I tried to open TensorBoard page from running
tensorboard --logdir=./Train_log/tb_train_log --port=8080 on Google Cloud Compute Engine VM instance. And the output web page http:<usename>:8080 is not available. The error when I opened the page is : 
Error: Could not connect to Cloud Shell on port 8080.
Ensure your server is listening on port 8080 and try again.
So I looked up to Unable to open Tensorboard in browser and Can't open port 8080 on Google Compute Engine running Debian.
Then I
1) set up the fire wall with creating a new rule as tcp:8080 and IP ranges 0.0.0.0/0.  
2) changed the port to 8080 and the default output 6006, changed the host to 0.0.0.0 and 127.0.0.1. Copy and paste corresponding address like http:0.0.0.0:8080 to google chrome. 
3) use web preview through google cloud shell to the port I set as above. 
Also the output of netstat -an | grep "LISTEN " is 
tcp        0      0 0.0.0.0:8080            0.0.0.0:*               LISTEN     
tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN     
tcp        0      0 127.0.0.1:631           0.0.0.0:*               LISTEN     
tcp6       0      0 :::22                   :::*                    LISTEN     
tcp6       0      0 ::1:631                 :::*                    LISTEN 
None of those worked, I wonder how to fix the problem ?
Any idea would be helpful !