I'm experimenting with Galera in my Rocky openstack-ansible dev cluster, and I'm finding that the default haproxy config values don't seem to work. Finding the correct values is a lot of work. For example, I spent this morning experimenting with different values for "timeout client" in /etc/haproxy/haproxy.cfg. The default is 1m, and with the default set I see this error in /var/log/nova/nova-scheduler.log on the controllers:
2020-01-17 13:54:26.059 443358 ERROR oslo_db.sqlalchemy.engines DBConnectionError: (pymysql.err.OperationalError) (2013, 'Lost connection to MySQL server during query') [SQL: u'SELECT 1'] (Background on this error at: http://sqlalche.me/e/e3q8)
There are several timeout values in /etc/haproxy/haproxy.cfg. These are the values we started with:
stats timeout 30s timeout http-request 10s timeout queue 1m timeout connect 10s timeout client 1m timeout server 1m timeout check 10s
At first I changed them all to 30m. This stopped the "Lost connection" error in nova-scheduler.log. Then, one at a time, I changed them back to the default. When I got to "timeout client" I found that setting it back to 1m caused the errors to start again. I changed it back and forth and found that 4 minutes causes errors, and 6m stops them, so I left it at 6m.
These are my active variables:
root@us01odc-dev2-ctrl1:/etc/mysql# mysql -e 'show variables;'|grep timeout connect_timeout 20 deadlock_timeout_long 50000000 deadlock_timeout_short 10000 delayed_insert_timeout 300 idle_readonly_transaction_timeout 0 idle_transaction_timeout 0 idle_write_transaction_timeout 0 innodb_flush_log_at_timeout 1 innodb_lock_wait_timeout 50 innodb_rollback_on_timeout OFF interactive_timeout 28800 lock_wait_timeout 86400 net_read_timeout 30 net_write_timeout 60 rpl_semi_sync_master_timeout 10000 rpl_semi_sync_slave_kill_conn_timeout 5 slave_net_timeout 60 thread_pool_idle_timeout 60 wait_timeout 3600
So it looks like the value of "timeout client" in haproxy.cfg needs to match or exceed the value of "wait_timeout" in mysql. Also in nova.conf I see "#connection_recycle_time = 3600" - I need to experiment to see how that value interacts with the timeouts in the other config files.
Is this the best way to find the correct config values? It seems like there should be a document that talks about these timeouts and how to set them (or maybe more generally how the different timeout settings in the various config files interact). Does that document exist? If not, maybe I could write one, since I have to figure out the correct values anyway.