Asp Net Core 3 Sample with 503 Service Unavailable - asp.net-core

Question

When creating a new ASP.NET Core Web Application using react and .Net Core 3.0 or 3.1 in visual studio and run the application the page shows:
503 Service Unavailable
Failed to connect to server localhost
I am using windows 10 professional and visual studio 2019.
The error happens running in IISExpress and kestrel.
On a different machine this works fine.
Creating a template using "Web Application (Model-View-Controller)" works.
The api call works (https://localhost:5001/WeatherForecast).
I'm troubleshooting a migration in a project from AspNet Core 2.2 to 3.0 with the same error, I checked to see if the template project would work and found out that the error was not specific to the migration. Figuring out why the template is not working will probably solve the error with the migration.
Edit:
Disabling firewall did not solve issue.
Here is the debug log for trying to open the page:
dbug: Microsoft.AspNetCore.Server.Kestrel[39]
Connection id "0HLTKHV201G3Q" accepted.
dbug: Microsoft.AspNetCore.Server.Kestrel[1]
Connection id "0HLTKHV201G3Q" started.
dbug: Microsoft.AspNetCore.Server.Kestrel[39]
Connection id "0HLTKHV201G3R" accepted.
info: Microsoft.AspNetCore.Hosting.Diagnostics[1]
Request starting HTTP/1.1 GET http://localhost:5000/
dbug: Microsoft.AspNetCore.Server.Kestrel[1]
Connection id "0HLTKHV201G3R" started.
trce: Microsoft.AspNetCore.HostFiltering.HostFilteringMiddleware[2]
All hosts are allowed.
dbug: Microsoft.AspNetCore.StaticFiles.StaticFileMiddleware[4]
The request path / does not match a supported file type
dbug: Microsoft.AspNetCore.Routing.Matching.DfaMatcher[1000]
No candidates found for the request path '/'
dbug: Microsoft.AspNetCore.Routing.EndpointRoutingMiddleware[2]
Request did not match any endpoints
info: Microsoft.AspNetCore.Hosting.Diagnostics[2]
Request finished in 27.156ms 503 text/html; charset=UTF-8
dbug: Microsoft.AspNetCore.Server.Kestrel[10]
Connection id "0HLTKHV201G3Q" disconnecting.
dbug: Microsoft.AspNetCore.Server.Kestrel[2]
Connection id "0HLTKHV201G3Q" stopped.
dbug: Microsoft.AspNetCore.Server.Kestrel.Transport.Sockets[6]
Connection id "0HLTKHV201G3Q" received FIN.
dbug: Microsoft.AspNetCore.Server.Kestrel.Transport.Sockets[7]
Connection id "0HLTKHV201G3Q" sending FIN because: "The Socket transport's send loop completed gracefully."
info: Microsoft.AspNetCore.Hosting.Diagnostics[1]
Request starting HTTP/1.1 GET http://localhost:5000/favicon.ico
trce: Microsoft.AspNetCore.HostFiltering.HostFilteringMiddleware[2]
All hosts are allowed.
dbug: Microsoft.AspNetCore.StaticFiles.StaticFileMiddleware[5]
The request path /favicon.ico does not match an existing file
dbug: Microsoft.AspNetCore.Routing.Matching.DfaMatcher[1000]
No candidates found for the request path '/favicon.ico'
dbug: Microsoft.AspNetCore.Routing.EndpointRoutingMiddleware[2]
Request did not match any endpoints
info: Microsoft.AspNetCore.Hosting.Diagnostics[2]
Request finished in 19.8075ms 503 text/html; charset=UTF-8
dbug: Microsoft.AspNetCore.Server.Kestrel.Transport.Sockets[6]
Connection id "0HLTKHV201G3R" received FIN.
dbug: Microsoft.AspNetCore.Server.Kestrel[10]
Connection id "0HLTKHV201G3R" disconnecting.
dbug: Microsoft.AspNetCore.Server.Kestrel.Transport.Sockets[7]
Connection id "0HLTKHV201G3R" sending FIN because: "The client closed the connection."
dbug: Microsoft.AspNetCore.Server.Kestrel[2]
Connection id "0HLTKHV201G3R" stopped.

Answer 1

This was happening because proxy was blocking requests from .Net Host to react and angular.
In AspNetCore 3.0 HttpClient now has a default proxy created from system variables HTTPS_PROXY, HTTP_PROXY and NO_PROXY.
Adding NO_PROXY=localhost to system variables solved my problem.