API returns status 200 but empty body after IIS restart or Idle time

Question

I have a .Net core 8 webapi project. it works fine normally. but when it is called after a long idle time or after the iisrestart, returns 200 and the response body is empty.
I tried to log the data, and there is data in the log. don't know what is happening after the return.
did below for app pool
Start Mode to AlwaysRunning.
Idle Time-out to 0

Answer 1

1. First, ensure proper startup configuration by adding Application Initialization in your web.config:

      <system.webServer>
          <applicationInitialization>
              <add initializationPage="/" hostName="localhost" />
          </applicationInitialization>
      </system.webServer>
   

2. In your Program.cs or Startup.cs, make sure JSON serialization is properly configured:

builder.Services.AddControllers()
    .AddJsonOptions(options =>
    {
        options.JsonSerializerOptions.PropertyNameCaseInsensitive = true;
        options.JsonSerializerOptions.PropertyNamingPolicy = null;
    });

1. Add response compression and configure it:

      builder.Services.AddResponseCompression(options =>
      {
          options.EnableForHttps = true;
      });
      // In Configure method or middleware pipeline
      app.UseResponseCompression();
   

2. Implement a warmup middleware:

      public class WarmupMiddleware
      {
          private readonly RequestDelegate _next;
          public WarmupMiddleware(RequestDelegate next)
          {
              _next = next;
          }
          public async Task InvokeAsync(HttpContext context)
          {
              // Ensure JsonSerializer is initialized
              JsonSerializer.Serialize(new { });
              
              await _next(context);
          }
      }
      // Register in Program.cs
      app.UseMiddleware<WarmupMiddleware>();
   

3. Check if you're using async/await correctly in your controllers:

      [ApiController]
      [Route("[controller]")]
      public class YourController : ControllerBase
      {
          [HttpGet]
          public async Task<ActionResult<YourModel>> Get()
          {
              var result = await _service.GetDataAsync();
              
              // Explicitly serialize to ensure proper response
              var json = JsonSerializer.Serialize(result);
              return Content(json, "application/json");
          }
      }
   

4. Configure IIS Application Pool advanced settings:

• Set "Idle Time-out Action" to "Suspend"
• Enable "Preload Enabled"
• Set "Start Mode" to "AlwaysRunning"
• Configure IIS Application Pool advanced settings:
• Set "Idle Time-out Action" to "Suspend"
• Enable "Preload Enabled"
  • Set "Start Mode" to "AlwaysRunning"