Azure App service are having two kinds of hostings
- Single Tenant (App Service Environment) which is dedicated to the customer
- Multi tenant ( shareable across other customer subscription inside a data center scale unit)
If your application is hosted as multi tenant application meaning app service URL {WEbAppName}.Azurewebsites.net then its internet facing application and if it needs to connect to any VNET (Virtual Network) hosted service then it needs to integrate to any or same VNET.
How to do App service VNET Integration:
https://learn.microsoft.com/en-us/azure/app-service/overview-vnet-integration#regional-virtual-network-integration
Once the App service integrated with VNET then ideally it has connectivity with all the services present inside the same VNET or with peered VNET.
How to confirm connectivity from App Service to VNET hosted resource.
Go to App Services application => Advanced tools or console => perform below commands sequence wise as the HTTP communication happens through this sequence:
- nslookup {Destination_FQDN} {Optional-DNSServer}/nameresolver {Destination_FQDN} {Optional-DNSServer}
- tcpping {Destination FQDN}
- curl -v {DestinationFQDN}
Common Scenarios:
If you're receiving connection refused it means its NSG is not allowing the communication.
If you're getting request time out it means it could be due to firewall or no proper routes to reach to destination.
If its connection abort it means its intermediate device is not passing connection through.
Troubleshoot connectivity issues using Azure Network Watcher: https://learn.microsoft.com/en-us/azure/network-watcher/network-watcher-connectivity-portal