Troubleshoot backend health issues in Azure Application Gateway (2022)

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Overview

By default, Azure Application Gateway probes backend servers to check their health status and to check whether they're ready to serve requests. Users can also create custom probes to mention the host name, the path to be probed, and the status codes to be accepted as Healthy. In each case, if the backend server doesn't respond successfully, Application Gateway marks the server as Unhealthy and stops forwarding requests to the server. After the server starts respondingsuccessfully, Application Gateway resumes forwarding the requests.

How to check backend health

To check the health of your backend pool, you can use theBackend Health page on the Azure portal. Or, you can use Azure PowerShell, CLI, or REST API.

The status retrieved by any of these methods can be any one of the following states:

  • Healthy
  • Unhealthy
  • Unknown

If the backend health status for a server is healthy, it means that Application Gateway will forward the requests to that server. But if the backend health for all the servers in a backend pool is unhealthy or unknown, you might encounter problems when you try to accessapplications. This article describes the symptoms, cause, and resolution for each of the errors shown.

Backend health status: Unhealthy

If the backend health status is Unhealthy, the portal view will resemble the following screenshot:

Troubleshoot backend health issues in Azure Application Gateway (1)

Or if you're using an Azure PowerShell, CLI, or Azure REST API query, you'll get a response that resembles the following example:

PS C:\Users\testuser\> Get-AzApplicationGatewayBackendHealth -Name "appgw1" -ResourceGroupName "rgOne"BackendAddressPools :{Microsoft.Azure.Commands.Network.Models.PSApplicationGatewayBackendHealthPool}BackendAddressPoolsText : [{ "BackendAddressPool": { "Id": "/subscriptions/536d30b8-665b-40fc-bd7e-68c65f816365/resourceGroups/rgOne/providers/Microsoft.Network/applicationGateways/appgw1/b ackendAddressPools/appGatewayBackendPool" }, "BackendHttpSettingsCollection": [ { "BackendHttpSettings": { "TrustedRootCertificates": [], "Id": "/subscriptions/536d30b8-665b-40fc-bd7e-68c65f816365/resourceGroups/rgOne/providers/Microsoft.Network/applicationGateways/appg w1/backendHttpSettingsCollection/appGatewayBackendHttpSettings" }, "Servers": [ { "Address": "10.0.0.5", "Health": "Healthy" }, { "Address": "10.0.0.6", "Health": "Unhealthy" } ] } ] } ]

After you receive an unhealthy backend server status for all the servers in a backend pool, requests aren't forwarded to the servers, and Application Gateway returns a "502 Bad Gateway" error to the requesting client. To troubleshoot this issue, check the Details column on the Backend Health tab.

The message displayed in the Details column provides more detailed insights about the issue, and based on those details, you can start troubleshooting the issue.

Note

The default probe request is sent in the format of <protocol>://127.0.0.1:<port>. For example, http://127.0.0.1:80 for an HTTP probe on port 80. Only HTTP status codes of 200 through 399 are considered healthy. The protocol and destination port are inherited from the HTTP settings. If you want Application Gateway to probe on a different protocol, host name, or path and to recognize a different status code as Healthy, configure a custom probe and associate it with the HTTP settings.

Error messages

Backend server timeout

Message: Time taken by the backend to respond to application gateway's health probe is more than the timeout threshold in the probe setting.

Cause: After Application Gateway sends an HTTP(S) probe request to thebackend server, it waits for a response from the backend server for a configured period. If the backend server doesn'trespond within the configured period (the timeout value), it's marked as Unhealthy until it starts responding within the configured timeout period again.

Resolution: Check why the backend server or application isn't responding within the configured timeout period, and also check the application dependencies. For example, check whether the database has any issues that might trigger a delay in response. If you're aware of the application's behavior and it should respond only after the timeout value, increase the timeout value from the custom probe settings. You must have a custom probe to change the timeout value. For information about how to configure a custom probe, see the documentation page.

To increase the timeout value, follow these steps:

  1. Access the backend server directly and check the time taken for the server to respond on that page. You can use any tool to access the backend server, including a browser using developer tools.
  2. After you've figured out the time taken for the application to respond, select the Health Probes tab, then select the probe that's associated with your HTTP settings.
  3. Enter any timeout value that's greater than the application response time, in seconds.
  4. Save the custom probe settings and check whether the backend health shows as Healthy now.

DNS resolution error

Message: Application Gateway could not create a probe for this backend. This usually happens when the FQDN of the backend has not been entered correctly.

Cause: If the backend pool is of type IP Address, FQDN or App Service, Application Gateway resolves to the IP address of the FQDN entered through DNS (custom or Azure default). The application gateway then tries to connect to the server on the TCP port mentioned in the HTTP settings. But if this message is displayed, it suggests that Application Gateway couldn't successfully resolve the IP address of the FQDN entered.

Resolution:

(Video) Microsoft Azure Application Gateway Deep Dive

  1. Verify that the FQDN entered in the backend pool is correct and that it's a public domain, then try to resolve it from your local machine.
  2. If you can resolve the IP address, there might be something wrong with the DNS configuration in the virtual network.
  3. Check whether the virtual network is configured with a custom DNS server. If it is, check the DNS server about why it can't resolve to the IP address of the specified FQDN.
  4. If you're using Azure default DNS, check with your domain name registrar about whether proper A record or CNAME record mapping has been completed.
  5. If the domain is private or internal, try to resolve it from a VM in the same virtual network. If you can resolve it, restart Application Gateway and check again. To restart Application Gateway, you need to stop and start by using the PowerShell commands described in these linked resources.

Updates to the DNS entries of the backend pool

Message: The backend health status could not be retrieved. This happens when an NSG/UDR/Firewall on the application gateway subnet is blocking traffic on ports 65503-65534 in case of v1 SKU, and ports 65200-65535 in case of the v2 SKU or if the FQDN configured in the backend pool could not be resolved to an IP address. To learn more visit - https://aka.ms/UnknownBackendHealth.

Cause: Application Gateway resolves the DNS entries for the backend pool at time of startup and doesn't update them dynamically while running.

Resolution:

Application Gateway must be restarted after any modification to the backend server DNS entries to begin to use the new IP addresses. This operation can be completed via Azure PowerShell or Azure CLI.

Azure PowerShell

# Get Azure Application Gateway$appgw=Get-AzApplicationGateway -Name <appgw_name> -ResourceGroupName <rg_name> # Stop the Azure Application GatewayStop-AzApplicationGateway -ApplicationGateway $appgw # Start the Azure Application GatewayStart-AzApplicationGateway -ApplicationGateway $appgw

Azure CLI

# Stop the Azure Application Gatewayaz network application-gateway stop -n <appgw_name> -g <rg_name># Start the Azure Application Gatewayaz network application-gateway start -n <appgw_name> -g <rg_name>

TCP connect error

Message: Application Gateway could not connect to the backend. Check that the backend responds on the port used for the probe. Also check whether any NSG/UDR/Firewall is blocking access to the Ip and port of this backend.

Cause: After the DNS resolution phase, Application Gateway tries to connect to the backend server on the TCP port that's configured in the HTTP settings. If Application Gateway can't establish a TCP session on the port specified, the probe is marked as Unhealthy with this message.

Solution: If you receive this error, follow these steps:

  1. Check whether you can connect to the backend server on the port mentioned in the HTTP settings by using a browser or PowerShell. For example, run the following command: Test-NetConnection -ComputerName www.bing.com -Port 443.

  2. If the port mentioned is not the desired port, enter the correct port number for Application Gateway to connect to the backend server.

  3. If you can't connect on the port from your local machine as well, then:

    a. Check the network security group (NSG) settings of the backend server's network adapter and subnet and whether inbound connections to the configured port are allowed. If they aren't, create a new rule to allow the connections. To learn how to create NSG rules, see the documentation page.

    b. Check whether the NSG settings of the Application Gateway subnet allow outbound public and private traffic, so that a connection can be made. Check the document page that's provided in step 3a to learn more about how to create NSG rules.

     $vnet = Get-AzVirtualNetwork -Name "vnetName" -ResourceGroupName "rgName" Get-AzVirtualNetworkSubnetConfig -Name appGwSubnet -VirtualNetwork $vnet

    c. Check the user-defined routes (UDR) settings of Application Gateway and the backend server's subnet for any routing anomalies. Make sure the UDR isn't directing the traffic away from the backend subnet. For example, check for routes to network virtual appliances or default routes being advertised to the Application Gateway subnet via Azure ExpressRoute and/or VPN.

    d. To check the effective routes and rules for a network adapter, you can use the following PowerShell commands:

     Get-AzEffectiveNetworkSecurityGroup -NetworkInterfaceName "nic1" -ResourceGroupName "testrg" Get-AzEffectiveRouteTable -NetworkInterfaceName "nic1" -ResourceGroupName "testrg"
  4. If you don't find any issues with NSG or UDR, check your backend server for application-related issues that are preventing clients from establishing a TCP session on the ports configured. A few things to check:

    a. Open a command prompt (Win+R -> cmd), enter netstat, and select Enter.

    b. Check whether the server is listening on the port that's configured. For example:

     Proto Local Address Foreign Address State PID TCP 0.0.0.0:80 0.0.0.0:0 LISTENING 4

    c. If it's not listening on the configured port, check your web server settings. For example:site bindings in IIS, server block in NGINX and virtual host in Apache.

    d. Check your OS firewall settings to make sure that incoming traffic to the port is allowed.

HTTP status code mismatch

Message: Status code of the backend's HTTP response did not match the probe setting. Expected:{HTTPStatusCode0} Received:{HTTPStatusCode1}.

(Video) How to troubleshoot the most common issues on Azure resources | Azure Portal Series

Cause: After the TCP connection has been established and a TLS handshake is done (if TLS is enabled), Application Gateway will send the probe as an HTTP GET request to the backend server. As described earlier, the default probe will be to <protocol>://127.0.0.1:<port>/, and it considers response status codes in the rage 200 through 399 as Healthy. If the server returns any other status code, it will be marked as Unhealthy with this message.

Solution: Depending on the backend server's response code, you can take the following steps. A few of the common status codes are listed here:

ErrorActions
Probe status code mismatch: Received 401Check whether the backend server requires authentication. Application Gateway probes can't pass credentials for authentication. Either allow "HTTP 401" in a probe status code match or probe to a path where the serverdoesn't require authentication.
Probe status code mismatch: Received 403Access forbidden. Check whetheraccess to the path is allowed on the backend server.
Probe status code mismatch: Received 404Page not found. Check whether the host name path is accessible on the backend server. Change the host name or path parameter to an accessible value.
Probe status code mismatch: Received 405The probe requests for Application Gateway use the HTTP GET method. Check whether your server allows this method.
Probe status code mismatch: Received 500Internal server error. Check the backend server's health and whether the services are running.
Probe status code mismatch: Received 503Service unavailable. Check the backend server's health and whether the services are running.

Or, if you think the response is legitimate and you want Application Gateway to accept other status codes as Healthy, you can create a custom probe. This approach is useful in situations where the backend website needs authentication. Because the probe requests don't carry any user credentials, they will fail, and an HTTP 401 status code will be returned by the backend server.

To create a custom probe, follow these steps.

HTTP response body mismatch

Message: Body of the backend's HTTP response did not match theprobe setting. Received response body does not contain {string}.

Cause: When you create a custom probe, you can mark a backend server as Healthy by matching a string from the response body. For example, you can configure Application Gateway to accept "unauthorized" as a string to match. If the backend server response for the probe request contains the string unauthorized, it will be marked as Healthy. Otherwise, it will be marked as Unhealthy with this message.

Solution: To resolve this issue, follow these steps:

  1. Access the backend server locally or from a client machine on the probe path, and check the response body.
  2. Verify that the response body in the Application Gateway custom probe configuration matches what's configured.
  3. If they don't match, change the probe configuration so that it has the correct string value to accept.

Learn more about Application Gateway probe matching.

Note

For all TLS related error messages, to learn more about SNI behavior and differences between the v1 and v2 SKU, check the TLS overview page.

Backend server certificate invalid CA

Message: The server certificate used by the backend is not signed by a well-known Certificate Authority (CA). Allow the backend on the Application Gateway by uploading the root certificate of the server certificate used by the backend.

Cause: End-to-end SSL with Application Gateway v2 requires the backend server's certificate to be verified in order to deem the server Healthy. For a TLS/SSL certificate to be trusted, that certificate of the backend server must be issued by a CA that's included in the trusted store of Application Gateway. If the certificate wasn't issued by a trusted CA (for example, if a self-signed certificate was used), users should upload the issuer's certificate to Application Gateway.

Solution: Follow these steps to export and upload the trusted root certificate to Application Gateway. (These steps are for Windows clients.)

  1. Sign in to the machine where your application is hosted.
  2. Select Win+R or right-click the Start button, and then select Run.
  3. Enter certmgr.msc and select Enter. You can also search for Certificate Manager on the Start menu.
  4. Locate the certificate, typically in \Certificates - Current User\\Personal\\Certificates\, and open it.
  5. Select the root certificate and then select View Certificate.
  6. In the Certificate properties, select the Details tab.
  7. On the Details tab, select the Copy to File option and save the file in the Base-64 encoded X.509 (.CER) format.
  8. Open the Application Gateway HTTP Settings page in the Azure portal.
  9. Open the HTTP settings, select Add Certificate, and locate the certificate file that you saved.
  10. Select Save to save the HTTP settings.

Alternatively, you can export the root certificate from a client machine by directly accessing the server (bypassing Application Gateway) through browser and exporting the root certificate from the browser.

For more information about how to extract and upload Trusted Root Certificates in Application Gateway, see Export trusted root certificate (for v2 SKU).

Trusted root certificate mismatch

Message: The root certificate of the server certificate used by the backend does not match the trusted root certificate added to the application gateway. Ensure that you add the correct root certificate to whitelist the backend.

Cause: End-to-end SSL with Application Gateway v2 requires the backend server's certificate to be verified in order to deem the server Healthy. For a TLS/SSL certificate to be trusted, the backend server certificate must be issued by a CA that's included in the trusted store of Application Gateway. If the certificate wasn't issued by a trusted CA (for example, a self-signed certificate was used), users should upload the issuer's certificate to Application Gateway.

The certificate that has been uploaded to Application Gateway HTTP settings must match the root certificate of the backend server certificate.

Solution: If you receive this error message, there's a mismatch between the certificate that has been uploaded to Application Gateway and the one that was uploaded to the backend server.

(Video) App Service Application Gateway Configuration

Follow steps 1-10 in the preceding section to upload the correct trusted root certificate to Application Gateway.

For more information about how to extract and upload Trusted Root Certificates in Application Gateway, see Export trusted root certificate (for v2 SKU).

Note

This error can also occur if the backend server doesn't exchange the complete chain of the cert, including the Root Intermediate (if applicable) Leaf during the TLS handshake. To verify, you can use OpenSSL commands from any client and connect to the backend server by using the configured settings in the Application Gateway probe.

For example:

OpenSSL> s_client -connect 10.0.0.4:443 -servername www.example.com -showcerts

If the output doesn't show the complete chain of the certificate being returned, export the certificate again with the complete chain, including the root certificate. Configure that certificate on your backend server.

 CONNECTED(00000188)\ depth=0 OU = Domain Control Validated, CN = \*.example.com\ verify error:num=20:unable to get local issuer certificate\ verify return:1\ depth=0 OU = Domain Control Validated, CN = \*.example.com\ verify error:num=21:unable to verify the first certificate\ verify return:1\ \-\-\-\ Certificate chain\ 0 s:/OU=Domain Control Validated/CN=*.example.com\ i:/C=US/ST=Arizona/L=Scottsdale/O=GoDaddy.com, Inc./OU=http://certs.godaddy.com/repository//CN=Go Daddy Secure Certificate Authority - G2\ \-----BEGIN CERTIFICATE-----\ xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx\ \-----END CERTIFICATE-----

Backend certificate invalid common name (CN)

Message: The Common Name (CN) of the backend certificate does not match the host header of the probe.

Cause: Application Gateway checks whether the host name specified in the backend HTTP settings matches that of the CN presented by the backend server’s TLS/SSL certificate. This verification is Standard_v2 and WAF_v2 SKU (V2) behavior. The Standard and WAF SKU (v1) Server Name Indication (SNI) is set as the FQDN in the backend pool address. For more information on SNI behavior and differences between v1 and v2 SKU, see Overview of TLS termination and end to end TLS with Application Gateway.

In the v2 SKU, if there's a default probe (no custom probe has been configured and associated), SNI will be set from the host name mentioned in the HTTP settings. Or, if “Pick host name from backend address” is mentioned in the HTTP settings, where the backend address pool contains a valid FQDN, this setting will be applied.

If there's a custom probe associated with the HTTP settings, SNI will be set from the host name mentioned in the custom probe configuration. Or, if Pick hostname from backend HTTP settings is selected in the custom probe, SNI will be set from the host name mentioned in the HTTP settings.

If Pick hostname from backend address is set in the HTTP settings, the backend address pool must contain a valid FQDN.

If you receive this error message, the CN of the backend certificate doesn't match the host name configured in the custom probe, or the HTTP settings if Pick hostname from backend HTTP settings is selected. If you're using a default probe, the host name will be set as 127.0.0.1. If that’s not a desired value, you should create a custom probe and associate it with the HTTP settings.

Solution:

To resolve the issue, follow these steps.

For Windows:

  1. Sign in to the machine where your application is hosted.
  2. Select Win+R or right-click the Start button and select Run.
  3. Enter certmgr.msc and select Enter. You can also search for Certificate Manager on the Start menu.
  4. Locate the certificate (typically in \Certificates - Current User\\Personal\\Certificates), and open the certificate.
  5. On the Details tab, check the certificate Subject.
  6. Verify the CN of the certificate from the details and enter the same in the host name field of the custom probe or in the HTTP settings (if Pick hostname from backend HTTP settings is selected). If that's not the desired host name for your website, you must get a certificate for that domain or enter the correct host name in the custom probe or HTTP setting configuration.

For Linux using OpenSSL:

  1. Run this command in OpenSSL:

    openssl x509 -in certificate.crt -text -noout
  2. From the properties displayed, find the CN of the certificate and enter the same in the host name field of the http settings. If that's not the desired host name for your website, you must get a certificate for that domain or enter the correct host name in the custom probe or HTTP setting configuration.

Backend certificate is invalid

Message: Backend certificate is invalid. Current date is not within the "Valid from" and "Valid to" date range on the certificate.

(Video) Application Gateway Multi Site Configuration - Step by Step Demo

Cause: Every certificate comes with a validity range, and the HTTPS connection won't be secure unless the server's TLS/SSL certificate is valid. The current data must be within the valid from and valid to range. If it's not, the certificate is considered invalid, and that will create asecurity issue in which Application Gateway marks the backend server as Unhealthy.

Solution: If your TLS/SSL certificate has expired, renew the certificatewith your vendor and update the server settings with the newcertificate. If it's a self-signed certificate, you must generate a valid certificate and upload the root certificate to the Application Gateway HTTP settings. To do that, follow these steps:

  1. Open your Application Gateway HTTP settings in the portal.
  2. Select the setting that has the expired certificate, select Add Certificate, and open the new certificate file.
  3. Remove the old certificate by using the Delete icon next to the certificate, and then select Save.

Certificate verification failed

Message: The validity of the backend certificate could not be verified. To find out the reason, check OpenSSL diagnostics for the message associated with error code {errorCode}

Cause: This error occurs when Application Gateway can't verify the validity of the certificate.

Solution: To resolve this issue, verify that the certificate on your server was created properly. For example, you can use OpenSSL to verify the certificate and its properties and then try reuploading the certificate to the Application Gateway HTTP settings.

Backend health status: unknown

If the backend health is shown as Unknown, the portal view will resemble the following screenshot:

Troubleshoot backend health issues in Azure Application Gateway (2)

This behavior can occur for one or more of the following reasons:

  1. The NSG on the Application Gateway subnet is blocking inbound access to ports 65503-65534 (v1 SKU) or 65200-65535 (v2 SKU) from “Internet."
  2. The UDR on the Application Gateway subnet is set to the default route (0.0.0.0/0) and the next hop is not specified as "Internet."
  3. The default route is advertised by an ExpressRoute/VPN connection to a virtual network over BGP.
  4. The custom DNS server is configured on a virtual network that can't resolve public domain names.
  5. Application Gateway is in an Unhealthy state.

Solution:

  1. Check whether your NSG is blocking access to the ports 65503-65534 (v1 SKU) or 65200-65535 (v2 SKU) from Internet:

    a.On the Application Gateway Overview tab, select the Virtual Network/Subnet link.b.On the Subnets tab of your virtual network, select the subnet where Application Gateway has been deployed.c.Check whether any NSG is configured.d.If an NSG is configured, search for that NSG resource on the Search tab or under All resources.e.In the Inbound Rules section, add an inbound rule to allow destination port range 65503-65534 for v1 SKU or 65200-65535 v2 SKU with the Source set as GatewayManager service tag.f.Select Save and verify that you can view the backend as Healthy. Alternatively, you can do that through PowerShell/CLI.

  2. Check whether your UDR has a default route (0.0.0.0/0) with the next hop not set as Internet:

    a.Follow steps 1a and 1b to determine your subnet.b.Check whether there's any UDR configured. If there is, search for the resource on the search bar or under All resources.c.Check whether there are any default routes (0.0.0.0/0) with the next hop not set as Internet. If the setting is either Virtual Appliance or Virtual Network Gateway, you must make sure that your virtual appliance, or the on-premises device, can properly route the packet back to the internet destination without modifying the packet.d.Otherwise, change the next hop to Internet, select Save, and verify the backend health.

  3. Default route advertised by the ExpressRoute/VPN connection to the virtual network over BGP:

    a.If you have an ExpressRoute/VPN connection to the virtual network over BGP, and if you are advertising a default route, you must make sure that the packet is routed back to the internet destination without modifying it. You can verify by using the Connection Troubleshoot option in the Application Gateway portal.b.Choose the destination manually as any internet-routable IP address like 1.1.1.1. Set the destination port as anything, and verify the connectivity.c.If the next hop is virtual network gateway, there might be a default route advertised over ExpressRoute or VPN.

  4. If there's a custom DNS server configured on the virtual network, verify that the servers can resolve public domains. Public domain name resolution might be required in scenarios where Application Gateway must reach out to external domains like OCSP servers or to check the certificate’s revocation status.

  5. To verify that Application Gateway is healthy and running, go to the Resource Health option in the portal, and verify that the state is Healthy. If you see an Unhealthy or Degraded state, contact support.

  6. If Internet and private traffic are going through an Azure Firewall hosted in a secured Virtual hub (using Azure Virtual WAN Hub):

    a. To ensure the application gateway can send traffic directly to the Internet, configure the following user defined route:

    Address prefix: 0.0.0.0/0
    Next hop: Internet

    (Video) Application Gateway Configuration Step by Step | Azure App Gateway Tutorial

    b. To ensure the application gateway can send traffic to the backend pool via an Azure Firewall in the Virtual WAN hub, configure the following user defined route:

    Address Prefix: Backend pool subnet
    Next hop: Azure Firewall private IP address

Next steps

Learn more about Application Gateway diagnostics and logging.

FAQs

How do I troubleshoot Azure Application Gateway? ›

Solution
  1. Check NSGs associated with the application gateway subnet. Ensure that communication to backend isn't blocked.
  2. Check UDR associated with the application gateway subnet. Ensure that the UDR isn't directing traffic away from the backend subnet.
11 Apr 2022

What is health probe in Azure Application Gateway? ›

Health probes are used to check whether one or more units in the backend pool are working correctly. The application gateway will send different requests, HTTP or HTTPS, to see if those units are working correctly, and if they are not, they will not be used for backend redirection of the client requests.

How do I monitor Azure Application Gateway? ›

Monitoring overview page in Azure portal

The Overview page in the Azure portal for each Application Gateway includes the following metrics: Sum Total Requests. Sum Failed Requests. Sum Response Status by HttpStatus.

What are the types of listeners in Application Gateway? ›

There are two types of listeners: Basic. This type of listener listens to a single domain site, where it has a single DNS mapping to the IP address of the application gateway. This listener configuration is required when you host a single site behind an application gateway.

How do you know if your back and pool members are healthy? ›

To check the health of your backend pool, you can use the Backend Health page on the Azure portal. Or, you can use Azure PowerShell, CLI, or REST API.
...
The status retrieved by any of these methods can be any one of the following states:
  • Healthy.
  • Unhealthy.
  • Unknown.
20 Jul 2022

What is Azure Application Gateway 502 error? ›

After you configure an application gateway, one of the errors that you may see is Server Error: 502 - Web server received an invalid response while acting as a gateway or proxy server. This error may happen for the following main reasons: NSG, UDR, or Custom DNS is blocking access to backend pool members.

What is difference between Azure load balancer and Application Gateway? ›

Traditional load balancers operate at the transport layer (OSI layer 4 - TCP and UDP) and route traffic based on source IP address and port, to a destination IP address and port. Application Gateway can make routing decisions based on additional attributes of an HTTP request, for example URI path or host headers.

What is the difference between Azure Application Gateway load balancer front door and firewall? ›

What is the difference between Azure Front Door and Azure Application Gateway? While both Front Door and Application Gateway are layer 7 (HTTP/HTTPS) load balancers, the primary difference is that Front Door is a non-regional service whereas Application Gateway is a regional service.

What types of logs does application gateway provide? ›

For Application Gateway, three logs are available: Access log. Performance log. Firewall log.

What is a backend pool? ›

The backend pool is a critical component of the load balancer. The backend pool defines the group of resources that will serve traffic for a given load-balancing rule. There are two ways of configuring a backend pool: Network Interface Card (NIC)

How do I test my application gateway? ›

Test the application gateway

Find the public IP address for the application gateway on its Overview page. Or, you can select All resources, enter myAGPublicIPAddress in the search box, and then select it in the search results. Azure displays the public IP address on the Overview page.

What is unhealthy host count in Azure? ›

Unhealthy host count

The number of backends that are determined unhealthy by the health probe. You can filter on a per backend pool basis to show the number of unhealthy hosts in a specific backend pool.

How do I restart Azure Application Gateway? ›

As of now, there is no option from the Azure portal to reboot an application gateway resource(Stop and Start). Now we will be using the Azure cloud shell to reboot the application gateway.

What are the health monitor states in Big-IP? ›

The BIG-IP system provides the following pre-configured monitor types: tcp, http, https, and https_443.

How do I fix 502 Web server received an invalid response while acting as a gateway or proxy server? ›

  1. DNS Issue. A 502 gateway error could also be because of a DNS issue, such as the domain is not resolving to the correct IP, or the DNS server is not responding. ...
  2. Check With Your Host. ...
  3. Temporarily Disable CDN or Firewall. ...
  4. Check Your Plugins and Themes. ...
  5. Check Logs. ...
  6. Restart PHP. ...
  7. PHP Timeout Issue.

What does bad gateway mean on a website? ›

A 502 bad gateway message indicates that one server got an invalid response from another. In essence, you've connected with some kind of interim device (like an edge server) that should fetch all of the bits you need to load the page. Something about that process went wrong, and the message indicates the problem.

How do I find my Application Gateway SKU? ›

Example 1: Get an application gateway SKU

The first command gets the Application Gateway named ApplicationGateway01 and stores the result in the variable named $AppGW. The second command gets the SKU of an application gateway named ApplicationGateway01 and stores the result in the variable named $SKU.

Is Azure Application Gateway IaaS or PaaS? ›

Azure provides software as a service (SaaS), platform as a service (PaaS) and infrastructure as a service (IaaS). The platform supports many programming languages and frameworks and can be used alone or in a multi-vendor cloud environment.

What is l7 Application Gateway? ›

Azure Application Gateway offers a Layer 7 load-balancing feature for HTTP and HTTPs traffic, and you can route traffic based on the incoming URL. HTTP Traffic requests are routed in a round-robin method to the backend servers.

What is the difference between traffic manager and Application Gateway? ›

Traffic Manager & Application Gateway - Traffic Manager provides DNS-based load balancing, while the Application Gateway gives you many of the same capabilities as Azure Front Door but at the regional level such as: Web Application Firewall (WAF) Transport Layer Security (TLS) termination. Path-based routing.

How do I check my health probe Azure? ›

Health probes originate from an Azure infrastructure address and are visible within the guest OS of the VM. To get the health probe status for your standard load balancer resources: Select the Health Probe Status metric with Avg aggregation type. Apply a filter on the required frontend IP address or port (or both).

What is load balancing rule in Azure? ›

Load-balancing rules - A load balancer rule is used to define how incoming traffic is distributed to the all the instances within the backend pool. A load-balancing rule maps a given frontend IP configuration and port to multiple backend IP addresses and ports.

How do I get a health check? ›

On the Create a health check page, supply the following information:
  1. Name: Provide a name for the health check.
  2. Description: Optionally, provide a description.
  3. Scope: Select a scope, either Global or Regional, depending on the type of load balancer. ...
  4. Protocol: Choose a health check protocol.
  5. Port: Provide a port number.

Is Azure Application Gateway a reverse proxy? ›

Azure Application Gateway is a managed web traffic load balancer and HTTP(S) full reverse proxy that can do Secure Socket Layer (SSL) encryption and decryption.

What OSI layer does a WAF work on? ›

A WAF is a protocol layer 7 defense (in the OSI model), and is not designed to defend against all types of attacks. This method of attack mitigation is usually part of a suite of tools which together create a holistic defense against a range of attack vectors.

What is one advantage that Azure load balancer has over an Azure Application Gateway? ›

Azure Load Balancer provides basic load balancing based on 2 or 5 tuple matches. Load Balancer only supports endpoints hosted in Azure. Application Gateway can support any routable IP address.

How do I check WAF logs? ›

Inspecting Web Application Firewall logs
  1. From: https://docs.microsoft.com/en-us/azure/frontdoor/waf-overview. ...
  2. OWASP ZAP tool. ...
  3. WAF policy set to Detection; start with detection to learn what the rules might block in your app. ...
  4. Blocked requests (if the policy were set at Prevention at the global level) ...
  5. Typical SQL Injection.
25 Jun 2019

How do I check my Azure App Service log? ›

Log detailed errors

To save the error page or failed request tracing for Windows apps in the Azure portal, navigate to your app and select App Service logs. Under Detailed Error Logging or Failed Request Tracing, select On, then select Save. Both types of logs are stored in the App Service file system.

What is back end pool in Azure? ›

The backend pool is a critical component of the load balancer. The backend pool defines the group of resources that will serve traffic for a given load-balancing rule. There are two ways of configuring a backend pool: Network Interface Card (NIC)

How do you build a backend pool in Azure? ›

Select myVNet in Virtual network. Select IP Address for Backend Pool Configuration. Select Save. Select Next: Inbound rules at the bottom of the page.
...
During the creation of the load balancer, you'll configure:
  1. Frontend IP address.
  2. Backend pool.
  3. Inbound load-balancing rules.
  4. Health probe.
14 Sept 2022

What is backend service in load balancer? ›

A backend service defines how Cloud Load Balancing distributes traffic. The backend service configuration contains a set of values, such as the protocol used to connect to backends, various distribution and session settings, health checks, and timeouts.

What is connection draining in application gateway? ›

Connection draining helps you achieve graceful removal of backend pool members during planned service updates. This setting is enabled via the backend http setting and can be applied to all members of a backend pool during rule creation.

How do I enable WAF on application gateway? ›

Detection: Monitors and logs all threat alerts into a log file if we run WAF in “Detection” mode.
...
Step 2:
  1. Select the Subscription.
  2. Select the Resource group.
  3. Enter the Application gateway name.
  4. Select Region.
  5. Select Tier to either “WAF” or “WAF V2”
  6. In case you select WAF, Enter the Instance count.
28 Dec 2020

What is the difference between API gateway provided by Azure API Management and Azure application gateway? ›

API Management (APIM) is superior to API gateway where it does all the activities of API Gateway and also do additional activities like Service dictionary, Service directory lookup, monitoring services and handle security functionalities to service invocation through SSL certificates.

What is probe in load balancer? ›

Azure Load Balancer rules require a health probe to detect the endpoint status. The configuration of the health probe and probe responses determines which backend pool instances will receive new connections. Use health probes to detect the failure of an application.

How do I restart Azure Application Gateway? ›

As of now, there is no option from the Azure portal to reboot an application gateway resource(Stop and Start). Now we will be using the Azure cloud shell to reboot the application gateway.

How do I troubleshoot Azure firewall? ›

In the Azure portal, open your firewall resource group and select the firewall. Under Monitoring, select Diagnostic settings.
...
Enable diagnostic logging through the Azure portal
  1. AzureFirewallApplicationRule.
  2. AzureFirewallNetworkRule.
  3. AzureFirewallDnsProxy.
7 Dec 2021

How do you get audit logs for Azure Application Gateway? ›

Enable logging through the Azure portal
  1. In the Azure portal, find your resource and select Diagnostic settings. ...
  2. To start collecting data, select Turn on diagnostics.
  3. The Diagnostics settings page provides the settings for the resource logs. ...
  4. Type a name for the settings, confirm the settings, and select Save.
25 Aug 2022

What logs does Application Gateway provide? ›

For Application Gateway, three logs are available: Access log. Performance log. Firewall log.

How do I start and stop Azure Application Gateway? ›

Write-Host "Starting the application gateway." Write-Host "Stopping the application gateway." To execute the script, you need to provide the Azure subscription ID, the resource group name, the app application gateway name, and either $true (to start) or $false (to stop) to change the application gateway state.

What means Microsoft Azure Application Gateway v2? ›

Azure Application Gateway is a web traffic load balancer that enables you to manage traffic to your web applications. Traditional load balancers operate at the transport layer (OSI layer 4 - TCP and UDP) and route traffic based on source IP address and port, to a destination IP address and port.

How do I launch Azure application? ›

Build your first Web App with Microsoft Azure - YouTube

What is an application gateway Azure? ›

Azure Application Gateway is a web traffic load balancer that enables you to manage traffic to your web applications. Traditional load balancers operate at the transport layer (OSI layer 4 - TCP and UDP) and route traffic based on source IP address and port, to a destination IP address and port.

How do I create a gateway WAF policy? ›

Create a policy

Type a unique name for your WAF policy. Select the application gateway, and then select Add. Select the application gateway, select the listeners, then select Add. Select the application gateway, select the listener, select the routing rule, and then select Add.

How do I add a IP address to my Azure firewall? ›

Open the Azure Portal: https://portal.azure.com.
  1. Click on Resource Groups and then the resource group of the SQL server.
  2. In the Resource Group blade click on the SQL server.
  3. Within the “Security” Category click on “Firewall”.
  4. Add your Client IP within this blade.
  5. Click on save to save the settings.
27 Jan 2017

What are the modes available in WAF policy? ›

Front Door WAF policies support two modes of operation, detection and prevention. By default, prevention is configured. Detection - monitors and logs all requests which match a WAF rule. In this mode, the WAF doesn't take action against incoming requests.

How do I set up a log analytics workspace in Azure? ›

After you've created a workspace, configure a Log Analytics workspace in Azure Monitor by using PowerShell. Run the az group create command to create a resource group or use an existing resource group. To create a workspace, use the az monitor log-analytics workspace create command.

Videos

1. Understanding and Configuring Application Gateway
(Azure Training Series)
2. Deliver secure and scalable web applications with Azure Application Gateway
(Microsoft Azure)
3. Azure Application Gateway [FULL COURSE IN 3.5 HOURS]
(Hussein Awad)
4. Azure application gateway path-based routing
(Bee a Learner 🐝🌨️)
5. Azure Application Gateway Overview Explained in 15 minutes
(Paddy Maddy)
6. Azure Application Gateway : EP-01
(Bee a Learner 🐝🌨️)

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