Azure Application gateway

Posted: June 18, 2018 in Azure

Azure Application Gateway is a web traffic load balancer that enables  manage traffic to web applications using.Application Gateway is a layer 7 load balancer, which means it works with web traffic only (HTTP/HTTPS/WebSocket)

In Azure portal click new-Application gateway



For application gateway dedicated subnet is created (



Create availability set



and create public address


Creating Backend Pool

Backend pools can be composed of NICs, virtual machine scale sets, public IPs, internal IPs, fully qualified domain names (FQDN), and multi-tenant back-ends like Azure Web Apps. Application Gateway backend pool members are not tied to an availability set.

In resource group click on Application gateway-Backend Pools.Default pool is created-click on it



On target drop-down list select Virtual machine



Select Virtual machines (in this case there are 2 VM’s:app1 and app2


Health probes

Azure Application Gateway by default monitors the health of all resources in its back-end pool and automatically removes any resource considered unhealthy from the pool. Application Gateway continues to monitor the unhealthy instances and adds them back to the healthy back-end pool once they become available and respond to health probes.

Click on Health probes (default one is created alongside with Application gateway)



For host type, for path type /index.txt

On app1 and app2 servers,IIS is installed and under c:\intetpub\wwwroot folder index.txt file is created.It will be used as “probe” to check backed server availability (HTTP response 200)

Content of index.txt

This is server 1-on app1 machine

This is server 2-on app2 machine


Interval:Configures the probe interval checks in seconds.

Timeout:Defines the probe time-out for an HTTP response check.

UnhealthyThreshold:The number of failed HTTP responses needed to flag the back-end instance as unhealthy.


HTTP settings

Click on default HTTP settings



Select health probe and port



When a user request is received, Application Gateway applies the configured rules to the request and routes it to a back-end pool instance. It waits for a configurable interval of time for a response from the back-end instance. By default, this interval is 30 seconds. If Application Gateway does not receive a response from back-end application in this interval, user request would see a 502 error.

In Application Gateway settings,in Overview properties we can see public IP







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