dotnet/yarp · critical · ArgumentException

At least one IProxyConfigProvider is required.

Error message

At least one IProxyConfigProvider is required.

What it means

The `ProxyConfigManager` constructor requires at least one `IProxyConfigProvider` to be registered in the DI container. YARP's configuration model is entirely driven by config providers (e.g., `LoadFromConfig`, `InMemoryConfigProvider`, or custom implementations). If none are registered, the proxy has no routes or clusters and cannot function, so construction fails immediately with an `ArgumentException`.

Source

Thrown at src/ReverseProxy/Management/ProxyConfigManager.cs:103

        ArgumentNullException.ThrowIfNull(configChangeListeners);
        ArgumentNullException.ThrowIfNull(destinationResolver);

        _logger = logger;
        _providers = providers.ToArray();
        _clusterChangeListeners = clusterChangeListeners.ToArray();
        _filters = filters.ToArray();
        _configValidator = configValidator;
        _proxyEndpointFactory = proxyEndpointFactory;
        _transformBuilder = transformBuilder;
        _httpClientFactory = httpClientFactory;
        _activeHealthCheckMonitor = activeHealthCheckMonitor;
        _clusterDestinationsUpdater = clusterDestinationsUpdater;
        _destinationResolver = destinationResolver;
        _configChangeListeners = configChangeListeners.ToArray();

        if (_providers.Length == 0)
        {
            throw new ArgumentException($"At least one {nameof(IProxyConfigProvider)} is required.", nameof(providers));
        }

        _configs = new ConfigState[_providers.Length];

        _conventions = new List<Action<EndpointBuilder>>();
        DefaultBuilder = new ReverseProxyConventionBuilder(_conventions);

        _endpointsChangeToken = new CancellationChangeToken(_endpointsChangeSource.Token);
    }

    public ReverseProxyConventionBuilder DefaultBuilder { get; }

    // EndpointDataSource

    /// <inheritdoc/>
    public override IReadOnlyList<Endpoint> Endpoints
    {
        get

View on GitHub (pinned to bd11867bee)

Solutions

1. Call `.LoadFromConfig(builder.Configuration.GetSection("ReverseProxy"))` after `AddReverseProxy()` to register the configuration-based provider.
2. Alternatively, call `.LoadFromMemory(routes, clusters)` to provide routes and clusters programmatically.
3. If using a custom `IProxyConfigProvider`, register it with `services.AddSingleton<IProxyConfigProvider, MyCustomProvider>()` before the proxy starts.
4. Verify in `Program.cs` that the `AddReverseProxy()` chain includes at least one config-loading method before `app.Run()`.

Example fix

// before — no config provider registered, throws at startup
builder.Services.AddReverseProxy();
// after — load from appsettings.json
builder.Services
    .AddReverseProxy()
    .LoadFromConfig(builder.Configuration.GetSection("ReverseProxy"));
// or load from memory
builder.Services
    .AddReverseProxy()
    .LoadFromMemory(myRoutes, myClusters);

// After AddReverseProxy, verify a provider is registered
var providers = builder.Services.Where(s => s.ServiceType == typeof(IProxyConfigProvider)).ToList();
if (providers.Count == 0)
    throw new InvalidOperationException("AddReverseProxy requires at least one config provider via LoadFromConfig or LoadFromMemory");

// No type guard — this is a DI registration completeness check.

// Not applicable — this is a startup-time validation error.
// Fix by registering a config provider.

When it happens

Trigger: `services.AddReverseProxy()` is called but no `.LoadFromConfig(...)` or `.LoadFromMemory(...)` follows it before the application starts. The `ProxyConfigManager` receives an empty `IProxyConfigProvider[]` array from DI and throws at line 103. This surfaces as a startup crash during service resolution.

Common situations: A developer adds `AddReverseProxy()` during initial scaffolding but hasn't yet wired up a config source. A developer writes a custom config provider but forgets to register it in DI. Someone removes the `.LoadFromConfig(configuration)` call while refactoring Program.cs.

Related errors

• The route config format has changed, routes are now objects
• Unable to load or apply the proxy configuration.
• ConfigureHttpClient will override the custom IForwarderHttpC
• Configuration Filter Error: Substitution for '{lookup}' in c
• Missing required services. Did you call '.AddKubernetesRever

AI-assisted analysis of dotnet/yarp@bd11867bee (2026-08-13). Data as JSON: /api/errors/ebf863fbfeec5c8d. Report an issue: GitHub.