System.ArgumentOutOfRangeException List of configured name servers must not be empty. Parameter name: servers

[sathishkumarkaliavaradhan]

I have upgraded the Microsoft.Extensions.Configuration.AzureAppConfiguration nuget package from 6.0.0 to 8.0.0 now I am getting the below crash from our clients.

`async Task<IDnsQueryResponse> LookupClient.QueryInternalAsync(DnsQuestion question, DnsQuerySettings queryOptions, IReadOnlyCollection<NameServer> servers, CancellationToken cancellationToken)
In App
Assembly:DnsClient Version:1.7.0.0 PublicKeyToken:4574bb5573c51424`
Called from: async Task<IEnumerable<SrvRecord>> SrvLookupClient.InternalQueryAsync(string srvDns, CancellationToken cancellationToken)
async Task<IEnumerable<SrvRecord>> SrvLookupClient.QueryAsync(string host, CancellationToken cancellationToken)
async Task ConfigurationClientManager.RefreshFallbackClients(CancellationToken cancellationToken)
async Task ConfigurationClientManager.DiscoverFallbackClients()

System.ArgumentOutOfRangeException: List of configured name servers must not be empty.
Parameter name: servers
Exception fatal 08:56:28.941 PM
A Task's exception(s) were not observed either by Waiting on the Task or accessing its Exception property. As a result, the unobserved exception was rethrown by the finalizer thread.

Below is the CDN configuration, we are connecting the feature flag via CDN link

private const string DefaultConnectionString = "Endpoint=https://xxxxxx-edge.azureedge.net;Id=0;Secret=MA==";

configurationBuilder.AddAzureAppConfiguration(options =>
{
    // To connect with feature flag CDN edge.
    options.Connect(this.connectionString);
    options.UseFeatureFlags(config => config.SetRefreshInterval(this.Configuration.ConfigurationRefreshInterval));
    this.configurationRefresher = options.GetRefresher();
}, true);

var serviceCollection = new ServiceCollection();
serviceCollection.Configure<FeatureManagementOptions>(options =>
{
    options.IgnoreMissingFeatures = false;
    // The 'IgnoreMissingFeatureFilters' flag cannot be used in combination with a feature of requirement type 'All'.
    options.IgnoreMissingFeatureFilters = false;                
});

serviceCollection.AddSingleton<IConfiguration>(configuration)
    .AddFeatureManagement()
    .AddFeatureFilter<ContextualTargetingFilter>()
    .AddFeatureFilter<DeviceFilter>();

var seviceProvider = serviceCollection.BuildServiceProvider();
this.featuremanager = seviceProvider.GetService<IFeatureManager>();

During the initialization of SDK throws the above exception.

Could you please let me know how do I fix this issue? I also see the latest version 8.2.0, is it fixed in the latest version?

Thanks,
Sathishkumar

[sathishkumarkaliavaradhan]

@zhiyuanliang-ms ^^^

[RichardChen820]

This is a new feature introduced in v7.1.0 — auto replica discovery. From the error, it appears that your server is likely not configured with a name server. The .NET provider should handle this case, if no name servers can be found, replica discovery should be skipped.

As a workaround at this moment, you can set options.ReplicaDiscoveryEnabled = false to disable this feature.
For more details, see:
https://learn.microsoft.com/en-us/azure/azure-app-configuration/howto-geo-replication?tabs=dotnet#automatic-replica-discovery

[zhiyuanliang-ms]

private const string DefaultConnectionString = "Endpoint=https://xxxxxx-edge.azureedge.net;Id=0;Secret=MA==";

configurationBuilder.AddAzureAppConfiguration(options =>
{
    // To connect with feature flag CDN edge.
    options.Connect(this.connectionString);
    options.UseFeatureFlags(config => config.SetRefreshInterval(this.Configuration.ConfigurationRefreshInterval));
    this.configurationRefresher = options.GetRefresher();
}, true);

Your code snippet is interesting, I believe that the format: "Endpoint=xxx;Id=xxx;Secret=xxx" is only accepted by App Config SDK. Here is the code implementation. We are using HMAC authentication when using connection string. I am curious what is the Id and Secret part in your connection string with endpoint pointed to your CDN.

Did you just copy the id and secret from your original connection string of your App Config store?

How do you implement/configure your "Azure Edge" cdn?

[sathishkumarkaliavaradhan]

Thanks @RichardChen820 for your response. I will try to disable this feature.

@zhiyuanliang-ms We have followed the Microsoft recommendation from below document and worked fine before upgrading the SDK version to 8.0.0

Edge delivery setup for Azure AppConfiguration (1).docx

Did you just copy the id and secret from your original connection string of your App Config store?
No, I just used the string ";Id=0;Secret=MA==" which mentioned on the above document.

Should i use only CDN endpoint Url only without Id and Secret parameter in connection string?
"Endpoint=https://xxxxxx-edge.azureedge.net"

How do you implement/configure your "Azure Edge" cdn?
I have followed the attached MS recommendation to configure the CDN.

Please let me know if there is any change in the original recommendation.

Thanks,
Sathishkumar

[sathishkumarkaliavaradhan]

@zhiyuanliang-ms could you please let me know the recommended way to connect/configure your "Azure Edge" cdn?

[zhiyuanliang-ms]

Hi, @sathishkumarkaliavaradhan

Azure Front Door recently made authentication with managed identity public preview. We are working on our CDN solution. We have PR #601. I believe the solution will be out in one month.

For now, you can reference the implementation in #601 where we used an empty token credential. CDN should work as a proxy between client and App Config service. When client talks with CDN, I suppose there is no authentication, but it depends on how you implement your CDN.

[avanigupta]

@sathishkumarkaliavaradhan did the workaround to disable replica discovery fix your issue?
If yes, I think you can continue using the CDN setup with dummy connection string like you have today. Our original recommendation from the doc you linked has not changed.

Additionally, as @zhiyuanliang-ms pointed out, we are working on officially supporting a more seamless integration with CDN where you wouldn't need to worry about dummy credentials or a gateway like Azure Functions for authentication. When that is released, we will provide new documentation on how to set it up.

[sathishkumarkaliavaradhan]

@avanigupta Thanks for your reply.

I couldn't reproduce this issue locally on my machine but we are getting the telemetry from customer machine. For now I disabling disable replica discovery and monitoring it. I will update you if it's still happening in our customer environment.

Let me know once the documentation gets updated for CDN edge connectivity, I will upgrade the NuGet package to connect the CDN using the different methods.