Service Bus Concurrency Setup in Function app isolated model

Question

I'm migrating my in process functions to isolated. While migrating I'm having this difficulty: It seems like ServiceBus's maxConcurrentCalls can only be set using host.json file.

{
    "version": "2.0",
    "extensions": {
        "serviceBus": {
            "clientRetryOptions":{
                "mode": "exponential",
                "tryTimeout": "00:01:00",
                "delay": "00:00:00.80",
                "maxDelay": "00:01:00",
                "maxRetries": 3
            },
            "prefetchCount": 0,
            "transportType": "amqpWebSockets",
            "webProxy": "https://proxyserver:8080",
            "autoCompleteMessages": true,
            "maxAutoLockRenewalDuration": "00:05:00",
            "maxConcurrentCalls": 16,
            "maxConcurrentSessions": 8,
            "maxMessageBatchSize": 1000,
            "minMessageBatchSize": 1,
            "maxBatchWaitTime": "00:00:30",
            "sessionIdleTimeout": "00:01:00",
            "enableCrossEntityTransactions": false
        }
    }
}

In the old process, in-process model, we were able handle the maxConcurrancy using appsettings.json

var serviceBusMaxConcurrentCalls = 
    Configuration.GetValue<int>("AppConfig:ServiceBus:Concurrency:MaxConcurrentCalls");

var serviceBusMaxConcurrentSessions = 
    Configuration.GetValue<int>("AppConfig:ServiceBus:Concurrency:MaxConcurrentSessions");

var serviceBusMaxConcurrentCallsPerSession = 
    Configuration.GetValue<int>("AppConfig:ServiceBus:Concurrency:MaxConcurrentCallsPerSession");

services.Configure<ServiceBusOptions>(options =>
    {
        options.MaxConcurrentCalls = serviceBusMaxConcurrentCalls;
        options.MaxConcurrentSessions = serviceBusMaxConcurrentSessions;
        options.MaxConcurrentCallsPerSession = serviceBusMaxConcurrentCallsPerSession;
        options.AutoCompleteMessages = false;
    }
);

Is there a way to still manage the concurrency using the appsettings? Or do we have to maintain an environment-specific host.json file?

I think this answer will help u stackoverflow.com/questions/77834609/… — D A
– D A, Commented Jul 24 at 7:25

Disco Globeulon · Accepted Answer · 2025-07-29 16:05:37Z

If you want to keep you service bus configuration in appsettings, you'll have to add the configuration provider in your Program.cs file:

builder.Configuration
    .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
    .AddEnvironmentVariables(); // Also adds env variables to the config if you need

Then if you like, create an options class around your appsettings.json. Using your example:

public class AppConfig
{
    public ServiceBus ServiceBus {  get; set; }
    // whatever else you need in your appsettings.json
}

public class ServiceBus  
{
    public Concurrency Concurrency { get; set; }
}

public class Concurrency
{
    public int MaxConcurrentCalls { get; set; }
    public int MaxConcurrentSessions { get; set; }
    public int MaxConcurrentCallsPerSession { get; set; }
}

You can add the following in your Program.cs to register the Options class:

builder.Services.Configure<AppConfig>(
    builder.Configuration.GetSection("AppConfig"));

And the following to configure service bus trigger concurrency like you want:

builder.Services.Configure<ServiceBusOptions>(options =>
{
    var settings = builder.Configuration
                          .GetSection("AppConfig")
                          .Get<AppConfig>();

    options.MaxConcurrentCalls = settings.ServiceBus.Concurrency.MaxConcurrentCalls;
    options.MaxConcurrentSessions = settings.ServiceBus.Concurrency.MaxConcurrentSessions;
    options.MaxConcurrentCallsPerSession = settings.ServiceBus.Concurrency.MaxConcurrentCallsPerSession;
});

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