Azure Application Insights - How to create an alert based on comparison between metrics?

Question

I am trying to create an alert based on comparison between few metrics for long running calculations.

Upon competition of batch (which varies in length) I am emitting 2 custom metric: DocsParsedTotal and DocsParsedSuccessful (both values are integers).

I can see those metrics with following query:

customMetrics 
| where timestamp >= ago(60m) 
| where name == "DocsParsedTotal" or name == "DocsParsedSuccessful"

Is there an option to extend metrics with sum(DocsParsedSuccessful) / sum(DocsParsedTotal) and create alert based on it?

I can also emit a metric for Ratio (per batch) but since my batches varies in length avg() it wont be precise.

Answer 1

It would be better if you can attach an screenshot of the query result in Application Insights -> logs as per the code in your post, like the screenshot in Step 1 of my answer.

And here is an example you can follow, but the data source may be different with yours.

1.The data source in my test:

2.Then you can use the query below:

customMetrics 
| where timestamp >= ago(1d) 
| where name == "DocsParsedTotal" or name == "DocsParsedSuccessful"
| summarize a2=sumif(value,name=="DocsParsedTotal"),a1=sumif(value,name == "DocsParsedSuccessful")
| extend s1 = iff(a1/a2>2,"alert","not alert")
| where s1 =="alert"

Note of the query:

for this line of code extend s1 = iff(a1/a2>2,"alert","not alert"), if a1/a2>2(you can set it to any value instead of 2 as per your need) is true, then by using where s1 =="alert", there should be always 1 result returned. Otherwise, 0 result returned.

3.Next, click the "New alert rule":

4.Then in the "Create rule" page, please follow the steps in screenshot below:

Please let me know if you still have more issues.