作者：杭州美创科技有限公司
得益于PostgreSQL的开源特性，越来越多的第三方集群管理软件填补了PostgreSQL在集群方面的易用性和可靠性，patroni+etcd提供了一系列的集群管理方案。etcd负责集群状态信息的存放，用来联系各个节点，patroni负责为集群提供高可用服务，两者的集合为PostgreSQL集群提供了故障转移的高可用服务，它不仅配置简单，而且功能丰富：
- 支持手动和自动故障转移
- 支持一主多从、级联复制
- 支持同步、异步模式
- 支持使用watchdog防止脑裂
前期准备
节点规划。实验过程我们使用一主两从构建一套高可用环境。
关闭主机防火墙
# systemctl stop firewalld.service
# systemctl disable firewalld.service安装postgresql并搭建流复制环境（此步骤略）
在各个节点上部署etcd
安装必要的依赖包及etcd软件
# yum install -y gcc python-devel epel-release
# yum install -y etcd编辑配置文件（以下列出了需要修改的参数，并以主节点为例）
# vim /etc/etcd/etcd.conf
#[Member]
ETCD_DATA_DIR="/var/lib/etcd/node1.etcd"
ETCD_LISTEN_PEER_URLS="http://192.168.22.128:2380"
ETCD_LISTEN_CLIENT_URLS="http://192.168.22.128:2379,http://127.0.0.1:2379"
#[Clustering]
ETCD_INITIAL_ADVERTISE_PEER_URLS="http://192.168.22.128:2380"
ETCD_ADVERTISE_CLIENT_URLS="http://192.168.22.128:2379"
ETCD_INITIAL_CLUSTER="node1=http://192.168.22.128:2380,node2=http://192.168.22.129:2380, node3=http://192.168.22.130:2380"启动etcd集群，并设置开机自启动
# systemctl start etcd
# systemctl enable etcd在各个节点上部署python3
需要使用高版本的python来使用patroni服务，一般的linux环境内置了2.7版本的python环境，因此我们需要升级python，这里采用源码编译安装方式安装
# wget -c https://www.python.org/ftp/python/3.8.2/Python-3.8.2.tar.xz
# ./configure
# make
# make install删除原2.7版本的软连接，添加新的软链接以使用python3
# rm -f /usr/bin/python
# ln -s /usr/local/bin/python3 /usr/bin/python在各个节点上部署patroni
安装必要的依赖包和patroni软件
# pip3 install psycopg2-binary -i https://mirrors.aliyun.com/pypi/simple/
# pip3 install patroni -i https://mirrors.aliyun.com/pypi/simple/修改patroni配置文件（以主节点为例）
# vim /etc/patroni.yml
scope: pgsql
namespace: /pgsql/
name: pgsql_node2
restapi:
listen: 192.168.22.128:8008
connect_address: 192.168.22.128:8008
etcd:
host: 192.168.22.128:2379
bootstrap:
# this section will be written into Etcd:///config after initializing new cluster
# and all other cluster members will use it as a `global configuration`
dcs:
ttl: 30
loop_wait: 10
retry_timeout: 10
maximum_lag_on_failover: 1048576
master_start_timeout: 300
synchronous_mode: false
postgresql:
use_pg_rewind: true
use_slots: true
parameters:
listen_addresses: "0.0.0.0"
port: 5432
wal_level: logical
hot_standby: "on"
wal_keep_segments: 100
max_wal_senders: 10
max_replication_slots: 10
wal_log_hints: "on"
# archive_mode: "on"
# archive_timeout: 1800s
# archive_command: gzip < %p > /data/backup/pgwalarchive/%f.gz
# recovery_conf:
# restore_command: gunzip < /data/backup/pgwalarchive/%f.gz > %p
postgresql:
listen: 0.0.0.0:5432
connect_address: 192.168.22.128:5432
data_dir: /pgdata/patr2
bin_dir: /usr/pgsql-12/bin
# config_dir: /etc/postgresql/9.6/main
authentication:
replication:
username: repl
password: repl
superuser:
username: postgres
password: postgres
#watchdog:
# mode: automatic # Allowed values: off, automatic, required
# device: /dev/watchdog
# safety_margin: 5
tags:
nofailover: false
noloadbalance: false
clonefrom: false
nosync: false 配置patroni服务单元
# vim /etc/systemd/system/patroni.service
[Unit]
Description=Runners to orchestrate a high-availability PostgreSQL
After=syslog.target network.target
[Service]
Type=simple
User=postgres
Group=postgres
#StandardOutput=syslog
ExecStart=/usr/local/bin/patroni /etc/patroni.yml
ExecReload=/bin/kill -s HUP $MAINPID
KillMode=process
TimeoutSec=30
Restart=no
[Install]
WantedBy=multi-user.target启动patroni服务
# systemctl start patroni当然地，我们也可以直接使用patroni命令来启动patroni服务，配置服务单元是为了更方便使用。
#/usr/local/bin/patroni /etc/patroni.yml > patroni.log 2>&1 &集群环境使用
查看节点信息
# patronictl -c /etc/patroni.yml list
+ Cluster: pgsql (6972099274779350082)+------+---------+----+-----------+
| Member | Host | Role | State | TL | Lag in MB |
+-------------+---------------------+--------+---------+----+-----------+
| pgsql_node1 | 192.168.22.128:5432 | Leader | running | 3 | |
| pgsql_node2 | 192.168.22.129:5432 | | running | 3 | 0 |
| pgsql_node3 | 192.168.22.130:5432 | | running | 3 | 0 |
+-------------+---------------------+--------+---------+----+-----------+手动切换主从，选择某一可用的从节点，使其成为主节点角色
# patronictl -c /etc/patroni.yml switchover
Master [pgsql_node1]: pgsql_node1
Candidate ['pgsql_node2', 'pgsql_node3'] []: pgsql_node2
When should the switchover take place (e.g. 2021-06-20T11:42 ) [now]: now查看集群状态
# patronictl -c /etc/patroni.yml list
+ Cluster: pgsql (6972099274779350082)+------+---------+----+-----------+
| Member | Host | Role | State | TL | Lag in MB |
+-------------+---------------------+--------+---------+----+-----------+
| pgsql_node1 | 192.168.22.128:5432 | | running | 3 | 0 |
| pgsql_node2 | 192.168.22.129:5432 | Leader | running | 3 | |
| pgsql_node3 | 192.168.22.130:5432 | | running | 3 | 0 |
+-------------+---------------------+--------+---------+----+-----------+自动切换主从。重启node1节点所在主机。查看集群状态，node2自动提升为主，如果只是关闭节点实例，则patroni会再将数据库服务自动拉起。
# patronictl -c /etc/patroni.yml list
+ Cluster: pgsql (6972099274779350082)+------+---------+----+-----------+
| Member | Host | Role | State | TL | Lag in MB |
+-------------+---------------------+--------+---------+----+-----------+
| pgsql_node2 | 192.168.22.129:5432 | Leader | running | 3 | |
| pgsql_node3 | 192.168.22.130:5432 | | running | 3 | 0 |
+-------------+---------------------+--------+---------+----+-----------+初始化某一节点。当某一节点与主库不同步，或者节点异常运行时，可以使用此方法初始化节点信息以重新加入集群。
# patronictl -c /etc/patroni.yml reinit pgsql
+ Cluster: pgsql (6972099274779350082)+------+---------+----+-----------+
| Member | Host | Role | State | TL | Lag in MB |
+-------------+---------------------+--------+---------+----+-----------+
| pgsql_node1 | 192.168.22.128:5432 | | running | 3 | 0 |
| pgsql_node2 | 192.168.22.129:5432 | Leader | running | 3 | |
| pgsql_node3 | 192.168.22.130:5432 | | running | 3 | 0 |
+-------------+---------------------+--------+---------+----+-----------+
选择以下需要添加的节点名称：pgsql_node3
你确定要重新初始化成员 pgsql_node3？[y/N]：y
成功：为成员pgsql_node3执行初始化patroni是基于python开发的模板，etcd集群是按照Raft算法和协议开发的，是一个强一致性的、分布式的key-value数据库。两者的结合相辅相成，使得PostgreSQL集群在使用和维护过程中变得更便捷、更透明。