Kestrel permission denied for non-root user - asp.net

Question

I have a dotnet application, which is not working as non-root user even though I am exposing it on port 5000, greater then the 1024 requirement.
WORKDIR /app
EXPOSE 5000
COPY app $local_artifact_path
RUN chown www-data:www-data /app /app/*
RUN chmod 777 /app
USER www-data
ENTRYPOINT dotnet $app_entry_point
The stacktrace is
warn: Microsoft.AspNetCore.DataProtection.Repositories.EphemeralXmlRepository[50]
Using an in-memory repository. Keys will not be persisted to storage.
warn: Microsoft.AspNetCore.DataProtection.KeyManagement.XmlKeyManager[59]
Neither user profile nor HKLM registry available. Using an ephemeral key repository. Protected data will be unavailable when application exits.
warn: Microsoft.AspNetCore.DataProtection.KeyManagement.XmlKeyManager[35]
No XML encryptor configured. Key {551dd8d6-67f6-4c6a-b5a4-9ea86b69593b} may be persisted to storage in unencrypted form.
crit: Microsoft.AspNetCore.Server.Kestrel[0]
Unable to start Kestrel.
System.Net.Sockets.SocketException (13): Permission denied
at System.Net.Sockets.Socket.UpdateStatusAfterSocketErrorAndThrowException(SocketError error, String callerName)
at System.Net.Sockets.Socket.DoBind(EndPoint endPointSnapshot, SocketAddress socketAddress)
at System.Net.Sockets.Socket.Bind(EndPoint localEP)
at Microsoft.AspNetCore.Server.Kestrel.Transport.Sockets.SocketConnectionListener.Bind()
at Microsoft.AspNetCore.Server.Kestrel.Transport.Sockets.SocketTransportFactory.BindAsync(EndPoint endpoint, CancellationToken cancellationToken)
at Microsoft.AspNetCore.Server.Kestrel.Core.KestrelServer.<>c__DisplayClass21_0`1.<<StartAsync>g__OnBind|0>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.AddressBinder.BindEndpointAsync(ListenOptions endpoint, AddressBindContext context)
at Microsoft.AspNetCore.Server.Kestrel.Core.ListenOptions.BindAsync(AddressBindContext context)
at Microsoft.AspNetCore.Server.Kestrel.Core.AnyIPListenOptions.BindAsync(AddressBindContext context)
at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.AddressBinder.AddressesStrategy.BindAsync(AddressBindContext context)
at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.AddressBinder.BindAsync(IServerAddressesFeature addresses, KestrelServerOptions serverOptions, ILogger logger, Func`
2 createBinding)
at Microsoft.AspNetCore.Server.Kestrel.Core.KestrelServer.StartAsync[TContext](IHttpApplication`1 application, CancellationToken cancellationToken)
Unhandled exception. System.Net.Sockets.SocketException (13): Permission denied
at System.Net.Sockets.Socket.UpdateStatusAfterSocketErrorAndThrowException(SocketError error, String callerName)
at System.Net.Sockets.Socket.DoBind(EndPoint endPointSnapshot, SocketAddress socketAddress)
at System.Net.Sockets.Socket.Bind(EndPoint localEP)
at Microsoft.AspNetCore.Server.Kestrel.Transport.Sockets.SocketConnectionListener.Bind()
at Microsoft.AspNetCore.Server.Kestrel.Transport.Sockets.SocketTransportFactory.BindAsync(EndPoint endpoint, CancellationToken cancellationToken)
at Microsoft.AspNetCore.Server.Kestrel.Core.KestrelServer.<>c__DisplayClass21_0`1.<<StartAsync>g__OnBind|0>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.AddressBinder.BindEndpointAsync(ListenOptions endpoint, AddressBindContext context)
at Microsoft.AspNetCore.Server.Kestrel.Core.ListenOptions.BindAsync(AddressBindContext context)
at Microsoft.AspNetCore.Server.Kestrel.Core.AnyIPListenOptions.BindAsync(AddressBindContext context)
at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.AddressBinder.AddressesStrategy.BindAsync(AddressBindContext context)
at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.AddressBinder.BindAsync(IServerAddressesFeature addresses, KestrelServerOptions serverOptions, ILogger logger, Func`2 createBinding)
at Microsoft.AspNetCore.Server.Kestrel.Core.KestrelServer.StartAsync[TContext](IHttpApplication`1 application, CancellationToken cancellationToken)
at Microsoft.AspNetCore.Hosting.GenericWebHostService.StartAsync(CancellationToken cancellationToken)
at Microsoft.Extensions.Hosting.Internal.Host.StartAsync(CancellationToken cancellationToken)
at Microsoft.Extensions.Hosting.HostingAbstractionsHostExtensions.RunAsync(IHost host, CancellationToken token)
at Microsoft.Extensions.Hosting.HostingAbstractionsHostExtensions.RunAsync(IHost host, CancellationToken token)
at Microsoft.Extensions.Hosting.HostingAbstractionsHostExtensions.Run(IHost host)
at SanUserManagementService.Program.Main(String[] args) in /home/jankins/workspace/Daniel/dotnet/SanUserManagementService/Program.cs:line 10
Aborted (core dumped)
Any help related to this will be appreciated!
Thanks!

Answer 1

In my case the ASPNETCORE_URLS setting in environment variables or appsettings.json was set to http://+:80.
Changing it to http://+:5000 worked. Make sure you change your Docker port bindings as well, or load balancer settings if using AWS.

Answer 2

It works for me if the port is higher then 80. You need to run Kestrel on a different port within the code itself, maybe check the json files.

Answer 3

There might be running previous instance of your app in the server. Try running netstat -tulpn | grep LISTEN to see which PID is using the port(s) and kill it if necessary