honeyDueAPI/docs/deployment/08-database.md

08 — Database (Neon Postgres)

Summary

Authoritative user data lives in a Neon-managed Postgres database in AWS us-east-1. Connections use TLS (DB_SSLMODE=require). Schema is managed via GORM AutoMigrate inside the api binary, coordinated across replicas by a Postgres advisory lock to prevent concurrent migration attempts.

Why Neon

Decision matrix

At deploy time we considered:

Option	Setup effort	Monthly cost	Backup/PITR	Scale ceiling	Notes
Neon Launch	Zero (managed)	$5-15	Included	Large	Picked
Postgres on a Hetzner VPS	High	$8 (VPS)	Manual	Medium	More ops
AWS RDS	Medium	$30+	Included	Huge	Overkill, expensive
Supabase Free	Zero	$0	Limited	Small	Free tier has quota limits
CNPG on our k3s	High (Helm)	$0 (using cluster)	Self-rolled	Medium	Operational burden

Neon Launch won on:

• Serverless: scales compute to zero when idle (cheap)
• Branch databases: we can create dev/staging branches from prod in seconds
• Connection pooling built-in: PgBouncer on the hostname suffix -pooler
• Point-in-time recovery included (paid tier)
• Pay-as-you-go with a $5 minimum — fits a bootstrapped app

Connection details

Field	Value
Hostname	ep-floral-truth-amttbc5a-pooler.c-5.us-east-1.aws.neon.tech
Port	5432
Username	neondb_owner
Database	honeyDue (case-sensitive!)
TLS mode	require (enforced by Neon; app pg driver verifies)
Branch	production (Neon's concept — isolated DB within the project)

The database name is case-sensitive

Postgres identifiers are lowercase unless quoted. Neon's UI created the database as "honeyDue" (quoted, camelCase preserved). In prod.env / ConfigMap we must use exactly POSTGRES_DB=honeyDue — lowercase honeydue gets a database "honeydue" does not exist error. This bit us during the initial Swarm deploy (Chapter 19 §Neon DB name).

Connection pooling

Why it matters

Postgres is memory-hungry per connection (~5-10 MB each). 3 api replicas × DB_MAX_OPEN_CONNS=25 = up to 75 direct Postgres connections. Add the worker's 25. Neon's free tier caps at 100 concurrent connections; paid tiers much higher.

PgBouncer on Neon

Neon provides a built-in PgBouncer at the -pooler subdomain. The non-pooler endpoint (ep-floral-truth-amttbc5a.c-5.us-east-1...) is the direct compute endpoint and connects straight to Postgres, paying the full TCP+TLS+startup handshake on every cold connection. The -pooler endpoint multiplexes through PgBouncer in Neon's infrastructure.

We use the -pooler endpoint because the direct endpoint paid ~440ms per cold handshake on a transatlantic link, visible as 1500ms-tail spikes in /api/tasks/ traces. The pooler keeps backend Postgres connections warm in Neon's data center, so the only latency our Go pods see is one TCP+TLS to PgBouncer (already warm via our pool) plus one query round-trip.

Modes PgBouncer supports:

• session — one server connection held per client session (transparent)
• transaction — server connection released after each transaction (high-throughput)
• statement — per-statement (most aggressive; breaks many features)

Neon's pooler runs in transaction mode. This is compatible with GORM out of the box (we don't use session-level features like LISTEN/NOTIFY or session-scope advisory locks). Note: database.MigrateWithLock() needs the direct (non-pooler) endpoint because session-level advisory locks don't survive PgBouncer's per-transaction cycling — but the migration helper opens its own ad-hoc connection bypassing the configured pool, so this happens automatically. See MigrateWithLock in internal/database/database.go.

Connection pool settings

In config.yaml (rendered into ConfigMap → env vars):

database:
  max_open_conns: 25
  max_idle_conns: 20
  max_lifetime: "1800s"
  max_idle_time: "0s"

These map to Go database/sql pool settings:

• MaxOpenConns: 25 — at most 25 concurrent connections per replica.
• MaxIdleConns: 20 — keep up to 20 warm connections per replica ready to reuse. Bumped from 10 because the pooler tolerates many client connections cheaply, and the cost of a cold handshake (~440ms transatlantic) is far higher than the cost of holding an idle connection.
• MaxLifetime: 1800s — recycle connections after 30 min. Bumped from 600s; with the pooler keeping things warm, longer lifetime reduces churn.
• MaxIdleTime: 0s — never close idle connections. Lifetime drives recycling instead.

Pool warm-up at boot

database.Connect() issues 20 parallel PingContext calls immediately after opening the pool. This pre-establishes MaxIdleConns connections to the pooler so the first user request doesn't pay any handshake.

The warm-up is bounded by one round-trip time (~440ms cold), not one round-trip per connection — pings run concurrently. Confirmed in pod logs at boot:

{"level":"info","requested":20,"warmed":20,"message":"DB pool warm-up complete"}

If warm-up partially fails (e.g., 18/20 succeed), the pod still starts; the pool fills the rest under traffic. Failure to ping at all would be caught by the synchronous sqlDB.Ping() immediately before, which is fatal.

Worst-case connection count

3 api + 1 worker replicas × 25 conns = 100 peak. Right at Neon free tier's ceiling, with zero margin. This is a real risk — a spike that saturates the pool on all replicas simultaneously would exhaust Neon's limit.

Mitigations to consider:

• Drop DB_MAX_OPEN_CONNS to 15 → 60 peak. Safe on free tier.
• Upgrade to Neon Scale plan (1000+ connections).
• Rely on Neon's PgBouncer to multiplex — the raw backend connections to Postgres-proper are pooled, not our TCP connections to Neon.

Currently we trust Neon's pooler to handle the multiplexing and run with the default 25/10. If we hit connection errors in prod, adjust.

Schema management

GORM AutoMigrate

On startup, the Go API's cmd/api/main.go calls database.MigrateWithLock() which:

1. Opens a dedicated Postgres connection
2. SELECT pg_advisory_lock(1751412071) — acquires a session-level advisory lock on a hardcoded key
3. Calls db.AutoMigrate(&models.*{}) for every GORM model
4. SELECT pg_advisory_unlock(...) via deferred function
5. Close the connection

The advisory lock serializes migrations across replicas: when 3 api pods start simultaneously, one acquires the lock and migrates; the others block on the lock. Once the first finishes (≤2s for already- migrated schema, up to 90s on first cold boot), the next acquires and sees the schema is current (no-op migrate).

Why an advisory lock

Without it, concurrent CREATE TABLE IF NOT EXISTS ... statements from multiple replicas would race — Postgres usually handles it, but GORM's AutoMigrate also alters tables (adds columns, indexes) which can deadlock under concurrency.

The advisory lock pattern (also used by Rails + Django + Alembic) is the canonical solution.

The lock key

1751412071 is a hardcoded integer in internal/database/database.go. Arbitrary but unique — as long as nothing else in the Postgres instance uses the same advisory lock key, no conflicts.

First-boot behavior

On a fresh database (new Neon project), the first api pod runs through every model's CREATE TABLE statement. This is ~50 tables for honeyDue and takes ~90 seconds.

On a warm database (tables already exist), AutoMigrate is fast — typically under 2 seconds. It still runs (GORM checks every model against the schema) but finds no work to do.

Where this bit us

With 3 api pods starting simultaneously and migrations taking 90s first time, the lock queue for the last replica is ~180s. We needed a startupProbe grace of 240s to cover this without false restart loops. See Chapter 7 §startupProbe and Chapter 19 §MigrateWithLock.

Downside: no schema versioning

AutoMigrate can only add — new tables, new columns, new indexes. It won't drop columns, rename them, or change types destructively. For those we'd need raw SQL migrations (a tool like golang-migrate or dbmate).

Today: we accept that schema changes are additive-only. When we need destructive changes, we'd hand-write them.

What's in the database

Major tables (see honeyDueAPI-go/internal/models/):

Table	Purpose
auth_user	Users (Django legacy name kept for compatibility)
user_userprofile	Profile data
authtoken_token	API auth tokens
residence_residence	Properties users manage
task_task	Maintenance tasks
task_taskcompletion	Task completion history
contractor_contractor	Contractor contacts
documents_document	Document records (files in B2)
notification_notification	In-app notifications
subscription_usersubscription	IAP subscriptions
admin_users	Next.js admin panel users

See honeyDueAPI-go/docs/TASK_LOGIC_ARCHITECTURE.md for the task logic model details.

Backup and recovery

Neon's built-in

Neon Launch includes point-in-time recovery within the last 24h (longer on Scale plan). To restore:

1. Go to Neon console → project → Backups
2. Create a branch from a timestamp
3. Point the app at the new branch (change DB_HOST in our ConfigMap)

Done. No tape-wrangling.

What we don't have

• Off-site backup (if Neon itself is compromised, we have no exfil). A nightly pg_dump to Backblaze B2 would close this gap. TODO (Chapter 20).
• Tested DR drills. We've never actually restored from a Neon backup into a new branch and pointed the app at it. Should be routine; hasn't been exercised.

Migrations from old MyCrib/Casera data

honeyDue originally ran on a Django codebase (MyCrib / Casera-era). The schema inherits Django's naming (app_model table names, _id suffix foreign keys). The Go app's GORM models have TableName() methods that preserve this:

func (Task) TableName() string { return "task_task" }

This isn't ideal (GORM's default tasks would be cleaner), but changing would require a migration that renames every table — more risk than value.

Neon regions

Neon's default region for new projects is aws-us-east-1 (Virginia). Our DB is there. Latency from Nuremberg to us-east-1 is ~108ms one-way TCP-level (verified by nc -z -w 5 from hetzner1), so ~220ms RTT through Neon's pooler stack.

This is the slowest hop in our data flow. Every api request that needs a DB query pays this latency at least once. Sub-millisecond Postgres execution time (verified via EXPLAIN ANALYZE: 0.04-0.34 ms on every hot path) means wall-clock latency = network + Neon proxy overhead.

Optimizations layered on top to minimize round trips

We don't move the DB region (yet) but we cut the number of RTTs per request via:

1. Auth caching (Chapter 7 §Redis) — token + user lookups served from Redis (1-hour TTL) and per-pod in-memory cache (5-min TTL). On warm cache: 0 SQL round-trips for auth.
2. JOIN consolidation — two-step find residence-IDs → find tasks IN ids collapsed into a single query with a Postgres subquery. One RTT instead of two.
3. Single-query auth — token + user fetched in one INNER JOIN instead of GORM's two-query Preload pattern.
4. Residence-IDs Redis cache — cached per user with 5-min TTL, invalidated on Create/Delete/Join/Remove. Saves 1 RTT per /api/documents/, /api/contractors/, /api/residences/summary/ request.

After these, a fully-warm /api/tasks/ is 1 SQL round-trip total (~220ms wall-clock). Verified via Jaeger trace — see Chapter 15.

When this still matters

• Any cold-cache request still pays 2-3 RTTs (~500-700ms).
• Pod startup pays 1 RTT × 20 (warm-up), but that runs in parallel: ~440ms one-shot.

Long-term fix: migrate Neon to aws-eu-central-1 (Frankfurt) — drops RTT to ~5ms and brings warm-cache requests under 50ms. Tracked in docs/observability-plan.md and Chapter 18 §migration triggers.

Environment variables the app reads

From ConfigMap:

Var	Purpose
DB_HOST	Neon pooler hostname (-pooler suffix)
DB_PORT	5432
POSTGRES_USER	neondb_owner
POSTGRES_DB	honeyDue
DB_SSLMODE	require
DB_MAX_OPEN_CONNS	25
DB_MAX_IDLE_CONNS	20
DB_MAX_LIFETIME	1800s
DB_MAX_IDLE_TIME	0s (never close idle)

From Secret (honeydue-secrets):

Var	Purpose
POSTGRES_PASSWORD	Neon DB password

Operator cheat sheet

# Connect to Neon from workstation (requires psql + the password)
PGPASSWORD="<pw>" psql -h ep-floral-truth-amttbc5a.c-5.us-east-1.aws.neon.tech \
  -U neondb_owner -d honeyDue

# From a pod (lets you debug against the actual in-cluster network path)
kubectl exec -n honeydue -it deploy/api -- sh
# inside the pod (no psql by default, but wget + JSON API works)
wget -qO- http://127.0.0.1:8000/api/health/

# See current migration state (no direct CLI, but the api logs show it)
kubectl logs -n honeydue deploy/api | grep -i migration

# See active connections (run against Neon)
SELECT count(*), usename, state, application_name
FROM pg_stat_activity
GROUP BY usename, state, application_name;

References

• Neon docs
• Neon pricing
• Postgres advisory locks
• GORM AutoMigrate
• honeyDue task architecture (repo-local)