Patroni没有start和stop，但它有维护模式啊。
Patroni 为什么没有停止的功能
说实话，这个问题我也是比较纳闷的。很多高可用程序都拥有startup/stop的选项，但是Patroni没有这些选项。
因为开发软件的人认为Patroni 的主要目的和任务是运行高可用集群，停止和启动它是非常奇怪的事。而且从技术上来说，因为它通过在Patroni节点上运行的REST API进行通信，所以无法停止。
我个人觉得还有一个点Patroni他要和Etcd和watchdog进行通信，所以停止它确实不推荐。但是能不能手工停呢？我个人试过，只要把你的数据库关闭，然后在把Patroni进程kill也是可行的。但是有watchdog的情况就不清楚了，毕竟需要给狗投食，所以建议最好先关闭watchdog。
Patroni的维护模式
而Patroni使用paused选项就可以进入维护模式，接下来我们来测试一下维护模式。
[postgres@133e0e204e206 ~]$ patronictl -c /etc/patroni.yml list
+ Cluster: patnori-test (6962171552537974697) --+----+-----------+
| Member | Host | Role | State | TL | Lag in MB |
+-----------+---------------+---------+---------+----+-----------+
| postgres1 | 133.0.204.206 | Leader | running | 15 | |
| postgres2 | 133.0.204.207 | Replica | running | 15 | 0 |
| postgres3 | 133.0.204.208 | Replica | running | 15 | 0 |
+-----------+---------------+---------+---------+----+-----------+
[postgres@133e0e204e206 ~]$ patronictl -c /etc/patroni.yml pause
Success: cluster management is paused
[postgres@133e0e204e206 ~]$ patronictl -c /etc/patroni.yml list
+ Cluster: patnori-test (6962171552537974697) --+----+-----------+
| Member | Host | Role | State | TL | Lag in MB |
+-----------+---------------+---------+---------+----+-----------+
| postgres1 | 133.0.204.206 | Leader | running | 15 | |
| postgres2 | 133.0.204.207 | Replica | running | 15 | 0 |
| postgres3 | 133.0.204.208 | Replica | running | 15 | 0 |
+-----------+---------------+---------+---------+----+-----------+
Maintenance mode: on
我们在Leader节点打开维护模式。现在我们就能够正常的关闭Patroni节点了。
[postgres@133e0e204e206 ~]$ ps -ef | grep patroni
postgres 24311 1 0 Jun03 ? 00:03:28 /usr/local/bin/python3.9 /home/postgres/.local/bin/patroni /etc/patroni.yml
postgres 30373 26101 0 16:00 pts/1 00:00:00 grep --color=auto patroni
[postgres@133e0e204e206 ~]$ kill -9 24311
关闭了Patroni节点之后，在Replica节点上查询集群状态。
[postgres@133e0e204e207 ~]$ patronictl -c /etc/patroni.yml list
+ Cluster: patnori-test (6962171552537974697) --+----+-----------+-----------------+
| Member | Host | Role | State | TL | Lag in MB | Pending restart |
+-----------+---------------+---------+---------+----+-----------+-----------------+
| postgres2 | 133.0.204.207 | Replica | running | 15 | 0 | * |
| postgres3 | 133.0.204.208 | Replica | running | 15 | 0 | * |
+-----------+---------------+---------+---------+----+-----------+-----------------+
Maintenance mode: on
可以看到另外两个节点，没发生自动故障转移。数据库仍然保持稳定的运行。
你登录leader节点的postgresql数据库，可以正常执行操作，没发生切换。
[postgres@133e0e204e206 ~]$ psql
psql (13.2)
Type "help" for help.
postgres=# select pg_is_in_recovery();
pg_is_in_recovery
-------------------
f
(1 row)
此时我们就可以对Patroni进行升级等一系列维护操作，不会影响集群的使用，但是如果接下来出现问题，就需要你手工进行故障转移了。
还有一个应用场景是你可能要停止你的数据库进行维护，但是Patroni会自动立马迅速的拉起它，或者是进行故障转移，此时你不想让它拉起来。你也可以把状态设置成维护模式，然后停止数据库。我们来测试一下。
假设我现在的leader在节点3上。
[postgres@133e0e204e206 ~]$ patronictl -c /etc/patroni.yml list
+ Cluster: patnori-test (6962171552537974697) --+----+-----------+-----------------+
| Member | Host | Role | State | TL | Lag in MB | Pending restart |
+-----------+---------------+---------+---------+----+-----------+-----------------+
| postgres1 | 133.0.204.206 | Replica | running | 16 | 0 | |
| postgres2 | 133.0.204.207 | Replica | running | 16 | 0 | * |
| postgres3 | 133.0.204.208 | Leader | running | 16 | | * |
+-----------+---------------+---------+---------+----+-----------+-----------------+
我先把节点3进入到维护模式。
[postgres@133e0e204e208 ~]$ patronictl -c /etc/patroni.yml pause
Success: cluster management is paused
然后我把节点3的数据库停止。
[postgres@133e0e204e208 ~]$ psql
psql (13.2)
Type "help" for help.
postgres=# select pg_is_in_recovery();
pg_is_in_recovery
-------------------
f
(1 row)
postgres=# \q
[postgres@133e0e204e208 ~]$ pg_ctl stop
waiting for server to shut down.... done
server stopped
此时我把主库shutdown了，在维护模式下，数据库并没有被立马拉起来，也没有发生failover。
[postgres@133e0e204e208 ~]$ patronictl -c /etc/patroni.yml list
+ Cluster: patnori-test (6962171552537974697) --+----+-----------+-----------------+
| Member | Host | Role | State | TL | Lag in MB | Pending restart |
+-----------+---------------+---------+---------+----+-----------+-----------------+
| postgres1 | 133.0.204.206 | Replica | running | 16 | 0 | |
| postgres2 | 133.0.204.207 | Replica | running | 16 | 0 | * |
| postgres3 | 133.0.204.208 | Replica | stopped | | unknown | * |
+-----------+---------------+---------+---------+----+-----------+-----------------+
Maintenance mode: on
整个数据库集群，另外两个从库都只能是只读状态。我们可以在主库上做一些维护操作了，维护完了在把主库启动。最后把Patroni维护模式关闭，整个集群就完好如初。
[postgres@133e0e204e208 ~]$ pg_ctl start
waiting for server to start....2021-06-07 17:09:00.200 CST [4283] LOG: redirecting log output to logging collector process
2021-06-07 17:09:00.200 CST [4283] HINT: Future log output will appear in directory "log".
done
server started
[postgres@133e0e204e208 ~]$ patronictl -c /etc/patroni.yml list
+ Cluster: patnori-test (6962171552537974697) --+----+-----------+-----------------+
| Member | Host | Role | State | TL | Lag in MB | Pending restart |
+-----------+---------------+---------+---------+----+-----------+-----------------+
| postgres1 | 133.0.204.206 | Replica | running | 16 | 0 | |
| postgres2 | 133.0.204.207 | Replica | running | 16 | 0 | * |
| postgres3 | 133.0.204.208 | Leader | running | 16 | | * |
+-----------+---------------+---------+---------+----+-----------+-----------------+
Maintenance mode: on
[postgres@133e0e204e208 ~]$ patronictl -c /etc/patroni.yml resume
Success: cluster management is resume
[postgres@133e0e204e208 ~]$ patronictl -c /etc/patroni.yml list
+ Cluster: patnori-test (6962171552537974697) --+----+-----------+
| Member | Host | Role | State | TL | Lag in MB |
+-----------+---------------+---------+---------+----+-----------+
| postgres1 | 133.0.204.206 | Replica | running | 16 | 0 |
| postgres2 | 133.0.204.207 | Replica | running | 16 | 0 |
| postgres3 | 133.0.204.208 | Leader | running | 16 | |
+-----------+---------------+---------+---------+----+-----------+
后记
维护模式还是很重要的，不然咱们稍微想动一下，就有可能导致整个集群发生故障转移，这不要背维护的锅了吗？所以掌握Patroni的维护模式，就能够方便的进行各种维护任务。
参考链接：
https://github.com/zalando/patroni/issues/447