How to fix ‘HTTP Error 503. The service is unavailable’ in Windows?

Cause 

In Windows Hosting, this error occurs when an application pool for a particular website is stopped or crashes when the website exceeds the allocated private memory limit.

All websites hosted under our Windows Shared server have their own dedicated application pool. These application pools usually hold 250 MB of private memory; for example, in the Beginner ++ plan, you will get 250 MB. (This memory increases as per the plan you select) So, in that case, your web application can use a maximum of 250 MB of private memory.

If any web page/request demands more than 250 MB of private memory, your website's application pool will get stopped/crashed, and your website will throw HTTP Error 503. This event will be logged in the Web server logs.

Fix

This error can be fixed by manually starting the application pool from IIS. However, while you have purchased the Windows Shared Hosting, you won't have IIS access. Hence, you can contact us via live chat or support ticket if you face this error. 

After starting the application pool, you may face this error again if the same web request comes (that caused the application pool to crash previously). Hence, rather than fixing it each time you receive this error, we will send you the exact exception that caused the application pool to crash so that you can fix your code to prevent its recurrence.

However, we offer different dedicated application pool RAM in windows shared hosting plans, 

If your web application is heavy and it demands more private memory, then you should consider purchasing additional application pool private memory. An additional 250 MB of private memory will cost you $5/ Month, which you can purchase by contacting us through the Helpdesk.