Environment & Prerequisites

Servers

You need four Linux servers (Ubuntu 24.04 LTS or 26.04 — this guide uses the PGDG repository, which supports both). Each needs a sudo-capable user and outbound internet access for package installation.

Hostname	Role	Example IP	vCPU	RAM	Disk
`pg-sv01`	PostgreSQL + Patroni + etcd	10.100.100.104	2	4 GB	32 GB
`pg-sv02`	PostgreSQL + Patroni + etcd	10.100.100.105	2	4 GB	32 GB
`pg-sv03`	PostgreSQL + Patroni + etcd	10.100.100.106	2	4 GB	32 GB
`pg-haproxy`	HAProxy entry point	10.100.100.103	2	2 GB	20 GB

Adjust IPs to your network — the rest of the guide uses the values above.

Name resolution

Patroni and etcd refer to nodes by name, so add static entries to /etc/hosts on all four servers:

sudo tee -a /etc/hosts >/dev/null <<'EOF'
10.100.100.103  pg-haproxy
10.100.100.104  pg-sv01
10.100.100.105  pg-sv02
10.100.100.106  pg-sv03
EOF

(If you manage DNS, A-records work just as well.)

Network ports

Open these between the nodes (we configure UFW per component as we go):

Port	Component	Direction
`2379`	etcd client API	among the 3 DB nodes + Patroni
`2380`	etcd peer	among the 3 DB nodes
`5432`	PostgreSQL	DB nodes ↔ each other (replication) + from HAProxy
`8008`	Patroni REST API	from HAProxy (health checks) + admin
`5432` / `5433`	HAProxy RW / RO	from your application clients
`7000`	HAProxy stats (optional)	from admins

Time sync

Make sure NTP/chrony is running on every node — replication and leader leases depend on reasonably accurate clocks. On Ubuntu, systemd-timesyncd is active by default.