propagate shared-config and library-option changes between instances

Add a Redis pub/sub invalidation bus, publish from the configuration and library-option write paths, and drop the matching local cache entry on the instances that did not write. No-op without a Redis connection string, and fails open when it is unreachable.
2026-09-20 23:47:21 +10:00
parent ec581b5e5f
commit b662ffa48f
16 changed files with 919 additions and 1 deletions
@@ -0,0 +1,74 @@
+using System;
+using Emby.Server.Implementations.Configuration;
+using MediaBrowser.Common.Configuration;
+using MediaBrowser.Controller.MediaEncoding;
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Logging;
+using StackExchange.Redis;
+
+namespace Jellyfin.Server.Extensions;
+
+/// <summary>
+/// Extensions for registering the shared-configuration invalidation bus.
+/// </summary>
+public static class ConfigurationInvalidationServiceCollectionExtensions
+{
+    /// <summary>
+    /// Registers the invalidation bus, Redis-backed when a connection string is configured and no-op
+    /// otherwise, and the subscriber applying the notices other instances publish.
+    /// </summary>
+    /// <remarks>
+    /// The connection string is only set for a multi-instance deployment, which is the only shape where
+    /// one instance can write the shared configuration directory behind another's back.
+    /// </remarks>
+    /// <param name="serviceCollection">The service collection.</param>
+    /// <param name="configuration">The configuration to read the Redis connection string from.</param>
+    /// <param name="logger">The logger to report the selected bus on.</param>
+    /// <returns>The updated service collection.</returns>
+    public static IServiceCollection AddConfigurationInvalidationBus(
+        this IServiceCollection serviceCollection,
+        IConfiguration configuration,
+        ILogger logger)
+    {
+        ArgumentNullException.ThrowIfNull(configuration);
+        ArgumentNullException.ThrowIfNull(logger);
+
+        if (string.IsNullOrEmpty(configuration[TranscodeStoreOptions.RedisConnectionStringKey]))
+        {
+            logger.LogInformation(
+                "Configuration invalidation bus: {Bus}. Shared-configuration and library-visibility changes stay local to the instance that made them; set {Key} to propagate them.",
+                nameof(NullConfigurationInvalidationBus),
+                TranscodeStoreOptions.RedisConnectionStringKey);
+
+            return serviceCollection.AddSingleton<IConfigurationInvalidationBus>(NullConfigurationInvalidationBus.Instance);
+        }
+
+        logger.LogInformation(
+            "Configuration invalidation bus: {Bus}. Shared-configuration and library-visibility changes propagate to every instance.",
+            nameof(RedisConfigurationInvalidationBus));
+
+        serviceCollection.AddSingleton<IConfigurationInvalidationBus>(sp =>
+        {
+            try
+            {
+                return new RedisConfigurationInvalidationBus(
+                    sp.GetRequiredService<IConnectionMultiplexer>(),
+                    sp.GetRequiredService<ILogger<RedisConfigurationInvalidationBus>>());
+            }
+            catch (Exception ex)
+            {
+                // Fail open: an unreachable Redis degrades to the single-instance behaviour of every
+                // instance keeping its own cached configuration, rather than aborting startup.
+                sp.GetRequiredService<ILogger<CoreAppHost>>().LogError(
+                    ex,
+                    "Redis is configured but unavailable, so shared-configuration changes will not propagate between instances. Check {Key}.",
+                    TranscodeStoreOptions.RedisConnectionStringKey);
+
+                return NullConfigurationInvalidationBus.Instance;
+            }
+        });
+
+        return serviceCollection.AddHostedService<ConfigurationInvalidationSubscriber>();
+    }
+}