Sampling

Sampling in in Azure functions

[[Tests done running Function locally on Visual Studio]]

  "logging": {
    "applicationInsights": {
      "enablePerformanceCountersCollection": false,
      "samplingSettings": {
        "isEnabled": true,
        "evaluationInterval": "00:00:10",
        "maxTelemetryItemsPerSecond": 2,
        "samplingPercentageDecreaseTimeout": "00:00:05",
        "samplingPercentageIncreaseTimeout": "00:00:05",
        "includedTypes": "Request"
      }
    }
  }

Important points:

• maxTelemetryItemsPerSecond : the maximum number of Requests sent to Application Insights service when sampling is active. (see below)
• samplingPercentageDecreaseTimeout and samplingPercentageIncreaseTimeout should be set to a low value, like 5 seconds. The default, 2 and 15 minutes, are too high. Low values allow the sampling algorithm to activate faster.
• if you activate Request exclusion i.e. “excludedTypes”: “Request” the sampling will not work. This is because all activities in Azure Functions are requests.
• “includedTypes”: “Request” is not strictly required because it’s the default. However, a more declarative config is better IMHO.
• disable performance counters if not really required –> “enablePerformanceCountersCollection”: false
• it’s possible to fix a max and min sampling level with options maxSamplingPercentage and minSamplingPercentage
• when running Functions on local emulator, it shows the application insights setup running values in the logs before starting the functions. This is usefull to check the real values used.

Sampling in Asp.Net - .NET Framework

• Got to: App Service –> Kudu –> Debug console –> /site/wwwroot/
• Edit ApplicationInsights.config
• Add / edit the following section:

<!-- 4% sample fixed rate with a max of 5 items (i.e. requests) per seconds -->
<Add Type="Microsoft.ApplicationInsights.WindowsServer.TelemetryChannel.AdaptiveSamplingTelemetryProcessor, Microsoft.AI.ServerTelemetryChannel">
  <MaxTelemetryItemsPerSecond>5</MaxTelemetryItemsPerSecond>
  <InitialSamplingPercentage>4</InitialSamplingPercentage>
  <MinSamplingPercentage>4</MinSamplingPercentage>
  <MaxSamplingPercentage>4</MaxSamplingPercentage>
</Add>

• Save and restart the app service

Availability - web monitoring

Standard (preview) tests

az monitor app-insights web-test list
az monitor app-insights web-test list --output table
az monitor app-insights web-test show --resource-group Monitoring --name httpscheck-xxxxx-httpmonitoring
az monitor app-insights web-test update --resource-group Monitoring --name httpscheck-xxxxx-httpmonitoring --timeout=10