Background and Architectural Context

Nancy's design embraces low ceremony and modularity. While this is a strength for small services, in enterprise ecosystems it can introduce complexity. Services often host multiple Nancy modules loaded dynamically, combined with custom bootstrapper configurations and external dependency injection containers (e.g., Autofac, Ninject). Improper lifecycle scoping or disposal can lead to retained request contexts, excessive GC pressure, and degraded throughput under load.

Common Architectural Triggers

• Long-lived singleton services holding references to request-specific objects
• Improper disposal of INancyContext after request completion
• Pipeline hooks creating closure captures that retain large object graphs
• Dynamic module assembly loading without explicit unloading in plugin-like architectures

Diagnostic Approach

Performance Profiling

Use profilers such as JetBrains dotTrace or PerfView to identify hotspots in pipeline execution. Look for handlers that allocate large collections or repeatedly serialize heavy objects.

// Example: Tracking pipeline stage execution time
pipelines.BeforeRequest += ctx => {
    var sw = Stopwatch.StartNew();
    ctx.Items["_start"] = sw;
    return null;
};

pipelines.AfterRequest += ctx => {
    var sw = (Stopwatch)ctx.Items["_start"];
    sw.Stop();
    Console.WriteLine($"Request took {sw.ElapsedMilliseconds}ms");
};

Memory Leak Investigation

Capture memory dumps with dotnet-dump or Visual Studio Diagnostic Tools. Check for NancyContext instances in the heap that persist beyond expected scope, and trace references to static caches or long-lived delegates.

Common Pitfalls and Misconceptions

• Assuming garbage collection will clean up all request data: Without explicit disposal, closures and static event handlers can hold references indefinitely.
• Mixing singleton and per-request lifecycles incorrectly: Leads to memory growth and thread safety hazards.
• Relying on default bootstrapper for complex DI scenarios: Can cause misaligned scopes with advanced containers.

Step-by-Step Resolution

1. Enforce Proper Context Disposal

pipelines.AfterRequest += ctx => {
    (ctx as IDisposable)?.Dispose();
};

2. Align DI Container Scopes

Configure the container to bind per-request services correctly. For Autofac:

builder.RegisterType<MyService>().InstancePerLifetimeScope();

3. Prevent Closure-Based Retention

Refactor pipeline hooks to avoid capturing request-specific objects in static or long-lived delegates.

4. Manage Dynamic Assembly Loading

When loading modules dynamically, use AssemblyLoadContext and unload when modules are no longer needed, particularly in plugin-based Nancy hosts.

Best Practices for Long-Term Stability

• Audit pipeline hooks quarterly to remove unnecessary allocations.
• Integrate memory leak detection into staging performance tests.
• Explicitly configure DI scope rules for each service.
• Log request lifecycle timings to proactively spot degradation trends.

Conclusion

Nancy's lightweight architecture makes it attractive for microservices and APIs, but unchecked lifecycle management and request pipeline complexity can degrade performance over time. By tightening DI scope control, avoiding closure leaks, and enforcing proper context disposal, architects can keep Nancy services lean and responsive, even under sustained enterprise workloads.

FAQs

1. How do I detect context leaks in Nancy?

Use memory profiling tools to identify NancyContext instances surviving GC. Trace references to static fields or global event handlers.

2. Should I always use a custom bootstrapper?

For simple apps, the default is fine. For enterprise workloads with complex DI, a custom bootstrapper offers better lifecycle control.

3. Can dynamic assembly loading be safe in Nancy?

Yes, but ensure you unload unused assemblies via AssemblyLoadContext to prevent memory bloat.

4. Is per-request DI scope necessary?

In most cases, yes. It ensures resources tied to a request are released promptly after completion.

5. How can I measure pipeline performance in production?

Insert lightweight timing code in BeforeRequest/AfterRequest hooks and log metrics to a centralized system like Application Insights.