What causes azure websites to ignore settings from web.config?

Question

My web.config contains multiple entries in "appSettings" (e.g.: twilio account key). One of these is for the asp.net chart control. It's the configuration part that states where the images the control generates are to be stored.

All of these settings work on my development machine. That is, i can connect to twilio and the chart control stores image in memory (as it should, according to the settings).

When i publish the site to my azure website (using vs), all of the settings work, apart from the chart control one. The chart control behaves as if the setting isn't even there. (it defaults to c:\TempImageFiles for storage).

I looked into the published version of the web.config and the setting is there. Only, it's beeing ignored.

My next attempt was to add that setting using the portal. (It's possible to add appSettings for a web app using the portal). I copied the exact same setting from web.config into the portal settings. This worked, so there is nothing wrong with what's in the settings.

So my question is: Why are some (at least this one) settings from web.config ignored when the app runs inside an azure web app?

Answer 1

You might have an app setting defined in the Web App's configuration with an identical name that overrides the web.config setting. This is typically done to have production settings stored in Azure instead of Web.config.

You can confirm if this is the case by opening your Web App's blade in the new portal, and checking the Application Settings tab there.

Answer 2

azure websites / azure web app service are typical web applications running on top of azure PaaS infrastructure. So whatever storage allocated to the service is accessible from the app. But it cannot be the typical C: or D: where in a regular server the app may have complete access. Mostly the C: space is allocated for IIS hosting. D:\local is something you can utilize as the app will have complete read and write access.

Please refer azure web app service sandbox details here.

If you are accessing the path via code try using Server.MapPath property to get access to the path. options like Path.GetTempPath() will not work.

One point to note is, any local storage in azure PaaS services is to be treated like a temporary storage. Whenever the site, service or role recycles the storage will be gone a fresh storage will be assigned.