raise it if your data dir
is large. Because there is one replica, a restart is a brief planned outage
while the new pod replays the WAL; the `PodDisruptionBudget` (`maxUnavailable:
0`) prevents an *involuntary* drain from taking the node down without operator
intent.

## Persistence and backup

The `volumeClaimTemplate` provisions a `PersistentVolumeClaim` (`/data`, 10Gi by
default — size it from [capacity-planning](../ops/capacity-planning.md)). The WAL
+ checkpoints there are the source of truth and survive pod restarts. For backup
and disaster recovery (snapshotting the PVC, restoring a corrupt data dir), see
[recovery](../ops/recovery.md).

## Metrics

The pod exposes Prometheus metrics on `:9091/metrics` (**unauthenticated** — it is
not exposed by the headless Service externally; keep it cluster-internal). Scrape
it one of two ways:

- **Prometheus Operator:** `kubectl apply -f k8s/servicemonitor.yaml` (requires the
  `monitoring.coreos.com` CRDs).
- **Plain Prometheus:** the pod carries `prometheus.io/scrape`, `prometheus.io/port`,
  and `prometheus.io/path` annotations.

Alert rules and a dashboard ship in [`docs/ops/prometheus-alerts.yaml`](../ops/prometheus-alerts.yaml)
and [`docs/ops/grafana-dashboard.json`](../ops/grafana-dashboard.json); see
[monitoring](../ops/monitoring.md).

## Local walkthrough with `kind`

This is the exact flow used to verify the manifests end-to-end:

```bash
# 1. Create a local cluster.
kind create cluster --name tidaldb

# 2. Build the image and load it into the kind node (no registry needed).
docker build -f docker/deploy/Dockerfile -t tidaldb:deploy .
kind load docker-image tidaldb:deploy --name tidaldb

# 3. Namespace + API-key secret.
kubectl create namespace tidaldb
kubectl -n tidaldb create secret generic tidaldb-api-key \
  --from-literal=api-key="$(openssl rand -hex 32)"

# 4. Apply and wait for ready.
kubectl apply -k k8s/
kubectl -n tidaldb rollout status statefulset/tidaldb --timeout=240s

# 5. Verify, then tear down.
kubectl -n tidaldb port-forward statefulset/tidaldb 9400:9400 &
curl -s localhost:9400/health
kind delete cluster --name tidaldb
```

The manifests set `image: tidaldb:deploy` with `imagePullPolicy: IfNotPresent`,
which is exactly what `kind load` + a local tag need. For a real cluster, swap in
your registry image.

> **`kind create cluster` fails with "could not find a log line that matches …
> Multi-User System"?** On Docker Desktop the node's `systemd` can die at boot
> with `Failed to create control group inotify object: Too many open files`
> (`docker logs <cluster>-control-plane` shows it). The Docker VM's inotify
> limits are too low; raise them in the VM kernel, then recreate:
>
> ```bash
> docker run --rm --privileged alpine sysctl -w fs.inotify.max_user_instances=8192
> kind delete cluster --name tidaldb && kind create cluster --name tidaldb
> ```
>
> This is a kind-on-Docker-Desktop prerequisite, unrelated to tidalDB.

## Troubleshooting

| Symptom | Likely cause |
|---------|--------------|
| Pod `Pending` | No default `StorageClass`, or the PVC can't bind — `kubectl -n tidaldb describe pvc data-tidaldb-0` |
| Pod `CrashLoopBackOff` at boot | Bad schema YAML in the ConfigMap, or a data dir from an incompatible schema — check logs; see [recovery § schema mismatch](../ops/recovery.md) |
| Pod never `Ready`, but `Running` | Readiness probe failing — `kubectl -n tidaldb logs statefulset/tidaldb`; a large data dir may need a longer `startupProbe` |
| `401 Unauthorized` on data routes | Wrong/empty `tidaldb-api-key` secret; clients must send `Authorization: Bearer <key>` |
| Writes lost after restart | Data dir not on the PVC — confirm `--data-dir /data` and the `data` volume mount |

## Cluster mode on Kubernetes

The cluster reference is [`k8s/cluster/`](../../k8s/cluster/): **ONE `StatefulSet`
named `tidaldb`, `replicas: 3`**, in its own namespace `tidaldb-cluster`. Each
pod is a region; the three pods (`tidaldb-0/1/2`) form the initial voter set.
This is real HA — automatic election/failover, quorum-acked writes, and
membership changes that ride the replicated log — but the mode is still
`--experimental-cluster`-gated (set via `TIDAL_ALLOW_EXPERIMENTAL_CLUSTER=1` in
the manifest). It is **mutually exclusive** with the standalone set per namespace:
they share the StatefulSet name `tidaldb`, and the standalone set's `replicas: 1`
is load-bearing. Deploy one or the other.

### Why one StatefulSet (not one per region)

Before m11p5, a pod bound its own `grpc_addr` literally, and a pod cannot bind a
Service ClusterIP — so each region needed a per-pod topology variant, defeating
the "every process parses the same file" contract. The m11p5 **bind/advertise
split** removes that: `grpc_addr` is the address peers *dial* (a per-pod headless
DNS name, re-resolved by tonic on every reconnect, so a rescheduled pod on a new
IP is reachable with no peer restart), while `grpc_bind` is the local socket
(`0.0.0.0:9601`). One topology ConfigMap names all three regions by their stable
pod DNS, and every pod mounts it unmodified.

### What's in `k8s/cluster/`

| File | Purpose |
|------|---------|
| `namespace.yaml` | The `tidaldb-cluster` namespace (mutually exclusive with `tidaldb`) |
| `topology-configmap.yaml` | The ONE bootstrap topology shared by all pods: 3 regions by per-pod DNS (`grpc_addr` advertised, `grpc_bind` `0.0.0.0`), `replication.ack: quorum`, `replication.reseed_self_restart: true`, the election block |
| `schema-configmap.yaml` | The schema YAML every region loads (`--schema`) |
| `statefulset.yaml` | `replicas: 3`, `podManagementPolicy: Parallel`, `TIDAL_REGION` from `POD_NAME`, durable PVC at `/data` with `--data-dir /data/db`, the three probes (readiness now cluster-aware), uid 10001, `terminationGracePeriodSeconds: 60`, topology spread, and the ordinal-branching scale-up wrapper |
| `service-peers.yaml` | Headless peer Service (`publishNotReadyAddresses: true`) — stable per-pod DNS, keeps not-ready joiners resolvable for peers |
| `service-client.yaml` | Client Service — readiness-gated, drops not-ready/joining/quarantined pods from load balancing |
| `poddisruptionbudget.yaml` | `maxUnavailable: 1` — a 3-voter cluster keeps quorum across one disruption |
| `secret.example.yaml` | Template for the `tidaldb-credentials` / `TIDAL_API_KEY` secret (create the real one out-of-band) |
| `kustomization.yaml` | Ties it together for `kubectl apply -k k8s/cluster/` (secret excluded) |

### The two Services

- **`tidaldb-peers`** (headless, `clusterIP: None`, `publishNotReadyAddresses:
  true`): gives each pod the stable DNS name
  `tidaldb-N.tidaldb-peers.tidaldb-cluster.svc.cluster.local`, which the topology
  advertises. `publishNotReadyAddresses: true` is load-bearing — a joiner is
  *not ready* until it first converges, but peers must still resolve it to feed
  it a snapshot + catch-up stream; without this the joiner could never reach a
  seed to become ready (a deadlock).
- **`tidaldb`** (client-facing, VIP, readiness-gated): the address in-cluster
  clients hit. Default readiness gating drops not-ready/joining/quarantined/
  draining pods, so a client is never routed to a node that is still catching up.

### The readiness predicate (cluster-aware `/health`)

The `readinessProbe` stays `GET /health`, but in cluster mode it is now
predicate-driven (m11p5 §4). `/health` returns **503** when the node is:

- shutting down (SIGTERM drain — leaves both Services before it stops accepting);
- **quarantined** (an m11p4 divergent leader-acked suffix — serves status and
  votes, refuses the data plane until reseeded);
- **removed / decommissioned** (a `Removed` membership record reached it, or a
  voter's typed `removed` signal told it so);
- a **joiner** (seed-join learner) or **install boot** (snapshot-reseeded) that
  has **not yet first-converged** — convergence means the boot catch-up pull
  completed at least once AND lag fell to `≤ learner_promote_lag` (hysteresis;
  **never** `lag == 0`, which an open-loop write load keeps perpetually false).
  Sticky-ready after the first convergence.

A **restarted, PVC-retained voter is Ready on today's terms** — no regression for
ordinary pod restarts. `GET /cluster/status/local` surfaces the inputs
(`lag_events`, `quarantined`, `role`, `term`, `reseed_required`) for diagnosis,
plus the `tidaldb_cluster_reseed_required` and `tidaldb_cluster_divergence`
gauges.

### Deploy the cluster

```bash
# 1. Build/publish an image whose runtime user is uid 10001 (matches the
#    securityContext so the PVC is writable). One image serves every subcommand.
docker build -f docker/deploy/Dockerfile -t <registry>/tidaldb:<tag> .
docker push <registry>/tidaldb:<tag>
#    Set image: in k8s/cluster/statefulset.yaml (pin by @sha256 in production).

# 2. Namespace + the credentials secret (stress/Ref-A shape: name
#    tidaldb-credentials, key TIDAL_API_KEY). Same key on EVERY pod and client.
kubectl create namespace tidaldb-cluster
kubectl -n tidaldb-cluster create secret generic tidaldb-credentials \
  --from-literal=TIDAL_API_KEY="$(openssl rand -hex 32)"

# 3. Apply and wait for the 3-pod voter set.
kubectl apply -k k8s/cluster/
kubectl -n tidaldb-cluster rollout status statefulset/tidaldb --timeout=300s

# 4. Confirm three reachable regions with low lag, and check each node's role.
kubectl -n tidaldb-cluster exec tidaldb-0 -- \
  curl -s localhost:9500/cluster/status | jq '.regions[] | {name, lag_events, reachable}'
for p in tidaldb-0 tidaldb-1 tidaldb-2; do
  kubectl -n tidaldb-cluster exec "$p" -- \
    curl -s localhost:9500/cluster/status/local | jq '{role, term, membership_role, lag_events}'
done
```

### Scale up (3 → N): seed-join as a learner, auto-promote

`kubectl scale` is the whole story — **no topology edits**. Pods with ordinal
`≥ 3` boot with `--seed` (the StatefulSet's ordinal-branching wrapper adds it
automatically) and learn their roster/id/term from a seed, joining as a
**learner**. The leader auto-promotes a learner to a voter once its durable mark
is within `learner_promote_lag` of the leader's frontier (or stops falling behind
for K rounds under sustained load).

```bash
# Grow to 5 voters. Pods tidaldb-3 and tidaldb-4 seed-join + auto-promote.
kubectl -n tidaldb-cluster scale statefulset/tidaldb --replicas=5
kubectl -n tidaldb-cluster rollout status statefulset/tidaldb --timeout=600s
# Watch the new members converge and promote (promotion_pending shows the lag):
kubectl -n tidaldb-cluster exec tidaldb-0 -- \
  curl -s localhost:9500/cluster/members | jq '.members[] | {id, name, role}'
```

A scaled pod still mounts the shared topology ConfigMap — a `--seed` boot
**requires** the local config for the behavioral knob blocks (`replication`,
`wal`, `election`, `timeouts`, `grpc_tls`); its `regions:` list is ignored for
the seed joiner's roster (the join response is authoritative).

### Scale down (N → fewer): remove verb FIRST, then scale

Decommission a member **before** removing its pod, so the cluster stops counting
it toward quorum cleanly. Remove the highest-ordinal members (StatefulSet deletes
lowest-ordinal-last on scale-down).

```bash
# Going 5 -> 3: decommission tidaldb-4, then tidaldb-3, then scale.
# Remove verb: POST /cluster/members/remove {"region": "<name>"} (any node
# forwards to the leader; one-at-a-time, quorum-commit-gated).
kubectl -n tidaldb-cluster exec tidaldb-0 -- curl -s -X POST \
  -H "Authorization: Bearer $KEY" -H 'Content-Type: application/json' \
  -d '{"region":"tidaldb-4"}' localhost:9500/cluster/members/remove
kubectl -n tidaldb-cluster exec tidaldb-0 -- curl -s -X POST \
  -H "Authorization: Bearer $KEY" -H 'Content-Type: application/json' \
  -d '{"region":"tidaldb-3"}' localhost:9500/cluster/members/remove
# Each Remove is delivered to the removed peer (which flips to 503 and stops
# campaigning) before its ship cell retires. Only then is it safe to scale.
kubectl -n tidaldb-cluster scale statefulset/tidaldb --replicas=3
```

Removing pods without the remove verb leaves zombie members the cluster still
expects — never scale down before decommissioning.

### Node / pod replacement

- **`kubectl delete pod tidaldb-N` (PVC retained):** the StatefulSet recreates
  the pod onto its existing PVC. It boots a follower, replays its WAL, and
  catches up via the `StreamSegments` stream (boot-time + the 30 s catch-up
  timer). No operator verb. This is the routine replace — already proven by the
  p4 leader-kill regression (lag → 0 within ~10 s).
- **PVC + pod delete (fresh reseed):** delete the PVC *and* the pod. The new pod
  comes up with an empty data dir, latches an install boot, and **reseeds via
  snapshot** (`FetchSnapshot` + stream) from the leader, then rejoins clean. Use
  this when the data dir is corrupt or the node fell behind a compacted leader.
  Readiness stays 503 until the snapshot install first converges.

### Self-healing reseed (quarantine / behind-compaction)

`replication.reseed_self_restart: true` (set in the topology ConfigMap) makes a
node that durably latches `reseed_required` (an m11p4 divergence quarantine, or a
typed `snapshot-required` refusal) drain and exit(0); the StatefulSet restarts it
and the **boot-time install** reseeds it via snapshot, clearing the quarantine
and the divergence gauge with no operator verb and no PVC wipe. The self-restart
is **refused** (loudly, in `/cluster/status/local` + the gauge) when the
remaining voters cannot sustain quorum without this node — exiting during a
2-voter window would be a total write outage. `POST /cluster/reseed` latches the
marker on demand.

### PodDisruptionBudget and graceful shutdown

`maxUnavailable: 1` lets a voluntary disruption (node drain, autoscaler, rolling
upgrade) take at most one pod at a time, preserving quorum (2 of 3). On SIGTERM a
pod flips readiness to 503 (leaving both Services), drains, lets the leader
lease/heartbeat windows lapse so a successor is elected cleanly, then checkpoints
+ fsyncs the WAL; `terminationGracePeriodSeconds: 60` covers the sequence.

### The exit-gate harness

The in-cluster load Jobs in [`tidal-stress/k8s/`](../../tidal-stress/k8s/) target
the cluster by per-pod DNS (`tidaldb-N.tidaldb-peers.tidaldb-cluster.svc.cluster.local:9500`),
in namespace `tidaldb-cluster`, reading the `tidaldb-credentials` secret. They
run the capacity ramp, the quorum-throughput gate (`stress-job-t2a.yaml`,
`--ack quorum`), and the leader-kill chaos drill (`stress-job-t2b.yaml`).

## See also

- [Server deployment guide](../guides/server-deployment.md) — config, auth, the served OpenAPI spec
- [Build a feed app](../guides/build-a-feed-app.md) — what to run against this server
- [Cluster runbook](cluster.md) — the multi-region mode's operational API (launch, promote, heal, reseed)
- [Monitoring](../ops/monitoring.md) · [Capacity planning](../ops/capacity-planning.md) · [Recovery](../ops/recovery.md)