When a MySQL server is not reachable/available for any reason, Orchestrator may try anyway to run a show global status like 'Uptime' but it gets a Connection Refused error.

On a large environment this can generate a lot of log entries and more time spent by Orchestrator trying to establish the connection.

Example:

[...] ERROR ReadTopologyInstance(hostname:3306) show global status like 'Uptime': dial tcp hostname:3306: connect: connection refused

Suggested fix:

The ReadTopologyInstanceBufferable function does that. A suggested fix could be using the go.Ping() to check if the db is actually connected to first.

After db, err := db.OpenDiscovery(instanceKey.Hostname,instanceKey.Port)

https://github.com/percona/orchestrator/blob/master/go/inst/instance_dao.go#L382