[toygres] Replica support - streaming replication

[affandar]

Repository

affandar/toygres

Current State

Toygres currently manages single-instance Postgres deployments with no replication.

Proposed Features

Add Replica API

client.add_replica(AddReplicaRequest {
    instance_id: "pg-prod-1".into(),
    replica_id: "pg-prod-1-replica-1".into(),
    replica_config: ReplicaConfig {
        size: "small".into(),
        region: "us-east-1".into(),
        replication_mode: ReplicationMode::Async, // or Sync
    },
}).await?;

Orchestration Flow

1. Provision replica VM/container
2. Configure replica Postgres (recovery.conf, primary_conninfo)
3. Take base backup from primary
4. Start replica in standby mode
5. Wait for initial sync
6. Register replica in instance state
7. Start replication lag monitoring

List Replicas

let instance = client.get_instance("pg-prod-1").await?;
for replica in &instance.replicas {
    println!("{}: lag={}ms, state={:?}", replica.id, replica.replication_lag_ms, replica.state);
}

See: proposals/toygres-improvements.md