REST API random 404 error when a server is down on load balancer

Question

We have a REST based API project. The project is hosted in IIS on multiple servers on a load balancer.It works great except when a server goes down on the load balancer, we receive a 404 Bad Request error for few seconds and then it resolves itself. How do we resolve this? Are there any changes that need to be done in IIS or on the REST API project itself?

Answer 1

As far as I know, if you use IIS ARR's loadbalance there is no need to add the specail setting to check the server's status. The IIS ARR healthy test will auto send the request to check the server is work well or not. If the IIS ARR find the server is down or return error, it will not redirect the request to the server.

Besides, as far as I know, the 404 error means the page not found not the bad request. Normally, 400 is the bad request status code.

If you find a server is down in your server farms, I suggest you could try to access the server directly through the brwoser to know the details error message.

If the server return 404 error, that means your browser couldn't access the server, it is a network issue normally. You should check the DNS server setting or make sure the IIS web application is running.

If the server return 400 error, you should troublshooting according to the details 400 error message. Normall, it shows when the request contains the wrong header.