About Azure Metrics Requests and App Service HTTP Logs

Question

I want to issue an alert when a certain number of requests are exceeded.

To check the number of requests, I ran the following queries in AppService respectively.

let start=datetime("2022-05-26 00:00:00") -9h;
let end = datetime("2022-05-27 14:30:00") -9h;
AppServiceHTTPLogs
| where TimeGenerated between (start .. end)
| summarize count() by bin(TimeGenerated, 1h)

let metricName ="Requests";
let start=datetime("2022-05-26 00:00:00") -9h;
let end = datetime("2022-05-27 14:30:00") -9h;
AzureMetrics
| where TimeGenerated between (start .. end)
| where MetricName==metricName
| summarize sum(total) by bin(TimeGenerated, 1h)

Then

2022/5/26 0:00
AppServiceHTTPLogs：3115
AzureMetrics ：3045

2022/5/26 1:00
AppServiceHTTPLogs：2961
AzureMetrics ：2928

：

The numbers did not match each hour.

If you look at the description of Requests in Azure Metrics
"The total number of requests, regardless of the resulting HTTP status code."
I think it matches the number of lines output to AppServiceHTTPLogs, is that wrong?

Which is more appropriate, AppServiceHTTPLogs output rows or AzureMetrics-Requests total, when monitoring over-requests?

Answer 1

Hi @真 川崎 ,

After doing some tests with a test AzureWebApp deployed, I noticed the following:

1. The Requests in AzureMetric stores the Total Requests with aggregation also in place. Therefore, a single record here might correspond to multiple requests. In the screenshot below, the record count is 3 but Total sums up to 4. (Note the TimeGrain columns as PT1M which means that the metrics are aggregated every 1 minute).

2. For the same AppService over the same time range, the AppServiceHTTPLogs has 4 records matching the numbers.

Therefore, for your requirement, you can use the count of record as returned from AppServiceHTTPLogs (or even the AzureMetrics/Requests, but that will require the use of sum over Total)

Please let me know if you have any questions.

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