Back-end health and diagnostic logs for Application Gateway

By using Azure Application Gateway, you can monitor resources in the following ways:

  • Back-end health: Application Gateway provides the capability to monitor the health of the servers in the back-end pools through the Azure portal and through PowerShell. You can also find the health of the back-end pools through the performance diagnostic logs.

  • Logs: Logs allow for performance, access, and other data to be saved or consumed from a resource for monitoring purposes.

  • Metrics: Application Gateway has several metrics which help you verify that your system is performing as expected.

Note

This article has been updated to use the new Azure PowerShell Az module. You can still use the AzureRM module, which will continue to receive bug fixes until at least December 2020. To learn more about the new Az module and AzureRM compatibility, see Introducing the new Azure PowerShell Az module. For Az module installation instructions, see Install Azure PowerShell.

Back-end health

Application Gateway provides the capability to monitor the health of individual members of the back-end pools through the portal, PowerShell, and the command-line interface (CLI). You can also find an aggregated health summary of back-end pools through the performance diagnostic logs.

The back-end health report reflects the output of the Application Gateway health probe to the back-end instances. When probing is successful and the back end can receive traffic, it's considered healthy. Otherwise, it's considered unhealthy.

Important

If there is a network security group (NSG) on an Application Gateway subnet, open port ranges 65503-65534 on the Application Gateway subnet for inbound traffic. This port range is required for Azure infrastructure communication. They are protected (locked down) by Azure certificates. Without proper certificates, external entities, including the customers of those gateways, will not be able to initiate any changes on those endpoints.

View back-end health through the portal

In the portal, back-end health is provided automatically. In an existing application gateway, select Monitoring > Backend health.

Each member in the back-end pool is listed on this page (whether it's a NIC, IP, or FQDN). Back-end pool name, port, back-end HTTP settings name, and health status are shown. Valid values for health status are Healthy, Unhealthy, and Unknown.

Note

If you see a back-end health status of Unknown, ensure that access to the back end is not blocked by an NSG rule, a user-defined route (UDR), or a custom DNS in the virtual network.

Back-end health

View back-end health through PowerShell

The following PowerShell code shows how to view back-end health by using the Get-AzApplicationGatewayBackendHealth cmdlet:

Get-AzApplicationGatewayBackendHealth -Name ApplicationGateway1 -ResourceGroupName Contoso

View back-end health through Azure CLI

az network application-gateway show-backend-health --resource-group AdatumAppGatewayRG --name AdatumAppGateway

Results

The following snippet shows an example of the response:

{
"BackendAddressPool": {
    "Id": "/subscriptions/00000000-0000-0000-000000000000/resourceGroups/ContosoRG/providers/Microsoft.Network/applicationGateways/applicationGateway1/backendAddressPools/appGatewayBackendPool"
},
"BackendHttpSettingsCollection": [
    {
    "BackendHttpSettings": {
        "Id": "/00000000-0000-0000-000000000000/resourceGroups/ContosoRG/providers/Microsoft.Network/applicationGateways/applicationGateway1/backendHttpSettingsCollection/appGatewayBackendHttpSettings"
    },
    "Servers": [
        {
        "Address": "hostname.westus.cloudapp.azure.com",
        "Health": "Healthy"
        },
        {
        "Address": "hostname.westus.cloudapp.azure.com",
        "Health": "Healthy"
        }
    ]
    }
]
}

Diagnostic logs

You can use different types of logs in Azure to manage and troubleshoot application gateways. You can access some of these logs through the portal. All logs can be extracted from Azure Blob storage and viewed in different tools, such as Azure Monitor logs, Excel, and Power BI. You can learn more about the different types of logs from the following list:

  • Activity log: You can use Azure activity logs (formerly known as operational logs and audit logs) to view all operations that are submitted to your Azure subscription, and their status. Activity log entries are collected by default, and you can view them in the Azure portal.
  • Access log: You can use this log to view Application Gateway access patterns and analyze important information. This includes the caller's IP, requested URL, response latency, return code, and bytes in and out. An access log is collected every 300 seconds. This log contains one record per instance of Application Gateway. The Application Gateway instance is identified by the instanceId property.
  • Performance log: You can use this log to view how Application Gateway instances are performing. This log captures performance information for each instance, including total requests served, throughput in bytes, total requests served, failed request count, and healthy and unhealthy back-end instance count. A performance log is collected every 60 seconds. The Performance log is available only for the v1 SKU. For the v2 SKU, use Metrics for performance data.
  • Firewall log: You can use this log to view the requests that are logged through either detection or prevention mode of an application gateway that is configured with the web application firewall.

Note

Logs are available only for resources deployed in the Azure Resource Manager deployment model. You cannot use logs for resources in the classic deployment model. For a better understanding of the two models, see the Understanding Resource Manager deployment and classic deployment article.

You have three options for storing your logs:

  • Storage account: Storage accounts are best used for logs when logs are stored for a longer duration and reviewed when needed.
  • Event hubs: Event hubs are a great option for integrating with other security information and event management (SIEM) tools to get alerts on your resources.
  • Azure Monitor logs: Azure Monitor logs is best used for general real-time monitoring of your application or looking at trends.

Enable logging through PowerShell

Activity logging is automatically enabled for every Resource Manager resource. You must enable access and performance logging to start collecting the data available through those logs. To enable logging, use the following steps:

  1. Note your storage account's resource ID, where the log data is stored. This value is of the form: /subscriptions/<subscriptionId>/resourceGroups/<resource group name>/providers/Microsoft.Storage/storageAccounts/<storage account name>. You can use any storage account in your subscription. You can use the Azure portal to find this information.

    Portal: resource ID for storage account

  2. Note your application gateway's resource ID for which logging is enabled. This value is of the form: /subscriptions/<subscriptionId>/resourceGroups/<resource group name>/providers/Microsoft.Network/applicationGateways/<application gateway name>. You can use the portal to find this information.

    Portal: resource ID for application gateway

  3. Enable diagnostic logging by using the following PowerShell cmdlet:

    Set-AzDiagnosticSetting  -ResourceId /subscriptions/<subscriptionId>/resourceGroups/<resource group name>/providers/Microsoft.Network/applicationGateways/<application gateway name> -StorageAccountId /subscriptions/<subscriptionId>/resourceGroups/<resource group name>/providers/Microsoft.Storage/storageAccounts/<storage account name> -Enabled $true     
    

Tip

Activity logs do not require a separate storage account. The use of storage for access and performance logging incurs service charges.

Enable logging through the Azure portal

  1. In the Azure portal, find your resource and select Diagnostic settings.

    For Application Gateway, three logs are available:

    • Access log
    • Performance log
    • Firewall log
  2. To start collecting data, select Turn on diagnostics.

    Turning on diagnostics

  3. The Diagnostics settings page provides the settings for the diagnostic logs. In this example, Log Analytics stores the logs. You can also use event hubs and a storage account to save the diagnostic logs.

    Starting the configuration process

  4. Type a name for the settings, confirm the settings, and select Save.

Activity log

Azure generates the activity log by default. The logs are preserved for 90 days in the Azure event logs store. Learn more about these logs by reading the View events and activity log article.

Access log

The access log is generated only if you've enabled it on each Application Gateway instance, as detailed in the preceding steps. The data is stored in the storage account that you specified when you enabled the logging. Each access of Application Gateway is logged in JSON format, as shown in the following example for v1:

Value Description
instanceId Application Gateway instance that served the request.
clientIP Originating IP for the request.
clientPort Originating port for the request.
httpMethod HTTP method used by the request.
requestUri URI of the received request.
RequestQuery Server-Routed: Back-end pool instance that was sent the request.
X-AzureApplicationGateway-LOG-ID: Correlation ID used for the request. It can be used to troubleshoot traffic issues on the back-end servers.
SERVER-STATUS: HTTP response code that Application Gateway received from the back end.
UserAgent User agent from the HTTP request header.
httpStatus HTTP status code returned to the client from Application Gateway.
httpVersion HTTP version of the request.
receivedBytes Size of packet received, in bytes.
sentBytes Size of packet sent, in bytes.
timeTaken Length of time (in milliseconds) that it takes for a request to be processed and its response to be sent. This is calculated as the interval from the time when Application Gateway receives the first byte of an HTTP request to the time when the response send operation finishes. It's important to note that the Time-Taken field usually includes the time that the request and response packets are traveling over the network.
sslEnabled Whether communication to the back-end pools used SSL. Valid values are on and off.
host The hostname with which the request has been sent to the backend server. If backend hostname is being overridden, this name will reflect that.
originalHost The hostname with which the request was received by the Application Gateway from the client.
{
    "resourceId": "/SUBSCRIPTIONS/{subscriptionId}/RESOURCEGROUPS/PEERINGTEST/PROVIDERS/MICROSOFT.NETWORK/APPLICATIONGATEWAYS/{applicationGatewayName}",
    "operationName": "ApplicationGatewayAccess",
    "time": "2017-04-26T19:27:38Z",
    "category": "ApplicationGatewayAccessLog",
    "properties": {
        "instanceId": "ApplicationGatewayRole_IN_0",
        "clientIP": "191.96.249.97",
        "clientPort": 46886,
        "httpMethod": "GET",
        "requestUri": "/phpmyadmin/scripts/setup.php",
        "requestQuery": "X-AzureApplicationGateway-CACHE-HIT=0&SERVER-ROUTED=10.4.0.4&X-AzureApplicationGateway-LOG-ID=874f1f0f-6807-41c9-b7bc-f3cfa74aa0b1&SERVER-STATUS=404",
        "userAgent": "-",
        "httpStatus": 404,
        "httpVersion": "HTTP/1.0",
        "receivedBytes": 65,
        "sentBytes": 553,
        "timeTaken": 205,
        "sslEnabled": "off",
        "host": "www.contoso.com",
        "originalHost": "www.contoso.com"
    }
}

For Application Gateway and WAF v2, the logs show a little more information:

Value Description
instanceId Application Gateway instance that served the request.
clientIP Originating IP for the request.
clientPort Originating port for the request.
httpMethod HTTP method used by the request.
requestUri URI of the received request.
UserAgent User agent from the HTTP request header.
httpStatus HTTP status code returned to the client from Application Gateway.
httpVersion HTTP version of the request.
receivedBytes Size of packet received, in bytes.
sentBytes Size of packet sent, in bytes.
timeTaken Length of time (in seconds) that it takes for a request to be processed and its response to be sent. This is calculated as the interval from the time when Application Gateway receives the first byte of an HTTP request to the time when the response send operation finishes. It's important to note that the Time-Taken field usually includes the time that the request and response packets are traveling over the network.
sslEnabled Whether communication to the back-end pools used SSL. Valid values are on and off.
sslCipher Cipher suite being used for SSL communication (if SSL is enabled).
sslProtocol SSL/TLS protocol being used (if SSL is enabled).
serverRouted The backend server that application gateway routes the request to.
serverStatus HTTP status code of the backend server.
serverResponseLatency Latency of the response from the backend server.
host Address listed in the host header of the request.
{
    "resourceId": "/SUBSCRIPTIONS/{subscriptionId}/RESOURCEGROUPS/PEERINGTEST/PROVIDERS/MICROSOFT.NETWORK/APPLICATIONGATEWAYS/{applicationGatewayName}",
    "operationName": "ApplicationGatewayAccess",
    "time": "2017-04-26T19:27:38Z",
    "category": "ApplicationGatewayAccessLog",
    "properties": {
        "instanceId": "appgw_1",
        "clientIP": "191.96.249.97",
        "clientPort": 46886,
        "httpMethod": "GET",
        "requestUri": "/phpmyadmin/scripts/setup.php",
        "userAgent": "-",
        "httpStatus": 404,
        "httpVersion": "HTTP/1.0",
        "receivedBytes": 65,
        "sentBytes": 553,
        "timeTaken": 205,
        "sslEnabled": "off",
        "sslCipher": "",
        "sslProtocol": "",
        "serverRouted": "104.41.114.59:80",
        "serverStatus": "200",
        "serverResponseLatency": "0.023",
        "host": "www.contoso.com",
    }
}

Performance log

The performance log is generated only if you have enabled it on each Application Gateway instance, as detailed in the preceding steps. The data is stored in the storage account that you specified when you enabled the logging. The performance log data is generated in 1-minute intervals. It is available only for the v1 SKU. For the v2 SKU, use Metrics for performance data. The following data is logged:

Value Description
instanceId Application Gateway instance for which performance data is being generated. For a multiple-instance application gateway, there is one row per instance.
healthyHostCount Number of healthy hosts in the back-end pool.
unHealthyHostCount Number of unhealthy hosts in the back-end pool.
requestCount Number of requests served.
latency Average latency (in milliseconds) of requests from the instance to the back end that serves the requests.
failedRequestCount Number of failed requests.
throughput Average throughput since the last log, measured in bytes per second.
{
    "resourceId": "/SUBSCRIPTIONS/{subscriptionId}/RESOURCEGROUPS/{resourceGroupName}/PROVIDERS/MICROSOFT.NETWORK/APPLICATIONGATEWAYS/{applicationGatewayName}",
    "operationName": "ApplicationGatewayPerformance",
    "time": "2016-04-09T00:00:00Z",
    "category": "ApplicationGatewayPerformanceLog",
    "properties":
    {
        "instanceId":"ApplicationGatewayRole_IN_1",
        "healthyHostCount":"4",
        "unHealthyHostCount":"0",
        "requestCount":"185",
        "latency":"0",
        "failedRequestCount":"0",
        "throughput":"119427"
    }
}

Note

Latency is calculated from the time when the first byte of the HTTP request is received to the time when the last byte of the HTTP response is sent. It's the sum of the Application Gateway processing time plus the network cost to the back end, plus the time that the back end takes to process the request.

Firewall log

The firewall log is generated only if you have enabled it for each application gateway, as detailed in the preceding steps. This log also requires that the web application firewall is configured on an application gateway. The data is stored in the storage account that you specified when you enabled the logging. The following data is logged:

Value Description
instanceId Application Gateway instance for which firewall data is being generated. For a multiple-instance application gateway, there is one row per instance.
clientIp Originating IP for the request.
clientPort Originating port for the request.
requestUri URL of the received request.
ruleSetType Rule set type. The available value is OWASP.
ruleSetVersion Rule set version used. Available values are 2.2.9 and 3.0.
ruleId Rule ID of the triggering event.
message User-friendly message for the triggering event. More details are provided in the details section.
action Action taken on the request. Available values are Blocked and Allowed.
site Site for which the log was generated. Currently, only Global is listed because rules are global.
details Details of the triggering event.
details.message Description of the rule.
details.data Specific data found in request that matched the rule.
details.file Configuration file that contained the rule.
details.line Line number in the configuration file that triggered the event.
hostname Hostname or IP address of the Application Gateway.
transactionId Unique ID for a given transaction which helps group multiple rule violations that occurred within the same request.
{
  "resourceId": "/SUBSCRIPTIONS/{subscriptionId}/RESOURCEGROUPS/{resourceGroupName}/PROVIDERS/MICROSOFT.NETWORK/APPLICATIONGATEWAYS/{applicationGatewayName}",
  "operationName": "ApplicationGatewayFirewall",
  "time": "2017-03-20T15:52:09.1494499Z",
  "category": "ApplicationGatewayFirewallLog",
  "properties": {
    "instanceId": "ApplicationGatewayRole_IN_0",
    "clientIp": "104.210.252.3",
    "clientPort": "4835",
    "requestUri": "/?a=%3Cscript%3Ealert(%22Hello%22);%3C/script%3E",
    "ruleSetType": "OWASP",
    "ruleSetVersion": "3.0",
    "ruleId": "941320",
    "message": "Possible XSS Attack Detected - HTML Tag Handler",
    "action": "Blocked",
    "site": "Global",
    "details": {
      "message": "Warning. Pattern match \"<(a|abbr|acronym|address|applet|area|audioscope|b|base|basefront|bdo|bgsound|big|blackface|blink|blockquote|body|bq|br|button|caption|center|cite|code|col|colgroup|comment|dd|del|dfn|dir|div|dl|dt|em|embed|fieldset|fn|font|form|frame|frameset|h1|head|h ...\" at ARGS:a.",
      "data": "Matched Data: <script> found within ARGS:a: <script>alert(\\x22hello\\x22);</script>",
      "file": "rules/REQUEST-941-APPLICATION-ATTACK-XSS.conf",
      "line": "865"
    }
    "hostname": "40.90.218.100", 
    "transactionId": "AYAcUqAcAcAcAcAcASAcAcAc"
  }
} 

View and analyze the activity log

You can view and analyze activity log data by using any of the following methods:

  • Azure tools: Retrieve information from the activity log through Azure PowerShell, the Azure CLI, the Azure REST API, or the Azure portal. Step-by-step instructions for each method are detailed in the Activity operations with Resource Manager article.
  • Power BI: If you don't already have a Power BI account, you can try it for free. By using the Power BI template apps, you can analyze your data.

View and analyze the access, performance, and firewall logs

Azure Monitor logs can collect the counter and event log files from your Blob storage account. It includes visualizations and powerful search capabilities to analyze your logs.

You can also connect to your storage account and retrieve the JSON log entries for access and performance logs. After you download the JSON files, you can convert them to CSV and view them in Excel, Power BI, or any other data-visualization tool.

Tip

If you are familiar with Visual Studio and basic concepts of changing values for constants and variables in C#, you can use the log converter tools available from GitHub.

Analyzing Access logs through GoAccess

We have published a Resource Manager template that installs and runs the popular GoAccess log analyzer for Application Gateway Access Logs. GoAccess provides valuable HTTP traffic statistics such as Unique Visitors, Requested Files, Hosts, Operating Systems, Browsers, HTTP Status codes and more. For more details, please see the Readme file in the Resource Manager template folder in GitHub.

Next steps