microsoft/aspire · error · DistributedApplicationException

Could not create HTTP command for resource

Error message

Could not create HTTP command for resource '{builder.Resource.Name}' as the endpoint selector returned null.

What it means

HTTP resource commands (e.g. start/stop-style commands over HTTP) obtain their target endpoint by invoking a user-supplied or default endpoint selector. If the selector returns null there is no endpoint to send the request to, so Aspire throws DistributedApplicationException naming the resource.

Solutions

Add or verify the resource declares an endpoint (WithEndpoint/WithHttpEndpoint) before the HTTP command is created
Fix the custom selector so it returns an endpoint reference instead of null (check name/scheme filters)
Add a fallback in the selector, e.g. endpoints.FirstOrDefault(e => e.Scheme == "http") ?? endpoints.First()

Example fix

// before
selector: () => endpoints.FirstOrDefault(e => e.EndpointName == "https") // null when only http exists
// after
selector: () => endpoints.FirstOrDefault(e => e.EndpointName == "https")
       ?? endpoints.First(e => e.Scheme == "http");

Defensive patterns

Strategy: type-guard

Validate before calling

var endpoints = builder.Resource.GetEndpoints().ToList();
if (endpoints.Count == 0) throw new InvalidOperationException("Resource has no endpoints for HTTP command");

Type guard

bool SelectorResolves(Func<EndpointReference?> selector) => selector() is not null;

Try / catch

try { builder.WithHttpCommand(...); }
catch (DistributedApplicationException ex) when (ex.Message.Contains("endpoint selector returned null")) { /* fix selector or add endpoint */ }

Prevention

Make custom endpoint selectors always fall back to a default endpoint
Declare endpoints before creating HTTP commands that reference them

When it happens

Trigger: Passing a custom HttpCommandOptions.EndpointSelector (or equivalent selector parameter) whose function returns null — e.g. it filters endpoints by scheme/name and no endpoint matches; calling the API before the resource has any endpoint annotations.

Common situations: Selector logic that assumes an endpoint named 'https' exists when only 'http' is defined; endpoints added conditionally so they are missing in some run modes; running the command on a resource that never got an WithEndpoint call.

Related errors

AI-assisted analysis of microsoft/aspire@25830f84bd (2026-09-16). Data as JSON: /api/errors/bd6a15b43c9d5e4b. Report an issue: GitHub.

Appendix: source

Thrown at src/Aspire.Hosting/ResourceBuilderExtensions.cs:3684

    /// loadGenerator.WithReference(customerService);
    /// </code>
    /// </example>
    /// <para>This method is not available in polyglot app hosts.</para>
    /// </remarks>
    [AspireExportIgnore(Reason = "Use the ATS-specific withHttpCommand export.")]
    public static IResourceBuilder<TResource> WithHttpCommand<TResource>(
        this IResourceBuilder<TResource> builder,
        string path,
        string displayName,
        Func<EndpointReference>? endpointSelector,
        string? commandName = null,
        HttpCommandOptions? commandOptions = null)
        where TResource : IResourceWithEndpoints
    {
        endpointSelector ??= DefaultEndpointSelector(builder);

        var endpoint = endpointSelector()
            ?? throw new DistributedApplicationException($"Could not create HTTP command for resource '{builder.Resource.Name}' as the endpoint selector returned null.");

        if (endpoint.Scheme != "http" && endpoint.Scheme != "https")
        {
            throw new DistributedApplicationException($"Could not create HTTP command for resource '{builder.Resource.Name}' as the endpoint with name '{endpoint.EndpointName}' and scheme '{endpoint.Scheme}' is not an HTTP endpoint.");
        }

        builder.ApplicationBuilder.Services.AddHttpClient();

        commandOptions ??= HttpCommandOptions.Default;
        commandOptions.Method ??= HttpMethod.Post;

        commandName ??= $"{endpoint.Resource.Name}-{endpoint.EndpointName}-http-{commandOptions.Method.Method.ToLowerInvariant()}-{path}";

        if (commandOptions.UpdateState is null)
        {
            commandOptions.UpdateState = context =>
            {
                var resourceState = context.ResourceSnapshot.State?.Text;

View on GitHub (pinned to 25830f84bd)