已有的一个 MySQL PXC 集群环境，因为种种原因仅剩一个节点 node1，需要新增一个集群节点 node2。
node1 版本：donor version (8.0.21)
node2 版本：local version (8.0.32)
大致步骤：
1、node2 配置部署新版本的集群环境；
2、node2 配置/etc/my.cnf
拷贝 node1 的配置文件，仅需修改serverid、nodename
3、node2 准备数据目录，确保目录为空
4、node2 启动服务
会提示报错，需要将 node1 的 *.pem 文件拷贝到新节点，再次启动即可。
本次遇见一个低级错误，顺便看一下启动过程日志如下：
开始是使用那些pem文件握手连接，并执行数据同步，之后是升级：
2023-07-26T01:47:42.264423Z 1 [System] [MY-013413] [Server] Data dictionary upgrade from version '80021' to '80023' completed.
2023-07-26T01:47:50.295523Z 4 [System] [MY-013381] [Server] Server upgrade from '80021' to '80032' completed.
后面的启动尽管报错，但无需再次升级数据：
2023-07-26T01:50:51.621940Z 0 [Note] [MY-000000] [WSREP-SST] Proceeding with SST.........
2023-07-26T01:50:51.670240Z 0 [Note] [MY-000000] [WSREP-SST] ............Waiting for SST streaming to complete!
2023-07-26T01:51:15.992054Z 0 [Note] [MY-000000] [Galera] 0.0 (node1): State transfer to 1.0 (node2) complete.
2023-07-26T01:51:15.993423Z 0 [Note] [MY-000000] [Galera] Member 0.0 (node1) synced with group.
2023-07-26T01:51:15.998986Z 0 [Note] [MY-000000] [WSREP-SST] Preparing the backup at /mysql/pxc/data//sst-xb-tmpdir
2023-07-26T01:51:17.808995Z 0 [Note] [MY-000000] [WSREP-SST] Moving the backup to /mysql/pxc/data/
2023-07-26T01:51:17.929261Z 0 [Note] [MY-000000] [WSREP-SST] Running post-processing...........
2023-07-26T01:51:17.938459Z 0 [Note] [MY-000000] [WSREP-SST] Opting for mysql_upgrade (sst): local version (8.0.32) != donor version (8.0.21)
2023-07-26T01:51:18.030688Z 0 [Note] [MY-000000] [WSREP-SST] Waiting for server instance to start..... This may take some time
2023-07-26T01:51:31.230189Z 0 [ERROR] [MY-000000] [WSREP-SST] ******************* FATAL ERROR **********************
2023-07-26T01:51:31.230243Z 0 [ERROR] [MY-000000] [WSREP-SST] Failed to start the mysql server that checks for async replication.
2023-07-26T01:51:31.230251Z 0 [ERROR] [MY-000000] [WSREP-SST] Check the parameters and retry
2023-07-26T01:51:31.230255Z 0 [ERROR] [MY-000000] [WSREP-SST] Line 521 pid:6129
2023-07-26T01:51:31.232347Z 0 [ERROR] [MY-000000] [WSREP-SST] ------------ mysql error log (START) ------------
---- Starting the MySQL server used for post-processing ----
2023-07-26T01:51:18.237305Z 0 [Warning] [MY-011068] [Server] The syntax 'wsrep_slave_threads' is deprecated and will be removed in a future release. Please use wsrep_applier_threads instead.
2023-07-26T01:51:18.237360Z 0 [Warning] [MY-011068] [Server] The syntax 'skip_slave_start' is deprecated and will be removed in a future release. Please use skip_replica_start instead.
2023-07-26T01:51:18.237435Z 0 [Warning] [MY-010097] [Server] Insecure configuration for --secure-file-priv: Current value does not restrict location of generated files. Consider setting it to a valid, non-empty path.
2023-07-26T01:51:18.237441Z 0 [Warning] [MY-010097] [Server] Insecure configuration for --secure-log-path: Current value does not restrict location of generated files. Consider setting it to a valid, non-empty path.
2023-07-26T01:51:18.237480Z 0 [Warning] [MY-000000] [WSREP] Node is not a cluster node. Disabling pxc_strict_mode
2023-07-26T01:51:18.238775Z 0 [System] [MY-010116] [Server] /usr/sbin/mysqld (mysqld 8.0.32-24.2) starting as process 6129
2023-07-26T01:51:18.240915Z 0 [Warning] [MY-013242] [Server] --character-set-server: 'utf8' is currently an alias for the character set UTF8MB3, but will be an alias for UTF8MB4 in a future release. Please consider using UTF8MB4 in order to be unambiguous.
2023-07-26T01:51:18.243886Z 0 [Warning] [MY-010068] [Server] CA certificate ca.pem is self signed.
2023-07-26T01:51:18.243929Z 0 [System] [MY-013602] [Server] Channel mysql_main configured to support TLS. Encrypted connections are now supported for this channel.
2023-07-26T01:51:18.249172Z 0 [Warning] [MY-010075] [Server] No existing UUID has been found, so we assume that this is the first time that this server has been started. Generating a new UUID: e9aa301e-2b56-11ee-a47e-000c2948ee39.
2023-07-26T01:51:18.254102Z 1 [System] [MY-013576] [InnoDB] InnoDB initialization has started.
2023-07-26T01:51:18.446220Z 1 [System] [MY-013577] [InnoDB] InnoDB initialization has ended.
2023-07-26T01:51:18.461620Z 1 [System] [MY-011090] [Server] Data dictionary upgrading from version '80021' to '80023'.
2023-07-26T01:51:20.020760Z 1 [System] [MY-013413] [Server] Data dictionary upgrade from version '80021' to '80023' completed.
2023-07-26T01:51:20.288653Z 1 [Note] [MY-000000] [WSREP] wsrep_init_schema_and_SR (nil)
2023-07-26T01:51:22.618990Z 4 [System] [MY-013381] [Server] Server upgrade from '80021' to '80032' started.
2023-07-26T01:51:27.913366Z 4 [System] [MY-013381] [Server] Server upgrade from '80021' to '80032' completed.
2023-07-26T01:51:27.991646Z 0 [System] [MY-010229] [Server] Starting XA crash recovery...
2023-07-26T01:51:28.163501Z 0 [System] [MY-010232] [Server] XA crash recovery finished.
2023-07-26T01:51:28.220564Z 0 [Warning] [MY-010068] [Server] CA certificate ca.pem is self signed.
2023-07-26T01:51:28.220603Z 0 [System] [MY-013602] [Server] Channel mysql_main configured to support TLS. Encrypted connections are now supported for this channel.
2023-07-26T01:51:28.221965Z 0 [Warning] [MY-011810] [Server] Insecure configuration for --pid-file: Location '/tmp' in the path is accessible to all OS users. Consider choosing a different directory.
报错日志：
2023-07-26T01:51:28.224149Z 0 [ERROR] [MY-000067] [Server] unknown variable 'cert.pem;socket.ssl_ca=ca.pem"'.
2023-07-26T01:51:28.224217Z 0 [ERROR] [MY-010119] [Server] Aborting
2023-07-26T01:51:30.216961Z 0 [System] [MY-010910] [Server] /usr/sbin/mysqld: Shutdown complete (mysqld 8.0.32-24.2) Percona XtraDB Cluster (GPL), Release rel24, Revision 2119e75, WSREP version 26.1.4.3.
可见报错的是配置文件错误！原因是多了一个换行符的低级错误，修改后即可。
之后正确的做法是将node1也升级为最新版本即可。
