Paano mo makakamit ang high availability sa PostgreSQL?

Question

Accepted Answer

**High availability (HA)** tegese tetep database kasedhiyan sanajan ana gagal — liwat **replication** (standby replicas), **automatic failover** (ngowahi replica nalika primary gagal), lan architecture kang leres. Tujuan: kurangi downtime lan ilang data, amarga database outages bisa mateni kabeh aplikasi.

## Fondasi: replication + automatic failover

```text
Primary ──(streaming replication)──▶ Standby replica(s)

If the PRIMARY fails:
  → a STANDBY is automatically PROMOTED to become the new primary (FAILOVER)
  → the application reconnects to the new primary → minimal downtime
→ Without HA, a primary failure = total database outage = application down.
```

Replication tetep standby replicas tetep sync; **automatic failover** deteksi primary gagal lan ngowahi replica — ngubah outage total dadi gangguan cendhak.

## HA tooling (otomasi failover)

```text
Patroni → the popular HA solution: manages failover, uses a consensus store (etcd/
  Consul/ZooKeeper) to coordinate, prevents split-brain
repmgr → replication and failover management
Managed Postgres (AWS RDS/Aurora, Cloud SQL, etc.) → built-in HA with automatic failover
→ These automate detection + promotion, which is hard to do safely by hand.
```

Manual failover alon lan ruwet, dadi HA tools (utawa managed services) otomasi kanthi aman — kalebu cegah **split-brain** (rong primaries terima writes, sing rusak data).

## Connection routing

```text
Applications need to find the CURRENT primary after a failover:
  → a load balancer / proxy (HAProxy, PgBouncer) or service discovery routes
    WRITES to the current primary and READS to replicas
  → after failover, routing updates to point to the new primary
```

## Key HA considerations

```text
✓ Synchronous replication → no data loss on failover (vs async's small loss window)
✓ Multiple replicas / multiple availability zones → survive zone failures
✓ Avoid SPLIT-BRAIN (two primaries) — consensus/fencing prevents it (critical for safety)
✓ Monitoring + health checks to detect failures quickly
✓ Test failover regularly (like backups, untested failover may not work)
→ Many teams use MANAGED Postgres for built-in, battle-tested HA.
```

## Kenapa iki penting

High availability penting pengetahuan kanggo ngoperasi sistem PostgreSQL **production-critical**, amarga database outages mateni kabeh aplikasi (database asring dadi dependensi paling kritis), dadi ngerti carane tetep Postgres kasedhiyan sanajan ana gagal iku pengetahuan senior-level berharga kanggo sistem kang bisa dipercaya.

Fondasi — **replication plus automatic failover** — iku sing ngubah primary database gagal (kang kayadene outage aplikasi total) dadi gangguan singkat, bisa dibenakake: standby replicas tetep sync, lan nalika primary gagal, replica diwahaken otomatis kanggo nggentos.

Ngerti **HA tooling** (Patroni — solusi populer ngkoordinasi failover liwat consensus store; repmgr; utawa managed cloud Postgres karo HA built-in) penting amarga otomasi failover kanthi aman rada angel kanggo gawe tangan.

Ngerti **key considerations** penting: **synchronous replication** kanggo ora ilang data nalika failover, **multiple replicas liwat availability zones** kanggo selamet zone gagal, lan utamane **cegah split-brain** (cegah rong primaries trima writes bersamaan, sing rusak data — risiko serius kang consensus/fencing cegah).

Ngerti **connection routing** (terangke aplikasi menyang primary saiki sawise failover, liwat load balancers/proxies) lan failover (kaya backups) kudu **tested** dadi pengetahuan praktis lengkap.

Ngerti kebanyakan tim pakai **managed Postgres** kanggo HA sing wis dikuji juga relevan.

Amarga database kasedhiyan kritis kanggo sistem production (outage mateni kabeh), lan amarga nggatek iku perlu ngerti replication, automatic failover, split-brain prevention, lan connection routing (utawa pakai managed HA), ngerti PostgreSQL high availability iku pengetahuan penting senior-level kanggo design sistem kang bisa dipercaya, resilient — karamukten penting kanggo production databases lan topik nuduhake ngerti carane bangun database infrastructure kang selamet gagal, dikarepake kanggo senior database/infrastructure roles.