Added Serilog logging, added Elmah error logging, added health checks

src/Indexer/IndexerHealthChecks.cs

@@ -0,0 +1,44 @@
+using System.Collections.ObjectModel;
+using Indexer.Models;
+using Microsoft.Extensions.Diagnostics.HealthChecks;
+
+namespace Indexer;
+
+public class WorkerHealthCheck : IHealthCheck
+{
+    private readonly WorkerCollection _workerCollection;
+    public WorkerHealthCheck(WorkerCollection workerCollection)
+    {
+        _workerCollection = workerCollection;
+    }
+    public Task<HealthCheckResult> CheckHealthAsync(
+        HealthCheckContext context, CancellationToken cancellationToken = default)
+    {
+        bool hasDegraded = false;
+        bool hasUnhealthy = false;
+        Dictionary<string, HealthStatus> degradedWorkerList = [];
+        foreach (Worker worker in _workerCollection.Workers)
+        {
+            HealthCheckResult workerHealth = worker.HealthCheck();
+            hasDegraded |= workerHealth.Status == HealthStatus.Degraded;
+            hasUnhealthy |= workerHealth.Status == HealthStatus.Unhealthy;
+            if (workerHealth.Status != HealthStatus.Healthy)
+            {
+                degradedWorkerList[worker.Name] = workerHealth.Status;
+            }
+        }
+        string degradedWorkerListString = "{" + string.Join(",", [.. degradedWorkerList.Select(kv => '"' + kv.Key + "\": " + kv.Value)]) + "}";
+        if (hasUnhealthy)
+        {
+            return Task.FromResult(
+                HealthCheckResult.Unhealthy(degradedWorkerListString));
+        }
+        else if (hasDegraded)
+        {
+            return Task.FromResult(
+                HealthCheckResult.Degraded(degradedWorkerListString));
+        }
+        return Task.FromResult(
+                HealthCheckResult.Healthy());
+    }
+}