Episerver page gives 404

Short blog post about an issue I just encountered.

Scenario:

The site works great. After implementing some new functionality (a new page type with a header in our case), the start page just suddenly stops working and responds with 404. Episerver edit mode still works however. What just happened and how to solve it?

Solution:

1. Turn on full logging to get information about routing and details around that.
   
   
2. Logs gives this:
   2021-02-09 15:30:54,085 [43] DEBUG EPiServer.Web.Routing.Segments.Internal.NodeSegment: Url 'https://dev.customerweb.local/' was routed to content with id '5' and language was set to 'sv'
   2021-02-09 15:30:54,085 [43] TRACE EPiServer.Framework.Cache.ObjectInstanceCacheExtensions: Trying to Read the cacheKey = 'EP:LanguageBranch'
   2021-02-09 15:30:54,085 [43] TRACE EPiServer.Framework.Cache.ObjectInstanceCacheExtensions: Trying to Read the cacheKey = 'EP:LanguageBranch'
   2021-02-09 15:30:54,085 [43] TRACE EPiServer.Framework.Cache.ObjectInstanceCacheExtensions: Trying to Read the cacheKey = 'EPPageData:5'
   2021-02-09 15:30:54,085 [43] TRACE EPiServer.Framework.Cache.ObjectInstanceCacheExtensions: Trying to Read the cacheKey = 'EPPageData:5:sv'
   2021-02-09 15:30:54,085 [43] TRACE EPiServer.Framework.Cache.ObjectInstanceCacheExtensions: Trying to Read the cacheKey = 'EPPageData:5'
   2021-02-09 15:30:54,086 [43] DEBUG EPiServer.Web.TemplateResolver: StartPage: Selected CustomerName.Web.Features.SiteLayout.header.HeaderController. (tag='', channel='', category='MvcController')
   2021-02-09 15:30:54,063 [134] ERROR EPiServer.Global: Unhandled exception in ASP.NET
   System.Web.HttpException (0x80004005): The file '/link/43F936C99B234EA397B261C538AD07C9.aspx' does not exist.
3. The first line in log tells you that Episerver was successful in routing to the correct content, it has id 5 and also the language 'sv'. Yey! So far so good!
4. The debug line before the error however
   TemplateResolver: StartPage: Selected CustomerName.Web.Features.SiteLayout.header.HeaderController
   Wuuut?! It's trying to use the new HeaderController to render the page with!? Aha!
5. The newly developed HeaderController looks like this:
   

   public class HeaderController : PageController<SitePageData>

   Unfortunately the controller that renders the startpage looks like this:
   

   public class DefaultPageController : PageController<SitePageData>

   So what happens is that Episerver gets confused what controller it should use to render the startpage. Earlier it used the DefaultsPageController and everything was fine but now with the new HeaderController, it selected that one instead. This is also visible in the logs 
   TemplateResolver: StartPage: Selected CustomerName.Web.Features.SiteLayout.header.HeaderController
   
6. Solution: Make the controllers more specific to avoid letting Episervers TemplateResolver guess. The short story is to be careful when using common parent classes like SitePageData in our case. It's a bad idea to have two controllers handling that. There is a nice detailed guide here:
   https://world.episerver.com/documentation/developer-guides/CMS/rendering/selecting-templates/ 

Hope that helps someone googling 404 issues with Episerver. Check your logs and check that it's the right controller that is assigned to handle the call to your content or you can get funny issues. 

Happy coding!