How can we write alert rule comparing with the previous value for the prometheus alert rule

Question

I am trying to setup an alert rule for elastic search number of nodes. If the number is less than the previous number , then i need an alert. I don't want to hard code the value. Since number of nodes are vary for each cluster.

I am searching but couldn't able to find the answer, may be my search was wrong.

Answer 1

To alert this case, you can use

metric < metric offset 1m

Which will alert each time the value decrease in 1m. But be aware that resolve will be false here.