Hello Liuhongbo,
This could be related to the the Service Interruption in the in the Network Infrastructure : North Central US. "From approximately 22 July, 2015 01:58 to 03:08 UTC a subset of customers using Network Infrastructure in North Central US, Australia East,
East US and West US may have experienced DNS resolution failures to our services. Engineering teams have identified the root cause and deployed a mitigation. We have confirmed that normal service availability has been restored to all regions. This issue is
now mitigated"
http://azure.microsoft.com/en-us/status/#history
However, we are unable to confirm untill we look into the backend logs. If you are still facing the issue with your websites, I request you to create a Suppport Ticket. You can follow the link below and choose technical to create a support
ticket:
http://azure.microsoft.com/en-us/status/#history
Thanks,
Syed Irfan Hussain