Accessing .net core website hosted on Ubuntu 16.04 through internet

I am following along this tutorial to deploy my asp.net application onto Ubuntu. I have installed .Net core 2.0 on my Ubuntu machine using this post. NO issues with that excellent article.

My VM configuration is :

user@instance-2:~/dev/mywebsite$ lsb_release -a
    No LSB modules are available.
    Distributor ID: Ubuntu
    Description:    Ubuntu 16.04.3 LTS
    Release:        16.04
    Codename:       xenial

 user@instance-2:~/dev/mywebsite$ lsb_release -a
    No LSB modules are available.
    Distributor ID: Ubuntu
    Description:    Ubuntu 16.04.3 LTS
    Release:        16.04
    Codename:       xenial

user@instance-2:~/dev/mywebsite$ dotnet --info
.NET Command Line Tools (2.0.0)
Product Information:
 Version:            2.0.0
 Commit SHA-1 hash:  cdcd1928c9
Runtime Environment:
 OS Name:     ubuntu
 OS Version:  16.04
 OS Platform: Linux
 RID:         ubuntu.16.04-x64
 Base Path:   /usr/share/dotnet/sdk/2.0.0/
Microsoft .NET Core Shared Framework Host
  Version  : 2.0.0
  Build    : e8b8861ac7faf042c87a5c2f9f2d04c98b69f28d

Next I have created new dot net web application using below command

dotnet new web

set ASPNETCORE_URLS environment variable

export ASPNETCORE_URLS=http://+:5123

Confirmed that its set properly.

user@instance-2:~/dev/mywebsite$ echo $ASPNETCORE_URLS
http://+:5123

Ran my application using dotnet run. Can see below message on console.

user@instance-2:~/dev/mywebsite$ dotnet run
Hosting environment: Production
Content root path: /home/hemant_shelar/dev/mywebsite
Now listening on: http://[::]:5123
Application started. Press Ctrl+C to shut down.

Expected: I should be able to browse this site from internet using IP address like : http://35.185.21.120:5123/ But I am not able to access this site from outside. Getting ERR_CONNECTION_TIMED_OUT error.

Note: 35.185.21.120 is IP address of my Ubuntu machine which is in google cloud.

Am I missing any configuration?