Complete procedures with a way back.

Operate a Keepalived VRRPv3 pair with explicit priority, non-preemptive recovery, bounded health tracking, protocol-aware firewalling, packet evidence, split-brain fencing, and tested failover.

Deploy two supported Kea 3.0 LTS DHCPv4 peers in hot-standby mode with identical subnet policy, durable independent lease stores, fixed-address reservations, peer-only native HA listeners, automatic takeover guarded against split brain, and a controlled lease resynchronization path.

Build a deterministic TypeScript router that prefers local Ollama, permits OpenAI cloud only for eligible data with explicit per-request approval, checks provider capabilities and application-level validation evidence, fails over without loops or silent egress, and records content-free HMAC audit events.

Harden an existing three-member MongoDB 8.2 replica set, prove majority durability and client discovery, perform a planned election and bounded secondary outage, and reconcile real application-level evidence.

Build a redundant active-backup bond, carry a tagged service VLAN over it, terminate the host address on a Linux bridge, and introduce the topology through `netplan try` with automatic rollback, console recovery, and explicit switch-side evidence.

Build an authorized two-server DHCPv4 service with reviewed IPAM, inactive-first scope creation, internal DNS options, shared secure updates, reservations, load-balanced failover, relay and maintenance tests, and isolated recovery.

Deploy three independent Redis Sentinels around a TLS/ACL-protected Redis Open Source 8.8 primary and two replicas, prove quorum versus majority, validate Sentinel-aware clients and test promotion, fencing and backup restore.

Build and operate a PostgreSQL 18.4 hot standby with bounded WAL retention, verified lag, explicit fencing, planned promotion, endpoint cutover, and safe rewind or rebuild.