PMM alarm monitoring MySQL use nails

Open PMM Serverpage, as shown in FIG point into Alerting -> Notification channels

Nails input information, and Save Test

The test results, no problem

How to use the alarm granafa do it? Casually points to open a monitored item, I'm here for galera cluster sizeexample.

Click Alertas shown in Figure

Emphasis Conditions, here is an expression I set

avg() query(C,5m,now) 3 - 3

AVG () Meaning: the average period of the panel
probably means that the average over five minutes to be in the 3-3 range. Otherwise an alarm.

This is the warning notes

The effect is as:

Common error

When prompted to add Alert template variables are not supported in alert queries
official reply:

https://github.com/grafana/grafana/issues/9334
Template variables are not supported in alerting.
Template variables should be used for discovery and drill down. Not controlling alert rules

Approach:
copy this Dashboard of json, the inside of the variables are replaced by constants.

Examples are as follows:
the original

      "expr": "max_over_time(mysql_global_status_wsrep_cluster_size{instance=~\"$host\"}[$interval]) or\nmax_over_time(mysql_global_status_wsrep_cluster_size{instance=~\"$host\"}[5m])",

Changed

      "expr": "max_over_time(mysql_global_status_wsrep_cluster_size{instance=~\"pxc1\"}[1m]) 
or\nmax_over_time(mysql_global_status_wsrep_cluster_size{instance=~\"pxc1\"}[5m])",

And then re-added to the alarm.