Troubleshoot IIS - Service Not Available 503 Issue

Table of Contents

1. Introduction
2. Useful Resources
3. Conclusion

Introduction

When working with IIS, you may encounter the "Service Unavailable 503" error. This usually occurs when the application pool stops automatically. The following is a collection of useful resources for troubleshooting this issue.

Useful Resources

• https://www.google.com/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#safe=active&q=mvc+site+iis+stopped

• http://www.codeproject.com/Questions/674073/Csharp-Code-to-Start-and-stop-perticular-applicati

• https://social.msdn.microsoft.com/Forums/vstudio/en-US/b1cdd1be-1a02-497d-946f-b0f211c21980/restart-iis-application-pool-using-c?forum=csharpgeneral

• http://stackoverflow.com/questions/14359983/asp-net-mvc-site-has-stopped-working-in-iis7

• http://stackoverflow.com/questions/18016353/why-does-the-application-pool-automatically-stop

• http://weblogs.asp.net/scottgu/auto-start-asp-net-applications-vs-2010-and-net-4-0-series

• https://www.google.com/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=how+to+crash+asp.net+mvc+app&safe=active&start=30

• http://stackoverflow.com/questions/23615050/random-crashes-in-asp-net-mvc-how-to-debug

• http://forums.asp.net/t/2065560.aspx?Thread+Abort+in+ASP+NET+app+causes+w3wp+exe+to+crash

• http://w3stack.org/question/why-c-wrapper-of-c-crash-crashes-web-app-but-runs-fine-as-console-app/

• https://blogs.msdn.microsoft.com/asiatech/2009/12/23/net-application-may-crash-when-calling-function-from-native-c-dll/

• https://msdn.microsoft.com/en-us/library/system.appdomain.unhandledexception(v=VS.90).aspx

• https://raygun.io/net/dotnet-crash-handling

• http://stackoverflow.com/questions/2481047/executing-code-on-application-crash

• https://blog.kowalczyk.info/article/c4qb/How-to-make-software-crash-less.html

• https://www.google.com/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=iis%20application%20pool%20stopped

• http://www.codeproject.com/Questions/283255/Application-Pool-Stops-automatically

• http://stackoverflow.com/questions/18016353/why-does-the-application-pool-automatically-stop

• https://forums.iis.net/t/1191046.aspx

Conclusion

The IIS 503 Service Unavailable error is commonly caused by an application pool that has stopped. The resources above cover various scenarios including automatic pool stopping, unhandled exceptions crashing the worker process, and strategies for keeping ASP.NET applications running reliably.