How do you update TableServiceClient in ASP.NET Core, to point to a secondary region, when using Azure geo redundant (RA-GRS) table storage?

Question

I am using the latest Azure.Data.Tables nuget package, version 12.3.0 to connect to Azure table storage in an ASP.NET Core C# Application.

My application needs to failover to a secondary region for reads if the primary region fails.

Currently the setup the of TableServiceClient is done in the Startup.cs as follows:

public void ConfigureServices(IServiceCollection services)
{     
   services.AddSingleton(new TableServiceClient(new Uri("PrimaryRegionConnectionURL"), new DefaultAzureCredential()));
}

How do would I update the current instance of TableServiceClient with an instance pointed to the secondary region? Is there a better approach to achieve this failover?

Just to Clarify: I am aware that the client doesn't support failing over and the team have created a ticket to look at this feature in future. I realize I need to have a new instance of TableServiceClient.

I am just not sure how I would replace the one created at startup with a new instance pointed to the secondary instance at the time of failure.

Here is that code that consumes the TableServiceClient

    public class TableRepository : ITableStorageRepository
{
    readonly TableServiceClient _serviceClient;

    public TableRepository(TableServiceClient serviceClient)
    {
        _serviceClient = serviceClient;
    }

    public async Task<ICollection<T>> GetPartitionEntities<T>(string partitionKey, string tableName)
        where T : class, ITableEntity, new()
    {
        var listOfEntities = new List<T>();

        var tableClient = _serviceClient.GetTableClient(tableName);

        var queryResults = tableClient.QueryAsync<T>(filter => filter.PartitionKey == partitionKey);

        await foreach (var row in queryResults) 
        {
            listOfEntities.Add(row);
        }

        return listOfEntities;
    }
}

@GauravMantri I am using a nuget package `Azure.Data.Tables` that is part of the `azure-sdk-for-net` found here: https://github.com/Azure/azure-sdk-for-net — SetiSeeker, Dec 15 '21 at 14:49

Gaurav Mantri · Accepted Answer · 2021-12-15T15:34:20.620

Not sure if this is the best way to accomplish it, but this is how I would have done it considering I have to handle the logic of switching between primary and secondary endpoint myself.

First, I would have created two instances of TableServiceClient - one for the primary and other for secondary.

public void ConfigureServices(IServiceCollection services)
{  
    Dictionary<string, TableServiceClient> tableServiceClients = new Dictionary()
    {
      "Primary",  new TableServiceClient(new Uri("PrimaryRegionConnectionURL"), new DefaultAzureCredential()),
      "Secondary",  new TableServiceClient(new Uri("SecondaryRegionConnectionURL"), new DefaultAzureCredential())
    }
    services.AddSingleton(tableServiceClients);
}

Next, I would have extracted the logic for fetching the entities in a separate function and passed the client to that function (let's call that GetPartitionEntitiesImpl).

Then in GetPartitionEntities method I would have tried to get the entities from the primary endpoint and catch the exception. If the exception indicates primary endpoint failure, I would have called GetPartitionEntitiesImpl function again and try to fetch the entities from the secondary endpoint.

public class TableRepository : ITableStorageRepository
{
    readonly TableServiceClient _primaryServiceClient, _secondaryServiceClient;

    public TableRepository(Dictionary<string, TableServiceClient> tableServiceClients)
    {
        _primaryServiceClient = tableServiceClients["Primary"];
        _secondaryServiceClient = tableServiceClients["Secondary"];
    }

    public async Task<ICollection<T>> GetPartitionEntities<T>(string partitionKey, string tableName)
        where T : class, ITableEntity, new()
    {
        try
        {
            return await GetPartitionEntitiesImpl(_primaryServiceClient, partitionKey, tableName);
        }
        catch (Exception exception)
        {
          //Check if there is a need for failover
          if (shouldTrySecondaryEndpoint)
          {
              return await GetPartitionEntitiesImpl(_secondaryServiceClient, partitionKey, tableName);
          }
        }
    }

    private async Task<ICollection<T>> GetPartitionEntitiesImpl<T>(TableServiceClient serviceClient, string partitionKey, string tableName)
        where T : class, ITableEntity, new()
    {
        var listOfEntities = new List<T>();

        var tableClient = serviceClient.GetTableClient(tableName);

        var queryResults = tableClient.QueryAsync<T>(filter => filter.PartitionKey == partitionKey);

        await foreach (var row in queryResults) 
        {
            listOfEntities.Add(row);
        }

        return listOfEntities;
    }

}

Also, please take a look at the code of older Azure Storage SDK (version 9.x) regarding the logic for switching between primary and secondary endpoints. That SDK handles this scenario rather well.

thank you for your solution, I think this gives me a good start many thanks. — SetiSeeker, Dec 17 '21 at 06:08

score 1 · Answer 2 · answered Dec 15 '21 at 14:42

1

Automatic failover using the same client is not currently supported; to use the secondary region, a separate TableServiceClient would be needed. More context is available here: https://github.com/Azure/azure-sdk-for-net/issues/25456

Work for adding support is being tracked here: https://github.com/Azure/azure-sdk-for-net/issues/25710

answered Dec 15 '21 at 14:42

Jesse Squire

6,107
1
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Hi Jesse, I am aware that the client doesn't support this, and realize I need to have a new instance of `TableServiceClient`. I am just not sure how I would replace the one created at startup with a new instance pointed to the secondary instance at the time of failure. Thank you for your reply. – SetiSeeker Dec 15 '21 at 14:46
Hi Jesse I have updated the question to try and make it clearer, and thank you to the team for tracking my failover question. – SetiSeeker Dec 15 '21 at 14:55
Can you please edit your question and include code where you are using TableServiceClient? – Gaurav Mantri Dec 15 '21 at 14:56
@GauravMantri that code is in the original post as is the nuget package and verion – SetiSeeker Dec 15 '21 at 14:57
You included the code where you're configuring the dependency. I was more interested in seeing the code where you're injecting this dependency. It is quite clear that you will need 2 different TableServiceClient instances at least as of now - one pointing to the primary endpoint and other to secondary endpoint. – Gaurav Mantri Dec 15 '21 at 15:00
@GauravMantri Thank you for clarifying, I will add the code – SetiSeeker Dec 15 '21 at 15:04
Added an answer. Not sure if this is the best approach but it should give you some idea about how to proceed. Please do share the solution you come up. I would be very much interested in knowing about that. – Gaurav Mantri Dec 15 '21 at 15:27

How do you update TableServiceClient in ASP.NET Core, to point to a secondary region, when using Azure geo redundant (RA-GRS) table storage?

2 Answers2