feat(health): IActiveNodeGate seam + RequireActiveNode filter

2026-06-01 06:43:11 -04:00
parent d1b837e718
commit 5b82d68ea9
3 changed files with 152 additions and 0 deletions
@@ -0,0 +1,62 @@
+using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.Http;
+using Microsoft.Extensions.DependencyInjection;
+
+namespace ZB.MOM.WW.Health;
+
+/// <summary>
+/// Endpoint filter that gates a route to the active node. Resolves <see cref="IActiveNodeGate"/>
+/// from request services; when it is registered and reports a standby
+/// (<see cref="IActiveNodeGate.IsActiveNode"/> is <c>false</c>) the request is short-circuited with
+/// HTTP 503 and a <c>Retry-After</c> header. When no gate is registered (non-clustered host / tests)
+/// the request is served, preserving prior behaviour.
+/// </summary>
+public sealed class ActiveNodeGateEndpointFilter : IEndpointFilter
+{
+    /// <summary>Default <c>Retry-After</c> value (seconds) advertised on a standby 503 response.</summary>
+    private const int RetryAfterSeconds = 5;
+
+    /// <summary>
+    /// Returns 503 (with <c>Retry-After</c>) when the resolved <see cref="IActiveNodeGate"/> reports
+    /// a standby node; otherwise delegates to the next filter or endpoint handler.
+    /// </summary>
+    /// <param name="context">The endpoint filter invocation context.</param>
+    /// <param name="next">The next filter or endpoint handler in the pipeline.</param>
+    public async ValueTask<object?> InvokeAsync(
+        EndpointFilterInvocationContext context,
+        EndpointFilterDelegate next)
+    {
+        ArgumentNullException.ThrowIfNull(context);
+        ArgumentNullException.ThrowIfNull(next);
+
+        var httpContext = context.HttpContext;
+        var gate = httpContext.RequestServices.GetService<IActiveNodeGate>();
+
+        if (gate is { IsActiveNode: false })
+        {
+            httpContext.Response.Headers.RetryAfter = RetryAfterSeconds.ToString();
+            return Results.StatusCode(StatusCodes.Status503ServiceUnavailable);
+        }
+
+        return await next(context);
+    }
+}
+
+/// <summary>
+/// Route convention that gates endpoint(s) to the active node, returning 503 on standby nodes.
+/// </summary>
+public static class ActiveNodeGateExtensions
+{
+    /// <summary>
+    /// Applies <see cref="ActiveNodeGateEndpointFilter"/> to the decorated endpoint(s): the route is
+    /// served only when the DI-resolved <see cref="IActiveNodeGate"/> reports the node active, and
+    /// returns 503 with a <c>Retry-After</c> header when the node is a standby.
+    /// </summary>
+    /// <param name="builder">The endpoint convention builder to decorate.</param>
+    /// <returns>The same <paramref name="builder"/> for chaining.</returns>
+    public static IEndpointConventionBuilder RequireActiveNode(this IEndpointConventionBuilder builder)
+    {
+        ArgumentNullException.ThrowIfNull(builder);
+        return builder.AddEndpointFilter(new ActiveNodeGateEndpointFilter());
+    }
+}
@@ -0,0 +1,20 @@
+namespace ZB.MOM.WW.Health;
+
+/// <summary>
+/// Single-property seam: is this node the active / leader node?
+/// </summary>
+/// <remarks>
+/// Attach to endpoints or route groups via
+/// <see cref="ActiveNodeGateExtensions.RequireActiveNode"/>. A standby node must not serve the
+/// gated routes, so the filter returns HTTP 503 when <see cref="IsActiveNode"/> is <c>false</c>.
+/// The implementation is supplied by the consumer — the <c>ZB.MOM.WW.Health.Akka</c> package ships
+/// <c>AkkaActiveNodeGate</c> for clustered nodes; non-Akka hosts provide their own.
+/// </remarks>
+public interface IActiveNodeGate
+{
+    /// <summary>
+    /// <c>true</c> when this node is the active node and may serve gated routes;
+    /// <c>false</c> on a standby node.
+    /// </summary>
+    bool IsActiveNode { get; }
+}