使い方
- インストールコマンドをコピーし、自分の環境へ導入する前にソースを確認します。
- 必要なツール、認証情報、対応環境を原文で確認します。
- 入力と成果物を指定し、出力を資料と照合します。
npx skills add https://github.com/codewithmukesh/dotnet-claude-kit --skill serilog開始前の確認
- 導入にはモデル契約、API枠、ファイルへのアクセス許可は含まれません。
- スター数や導入数は活動の指標であり、独立した品質・安全性試験ではありません。
リポジトリの原文
見出し、例、コード、表、リンク、参照画像を含む原文を表示しています。
Serilog
Core Principles
- Two-stage initialization — Create a bootstrap logger for startup, then replace it with the full logger after DI is ready. This captures startup errors that would otherwise be lost.
- `AddSerilog()` over `UseSerilog()` — Use
builder.Services.AddSerilog()(the modern API) instead ofbuilder.Host.UseSerilog(). It integrates with DI services viaReadFrom.Services(services). - Message templates, not interpolation —
{PropertyName}syntax creates structured data that can be queried. String interpolation ($"...") breaks structure and allocates even when the log level is disabled. - Configure via appsettings.json — Keep log levels, sinks, and overrides in configuration so they can change per environment without redeployment.
Patterns
Two-Stage Bootstrap Setup
csharp
using Serilog;
// Stage 1: Bootstrap logger — captures startup errors before DI
Log.Logger = new LoggerConfiguration()
.MinimumLevel.Override("Microsoft", LogEventLevel.Information)
.Enrich.FromLogContext()
.WriteTo.Console()
.CreateBootstrapLogger();
try
{
Log.Information("Starting application");
var builder = WebApplication.CreateBuilder(args);
// Stage 2: Full logger with DI and configuration
builder.Services.AddSerilog((services, lc) => lc
.ReadFrom.Configuration(builder.Configuration)
.ReadFrom.Services(services)
.Enrich.FromLogContext()
.Enrich.WithMachineName()
.Enrich.WithEnvironmentName()
.Enrich.WithProperty("Application", "MyApp.Api"));
var app = builder.Build();
app.UseSerilogRequestLogging(options =>
{
options.EnrichDiagnosticContext = (diagnosticContext, httpContext) =>
{
diagnosticContext.Set("RequestHost", httpContext.Request.Host.Value);
diagnosticContext.Set("UserAgent",
httpContext.Request.Headers.UserAgent.ToString());
};
});
app.Run();
}
catch (Exception ex)
{
Log.Fatal(ex, "Application terminated unexpectedly");
}
finally
{
await Log.CloseAndFlushAsync();
}appsettings.json Configuration
json
{
"Serilog": {
"MinimumLevel": {
"Default": "Information",
"Override": {
"Microsoft": "Warning",
"Microsoft.AspNetCore": "Warning",
"Microsoft.EntityFrameworkCore": "Warning",
"Microsoft.Hosting.Lifetime": "Information",
"System": "Warning"
}
},
"WriteTo": [
{
"Name": "Console",
"Args": {
"outputTemplate": "[{Timestamp:HH:mm:ss} {Level:u3}] {Message:lj} {Properties:j}{NewLine}{Exception}"
}
},
{
"Name": "File",
"Args": {
"path": "logs/app-.log",
"rollingInterval": "Day",
"retainedFileCountLimit": 30,
"fileSizeLimitBytes": 104857600
}
},
{
"Name": "Seq",
"Args": { "serverUrl": "http://localhost:5341" }
}
],
"Enrich": ["FromLogContext", "WithMachineName", "WithEnvironmentName"],
"Destructure": [
{ "Name": "ToMaximumDepth", "Args": { "maximumDestructuringDepth": 4 } },
{ "Name": "ToMaximumStringLength", "Args": { "maximumStringLength": 1024 } },
{ "Name": "ToMaximumCollectionCount", "Args": { "maximumCollectionCount": 10 } }
]
}
}Override section uses namespace prefixes matched against SourceContext. More specific prefixes take precedence.
Request Logging Middleware
Replaces the multiple per-request log events from ASP.NET Core with a single summary event.
csharp
app.UseSerilogRequestLogging(options =>
{
options.MessageTemplate =
"HTTP {RequestMethod} {RequestPath} responded {StatusCode} in {Elapsed:0.0000} ms";
options.GetLevel = (httpContext, elapsed, ex) => ex is not null
? LogEventLevel.Error
: httpContext.Response.StatusCode >= 500
? LogEventLevel.Error
: LogEventLevel.Information;
options.EnrichDiagnosticContext = (diagnosticContext, httpContext) =>
{
diagnosticContext.Set("UserId",
httpContext.User.FindFirstValue(ClaimTypes.NameIdentifier) ?? "anonymous");
};
});Structured Logging and Destructuring
csharp
// Named properties — creates queryable structured data
logger.LogInformation("Order {OrderId} placed by {CustomerId} for {Total:C}",
orderId, customerId, total);
// @ operator preserves object structure as properties
logger.LogInformation("Processing {@SensorInput}", sensorInput);
// Output: Processing {"Latitude": 25, "Longitude": 134}
// $ operator forces ToString()
logger.LogInformation("Received {$Data}", new[] { 1, 2, 3 });
// Output: Received "System.Int32[]"Scoped Properties with LogContext
csharp
using (LogContext.PushProperty("CorrelationId", correlationId))
using (LogContext.PushProperty("TenantId", tenantId))
{
logger.LogInformation("Processing order {OrderId}", orderId);
// CorrelationId and TenantId attached to ALL log events in this scope
}Requires .Enrich.FromLogContext() on the logger configuration.
OpenTelemetry Sink (OTLP Export)
Export Serilog events directly to any OTLP backend without the OpenTelemetry SDK:
csharp
.WriteTo.OpenTelemetry(options =>
{
options.Endpoint = "http://localhost:4317";
options.Protocol = OtlpProtocol.Grpc;
options.ResourceAttributes = new Dictionary<string, object>
{
["service.name"] = "MyApp.Api",
["deployment.environment"] = "production"
};
})Serilog.Expressions for Filtering
Requires the Serilog.Expressions package.
csharp
// Exclude health check noise
.Filter.ByExcluding("RequestPath like '/health%'")
// Route errors to a separate file
.WriteTo.Conditional("@l = 'Error'",
wt => wt.File("logs/errors-.log", rollingInterval: RollingInterval.Day))[LoggerMessage] Source Generator for Hot Paths
Built into Microsoft.Extensions.Logging.Abstractions — compile-time generated, zero allocations when the level is disabled.
csharp
public static partial class OrderLogs
{
[LoggerMessage(Level = LogLevel.Information,
Message = "Order {OrderId} created for {CustomerId}")]
public static partial void OrderCreated(this ILogger logger, Guid orderId, Guid customerId);
}
// Usage
logger.OrderCreated(order.Id, order.CustomerId);Anti-patterns
Don't Use String Interpolation
csharp
// BAD — breaks structured logging, allocates even when level is disabled
logger.LogInformation($"Order {orderId} created for {customerId}");
// GOOD — message template with named parameters
logger.LogInformation("Order {OrderId} created for {CustomerId}", orderId, customerId);Don't Skip CloseAndFlush
csharp
// BAD — async sinks (Seq, OTLP, Elasticsearch) lose buffered events
app.Run();
// GOOD — wrap in try/finally
try { app.Run(); }
catch (Exception ex) { Log.Fatal(ex, "Unhandled exception"); }
finally { await Log.CloseAndFlushAsync(); }Don't Log Sensitive Data
csharp
// BAD — passwords and tokens in logs
logger.LogInformation("Login: {Email} with password {Password}", email, password);
// GOOD — never log secrets, passwords, tokens, or PII
logger.LogInformation("Login: {Email}", email);Don't Destructure Without Limits
csharp
// BAD — large object graphs cause memory issues and massive log entries
logger.LogInformation("Request: {@Request}", httpContext.Request);
// GOOD — configure destructuring limits
.Destructure.ToMaximumDepth(4)
.Destructure.ToMaximumStringLength(1024)
.Destructure.ToMaximumCollectionCount(10)
// BETTER — destructure to specific properties
.Destructure.ByTransforming<HttpRequest>(r => new { r.Method, r.Path })Don't Use the Deprecated Elasticsearch Sink
csharp
// BAD — the Serilog.Sinks.Elasticsearch PACKAGE is deprecated
// <PackageReference Include="Serilog.Sinks.Elasticsearch" />
.WriteTo.Elasticsearch("http://localhost:9200")
// GOOD — same method name, but from the official Elastic.Serilog.Sinks
// package, which writes ECS-formatted documents to data streams
// <PackageReference Include="Elastic.Serilog.Sinks" />
.WriteTo.Elasticsearch([new Uri("https://elastic.example.com:9200")], opts =>
opts.DataStream = new DataStreamName("logs", "myapp"))Decision Guide
| Scenario | Recommendation |
|---|---|
| Application logging | Serilog with AddSerilog() and appsettings.json |
| Log storage (development) | Seq (free single-user) or Aspire Dashboard |
| Log storage (production) | Seq, Elasticsearch (Elastic sink), or OTLP backend |
| Request logging | UseSerilogRequestLogging() (replaces per-request noise) |
| Scoped properties | LogContext.PushProperty() in middleware |
| Log filtering | Serilog.Expressions for expression-based filtering |
| High-performance paths | [LoggerMessage] source generator |
| Audit trails | AuditTo (synchronous, exceptions propagate) |
| Log levels by environment | MinimumLevel.Override per namespace in appsettings |
| OpenTelemetry integration | Serilog.Sinks.OpenTelemetry (no SDK dependency) |
