Deployment error: The limit of 5 diagnostic settings was reached

[brooke-hamilton]

Problem

If you have deployed and deleted Mission Landing Zone in the same subscription multiple times, you may eventually encounter this error (as viewed from the Deployments tab of the Azure portal):

{
    "status": "Failed",
    "error": {
        "code": "Conflict",
        "message": "The limit of 5 diagnostic settings was reached. To create new setting 'log-hub-sub-activity-to-<your prefix>-laws', delete an existing one."
    }
}

This is what the error looks like from the Azure CLI:

{"status":"Failed","error":{"code":"DeploymentFailed","message":"At least one resource deployment operation failed. Please list deployment operations for details. Please see https://aka.ms/DeployOperations for usage details.","details":[{"code":"Conflict","message":"{\r\n  \"status\": \"Failed\",\r\n  \"error\": {\r\n    \"code\": \"ResourceDeploymentFailure\",\r\n    \"message\": \"The resource operation completed with terminal provisioning state 'Failed'.\",\r\n    \"details\": [\r\n      {\r\n        \"code\": \"DeploymentFailed\",\r\n        \"message\": \"At least one resource deployment operation failed. Please list deployment operations for details. Please see https://aka.ms/DeployOperations for usage details.\",\r\n        \"details\": [\r\n          {\r\n            \"code\": \"Conflict\",\r\n            \"message\": \"{\\r\\n  \\\"code\\\": \\\"Conflict\\\",\\r\\n  \\\"message\\\": \\\"The limit of 5 diagnostic settings was reached. To create new setting 'log-hub-sub-activity-to-<your prefix>-laws', delete an existing one.\\\"\\r\\n}\"\r\n          }\r\n        ]\r\n      }\r\n    ]\r\n  }\r\n}"}]}}

Cause

Mission Landing Zone includes a diagnostic setting that directs the Azure activity log to the Log Analytics Workspace. The diagnostic setting is deployed at the subscription level, so if you delete all the resource groups for Mission Landing Zone, the diagnostic setting is left in your subscription even though it no longer points to a valid Log Analytics workspace.

Azure has a limit of five diagnostics settings at the subscription level, so if you have deployed and deleted Mission Landing Zone five times (without deleting the diagnostic settings), you will encounter this error the next time you deploy.

Solution

The solution is to delete unused diagnostic settings from the subscription. They can be deleted from the Azure Portal or using shell commands.

From the Azure Portal, choose the subscription blade, then Activity log in the left panel. At the top of the Activity log screen click the Diagnostics settings button. From there you can click the Edit setting link and delete the diagnostic setting.

Related Azure CLI examples are below:

# View diagnostic settings in the current subscription
az monitor diagnostic-settings subscription list --query value[] --output table

# Delete a diagnostic setting
az monitor diagnostic-settings subscription delete --name <diagnostic setting name>

More resources

Mission Landing Zone Cleanup Instructions (for Bicep)
https://docs.microsoft.com/en-us/azure/azure-monitor/essentials/activity-log#send-to-log-analytics-workspace
https://docs.microsoft.com/en-us/azure/azure-monitor/essentials/diagnostic-settings