Function Apps Troubleshooting

Find Linked App Insights / Log Analytics

Preferred: Use Azure Resource Graph

A single ARG query returns the App Insights name, instrumentation key, connection string, and Log Analytics workspace for a given function app:

az graph query -q "
resources | where type =~ 'microsoft.web/sites' and name == '<func-app-name>'
| project funcName=name, rg=resourceGroup
| join kind=inner (resources | where type =~ 'microsoft.insights/components' | project appiName=name, rg=resourceGroup, instrumentationKey=properties.InstrumentationKey, connectionString=properties.ConnectionString, workspaceId=properties.WorkspaceResourceId) on rg
| project funcName, appiName, instrumentationKey, connectionString, workspaceId
" -o json

💡 Tip: This join matches by resource group. If App Insights is in a different resource group, use the CLI fallback below.

Fallback: CLI Commands

#### Step 1: Get the App Insights connection string from app settings

az functionapp config appsettings list \
  --name <func-app-name> -g <rg-name> \
  --query "[?name=='APPLICATIONINSIGHTS_CONNECTION_STRING' || name=='APPINSIGHTS_INSTRUMENTATIONKEY']"

#### Step 2: Find the App Insights resource by instrumentation key

az monitor app-insights component show \
  --query "[?instrumentationKey=='<key>'] | [0].{name:name, rg:resourceGroup, workspaceId:workspaceResourceId}"

#### Step 3: Find the Log Analytics workspace

az monitor app-insights component show --app <appinsights-name> -g <rg-name> \
  --query "workspaceResourceId" -o tsv

Confirm logs are flowing

Query App Insights traces table to verify the function app is sending telemetry:

az monitor app-insights query --apps <appinsights-name> -g <rg-name> \
  --analytics-query "traces | where operation_Name != '' | take 1 | project timestamp, operation_Name, message"

For FunctionAppLogs (available in Log Analytics only, not App Insights), query the workspace directly:

az monitor log-analytics query -w <workspace-guid> \
  --analytics-query "FunctionAppLogs | where _ResourceId contains '<func-app-name>' | take 5 | project TimeGenerated, FunctionName, Message, Level"

⚠️ Classic App Insights: Some function apps use classic App Insights without a linked Log Analytics workspace (workspaceId is null). In this case, FunctionAppLogs is not available — use the traces, requests, and exceptions tables via az monitor app-insights query instead. As a last resort, az webapp log tail --name <func-app-name> -g <rg-name> can stream live logs directly.

If results are returned, logs are flowing. If empty, verify the APPLICATIONINSIGHTS_CONNECTION_STRING app setting matches this App Insights instance.

⚠️ Always prefer querying App Insights or Log Analytics for function app logs. az webapp log tail can stream live logs directly but App Insights provides richer data, historical queries, and correlation across requests.

💡 Tip: App Insights logs can be delayed by a few minutes. If you don't see recent data, wait 3-5 minutes and query again.

Check Recent Deployments

Correlate issues with recent deployments by listing deployment history:

az rest --method get \
  --uri "/subscriptions/<subscription-id>/resourceGroups/<rg-name>/providers/Microsoft.Web/sites/<func-app-name>/deployments?api-version=2023-12-01"

Compare deployment timestamps against when errors started appearing in App Insights to identify if a deployment caused the issue.