# =============================================================================
# AI Software Factory — PostgreSQL read replica (hot standby) — TASK-0135.
#
# Streams WAL from the primary (postgres/statefulset.yaml) via
# `pg_basebackup` (first boot, initContainer) + continuous logical→physical
# replication (standby.signal). The API's DATABASE_REPLICA_URL points at the
# pooler's `factory;reader` entry (pgbouncer.yaml) → this Service.
#
# Staleness contract (perf-report §6): the replica lags. `db.read()` serves
# tree/listing/search from it; permission + If-Match version checks + writes
# stay on the primary. A read-only hot standby rejects writes at the DB.
#
# The replica is a SEPARATE StatefulSet (its own PVC). It is NOT part of the
# PITR set — a replica loss is re-created by re-running the base backup, and
# PITR restores target a fresh instance (runbook §8.1), never the replica.
# =============================================================================
apiVersion: v1
kind: ConfigMap
metadata:
  name: factory-pg-replica-config
  labels:
    app.kubernetes.io/name: postgres
    app.kubernetes.io/component: replica
    app.kubernetes.io/part-of: ai-software-factory
data:
  # Empty file — its presence makes postgres start as a standby. Mounted at
  # $PGDATA/standby.signal after the base backup.
  standby.signal: ""
  # Streaming-replication connection to the primary. The standby runs as the
  # `factory` role (a SUPERUSER-ish app role) so it can stream WAL from the
  # primary's `factory` role. `primary_slot_name` is empty — with a single
  # replica a physical replication slot is optional; set it if you add more
  # standbys (wal-g PITR also uses slots, but those are restore-time only).
  standby.conf: |
    primary_conninfo = 'host=factory-db.factory.svc port=5432 user=factory password=%(REPLICA_PASSWORD)s application_name=factory-replica'
    primary_slot_name = ''
    hot_standby = on
    hot_standby_feedback = on
---
apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: postgres-replica
  labels:
    app.kubernetes.io/name: postgres
    app.kubernetes.io/component: replica
    app.kubernetes.io/part-of: ai-software-factory
spec:
  serviceName: factory-db-replica
  replicas: 1
  selector:
    matchLabels:
      app.kubernetes.io/name: postgres
      app.kubernetes.io/component: replica
  template:
    metadata:
      labels:
        app.kubernetes.io/name: postgres
        app.kubernetes.io/component: replica
    spec:
      # initContainer: first boot only. Base-backup the primary's data into
      # the PVC, then drop standby.signal + standby.conf in place. If the
      # standby.signal is already present (a restore), skip the base backup
      # (the volume already holds a valid standby data dir).
      initContainers:
        - name: pg-basebackup
          image: postgres:16-alpine
          command:
            - sh
            - -c
            - |
              set -e
              DATA="${PGDATA:-/var/lib/postgresql/data}"
              if [ -f "$DATA/standby.signal" ]; then
                echo "[replica-init] standby.signal present — reusing existing data dir"
                exit 0
              fi
              echo "[replica-init] base backup from primary (first boot)"
              mkdir -p "$DATA"
              su postgres -c "PGPASSWORD=\"\$REPLICA_PASSWORD\" pg_basebackup -h postgres.factory.svc -p 5432 -U factory -D $DATA -X stream -c fast"
              # standby.signal + standby.conf (from the mounted ConfigMap) are
              # placed by the entrypoint below (it owns $PGDATA).
          env:
            - name: PGDATA
              value: /var/lib/postgresql/data
            - name: REPLICA_PASSWORD
              valueFrom: { secretKeyRef: { name: factory-db, key: POSTGRES_PASSWORD } }
          volumeMounts:
            - name: pgdata
              mountPath: /var/lib/postgresql/data
      containers:
        - name: postgres
          image: postgres:16-alpine
          env:
            - name: PGDATA
              value: /var/lib/postgresql/data
            - name: POSTGRES_USER
              value: factory
            - name: POSTGRES_DB
              value: factory
            - name: REPLICA_PASSWORD
              valueFrom: { secretKeyRef: { name: factory-db, key: POSTGRES_PASSWORD } }
            # The official entrypoint sees a NON-EMPTY $PGDATA with
            # standby.signal → it starts the standby (no re-init). The
            # standby.conf is placed by the entrypoint's first-run branch
            # below; to be safe we also copy it in the initContainer.
          command:
            - sh
            - -c
            - |
              set -e
              DATA="${PGDATA:-/var/lib/postgresql/data}"
              # Place standby.signal + standby.conf if not already present.
              [ -f "$DATA/standby.signal" ] || cp /etc/pg-replica/standby.signal "$DATA/standby.signal"
              [ -f "$DATA/standby.conf" ]   || sed "s/%(REPLICA_PASSWORD)s/$REPLICA_PASSWORD/" /etc/pg-replica/standby.conf > "$DATA/standby.conf"
              # Run postgres as the postgres user (the official image's user).
              su postgres -c "pg_ctl -D $DATA -w -t 60 start"
              exec tail -f /dev/null
          ports:
            - name: postgres
              containerPort: 5432
          envFrom:
            - secretRef: { name: factory-db }
          readinessProbe:
            exec:
              command:
                - sh
                - -c
                - |
                  # A standby is ready when it can ACCEPT a connection and is
                  # in recovery (pg_is_in_recovery = 't').
                  [ "$$(su postgres -c "psql -tAc \"select pg_is_in_recovery()\" 2>/dev/null || true)") = "t" ]
            initialDelaySeconds: 5
            periodSeconds: 5
          resources:
            requests: { cpu: 250m, memory: 512Mi }
            limits:   { cpu: "1", memory: 2Gi }
          volumeMounts:
            - name: pgdata
              mountPath: /var/lib/postgresql/data
            - name: replica-conf
              mountPath: /etc/pg-replica
              readOnly: true
      volumes:
        - name: replica-conf
          configMap: { name: factory-pg-replica-config }
  volumeClaimTemplates:
    - metadata:
        name: pgdata
      spec:
        accessModes: ["ReadWriteOnce"]
        resources:
          requests:
            storage: 20Gi
---
apiVersion: v1
kind: Service
metadata:
  name: factory-db-replica
  labels:
    app.kubernetes.io/name: postgres
    app.kubernetes.io/component: replica
    app.kubernetes.io/part-of: ai-software-factory
spec:
  selector:
    app.kubernetes.io/name: postgres
    app.kubernetes.io/component: replica
  ports:
    - name: postgres
      port: 5432
      targetPort: 5432