如何在CentOS上实现PostgreSQL的高可用性

在CentOS上实现PostgreSQL的高可用性，可以采用多种方法。以下是一些常见的解决方案：

1. 使用Patroni

Patroni是一个用于管理PostgreSQL高可用性的工具，它基于Raft共识算法。

安装Patroni

sudo yum install -y python3-pip
sudo pip3 install patroni

配置Patroni

创建一个Patroni配置文件/etc/patroni.yml，示例配置如下：

scope: postgres
name: postgres_master
namespace: /db/
restapi:
  listen: 0.0.0.0:8008
  connect_address: 127.0.0.1:8008
etcd:
  host: 127.0.0.1:2379
  ttl: 30
  retry_timeout: 10
  max_lag_on_failover: 1048576
  postgresql:
    use_pg_rewind: true
    use_slots: true
    parameters:
      wal_level: replica
      max_connections: 100
      hot_standby: on
      synchronous_commit: off
      synchronous_standby_names: '*'
      wal_keep_segments: 8
      max_wal_senders: 4
      wal_sender_timeout: 60
      max_replication_slots: 4
      track_commit_timestamp: on
data_dir: /var/lib/postgresql/12/main
pg_hba:
  - host    replication     replicator     127.0.0.1/32            md5
  - host    all             all             0.0.0.0/0               md5
authentication:
  replication:
    username: replicator
    password: your_password
  superuser:
    username: postgres
    password: your_password

启动Patroni

sudo patroni /etc/patroni.yml

2. 使用Pgpool-II

Pgpool-II是一个中间件，提供负载均衡、故障转移和高可用性。

安装Pgpool-II

sudo yum install -y pgpool2

配置Pgpool-II

编辑/etc/pgpool2/pgpool.conf，示例配置如下：

backend_hostname0 = '192.168.1.101'
backend_port0 = 5432
backend_weight0 = 1
backend_data_directory0 = '/var/lib/postgresql/12/main'
backend_flag0 = 'ALLOW_TO_FAILOVER'

backend_hostname1 = '192.168.1.102'
backend_port1 = 5432
backend_weight1 = 1
backend_data_directory1 = '/var/lib/postgresql/12/main'
backend_flag1 = 'ALLOW_TO_FAILOVER'

listen_addresses = '*'
port = 9999
load_balance_mode = on
failover_command = '/usr/bin/pg_ctlcluster %d failover -m fast -o " -c gtm_start=%h:%p"'

启动Pgpool-II

sudo systemctl start pgpool2
sudo systemctl enable pgpool2

3. 使用Keepalived

Keepalived可以用于实现VIP（虚拟IP）的高可用性。

安装Keepalived

sudo yum install -y keepalived

配置Keepalived

编辑/etc/keepalived/keepalived.conf，示例配置如下：

vrrp_instance VI_1 {
    state MASTER
    interface eth0
    virtual_router_id 51
    priority 100
    advert_int 1
    authentication {
        auth_type PASS
        auth_pass 42
    }
    virtual_ipaddress {
        192.168.1.100
    }
}

virtual_server 192.168.1.100 5432 {
    delay_loop 6
    lb_algo rr
    lb_kind DR
    nat_mask 255.255.255.0
    persistence_timeout 50
    protocol TCP

    real_server 192.168.1.101 5432 {
        weight 1
        TCP_CHECK {
            connect_timeout 10
            connect_port 5432
        }
    }

    real_server 192.168.1.102 5432 {
        weight 1
        TCP_CHECK {
            connect_timeout 10
            connect_port 5432
        }
    }
}

启动Keepalived

sudo systemctl start keepalived
sudo systemctl enable keepalived

总结

以上是几种在CentOS上实现PostgreSQL高可用性的方法。选择哪种方法取决于你的具体需求和环境。Patroni和Pgpool-II提供了更全面的解决方案，而Keepalived则专注于VIP的高可用性。