这个对话链接应该用TCP/IP来做吧？好像还设计到数据存储，需要再做个数据库吗？
Infrastructure - Chatting:
Imagine you are tasked with designing a chatting service that allows for 1
to 1 chats.
Assume that there is no requirement to store conversation history.
Provide a high level description of the system components you would use to
create the chat service.
Describe how your infrastructure would scale up to millions of users per day.
How would you modify your system to support offline messaging when the
recipient is not currently connected?
