I am using Azure App Service (Regional Vnet Integrated) and Paas Services Like Azure Key Vault, Azure Storage with System Managed Identity and Service endpoints enabled to access the Azure Key vault.
I am using Spring Boot Application.
And integrated the Key vault as per following doc.
https://learn.microsoft.com/en-us/java/api/overview/azure/spring-boot-starter-keyvault-secrets-readme?view=azure-java-stable
Also in App service we have set the config properties as follows:
WEBSITE_VNET_ROUTE_ALL - 1
WEBSITE_DNS_SERVER - 168.63.129.16
But i am getting below exception on application startup-
Caused by: java.net.UnknownHostException: failed to resolve '$$$$.vault.azure.net' after 2 queries
at io.netty.resolver.dns.DnsResolveContext.finishResolve(DnsResolveContext.java:1013)
... 22 common frames omitted
Caused by: io.netty.resolver.dns.DnsNameResolverTimeoutException: [/8.8.4.4:53] query via UDP timed out after 5000 milliseconds (no stack trace available)

Also similar connection issues to other Paas Services.
There is no document to follow to configure connections in such a case.
Any one faced such issue?

Hello @SonalBK843 ,

Thanks for reaching out and sorry for delayed response.

This issue seems to be more on "io.netty.resolver.dns.DnsNameResolverTimeoutException" project related than Azure Key vault.

I would request you to try out solution suggested in below GitHub issues as those were related with "io.netty" exception, meanwhile I will try to get more insight. Thanks.

https://github.com/redisson/redisson/issues/1944#issuecomment-468312630

   reactor.netty.http.client.HttpClient nettyHttpClient =  
           reactor.netty.http.client.HttpClient.create()  
               .resolver(DefaultAddressResolverGroup.INSTANCE);  
       HttpClient httpClient = new NettyAsyncHttpClientBuilder(nettyHttpClient).build();  
       CertificateClient certificateClient =  
           new CertificateClientBuilder()  
               .httpClient(httpClient)  
               .vaultUrl(keyVaultUri)  
               .credential(new ManagedIdentityCredentialBuilder().build())  
               .buildClient();  
A similar fix was done with WebClient --> https://github.com/reactor/reactor-netty/issues/1431