Hi @sam I manually install discourse, how could I update the SMTP setting besides through the config/environment/development.rb. Does the discourse.config fit the need?
You should be putting the mail settings in the env block of the app.yml which is parsed by the launcher script.
Is there any reason not to use Docker on this machine?
Yes, setting these options in /config/discourse.conf would work, e.g.
smtp_address = 10.0.0.1
smtp_port = 25
# etc...
However, this really isn’ the supported way to install Discourse. 
(All of these settings can also be given as environment variables to Unicorn; simply capitalize the setting’s name and add a DISCOURSE_ prefix.)
I am using docker which is nice tool for deployment. However in my case, I gonna quickly test some configurations variables within the docker without rebuild the container every time.
why isn’t updating the /config/discourse the supported approach? 
Hm, with “not supported” I’m not saying that it won’t work, but that you may get ignored if you run into problems during the installation and ask for help. After all, anyone trying to help would be guessing at what you’ve changed and basically poking in the dark to determine what’s wrong. 
This seems to have stopped working, even though I’m changing /var/www/discourse/config/discourse.conf — it seems to be reset at container startup O_O.
I can’t be sure though — some processes are hanging in kernel-space, in aufs-related code, so changes might be just getting lost because of aufs, instead of being reset by userspace. I’ll try again later.