Implement read_only in mysqlmon to allow (a/semi-sync) multimaster setups with slaves

Hi,

I am working with a setup with 2 asynchronous masters. Each master has a slave. The inactive master has read_only enabled. It is an active/passive setup for the masters but active/active setup for the 2 slaves. The passive master shouldn't fall behind the master but we want to check replication lag on the slaves. This is not possible in the mmmon monitor.

I think the best solution would be to merge the functionality of mmmon into mysqlmon:
When I currently run the 4 servers in 1 mysqlmon, all 4 servers become slave. If there are 2 root nodes (or: a circular replication setup), initially both of the nodes should become master. Next, we check if any of them have read_only enabled. If they do, the master state should be removed from (or not added to) that node. This feature would make mmmon obsolete.

Thanks,
Michaël