Redundant web and mail system 　→ 日本語

Both web server and mail server have identical copies for redundancy

• User can simply use the servers with one address

server	host name
Web	www.rcnp.osaka-u.ac.jp
Imap4	imap4.rcnp.osaka-u.ac.jp
SMTP	smtp.rcnp.osaka-u.ac.jp

• However in practice changing the default server automatically in a case of failure is difficult.
• In the case of trouble the web/imap server used will be switched by administrator (SE).
• When trouble occurs, users have to wait for this change to happen.
• smtp servers allow bit more complicated setup which elevates availability.
• If one of the smtp servers which you use fails, you will get error when sending a message. Mail clients usually can change the sending server, and if you change the sending server, sending mail will work. Email clients can't confirm if SMTP server is working or not, so they switch to other server for a while and then try the previous one again. After a while this will happen again. This is better than not being able to send mail at all.

In the case of failure, system administrator (SE) will disable the malfunctioning server, and only the working server will be used.

• It's not visible to the users, but the mails are kept in two places, even if a hard disk breaks on the mail server the other copy will still remain. The two copies are made in real time, so even in unexpected power failure occurs, data loss rarely happens.
• The two servers are separated physically, (Ring Cyclotron building and IT building) so even if one of them loses power the other one will still be able to provide services normally.
• For experienced users, a method to change between the 2 servers is explained below.
  • Without relaying on DNS, this method directly sets the IP addresses for the servers by modifying hosts file.
  • If you don't understand the changes you are making to your hosts file you can cause problems for your computer. Only use this method after understanding what you are doing. The Computer and Network Group is not responsible for problems caused by following these instructors.
  • On unix systems the hosts file is located in /etc/hosts, and on Windows in C:\Windows\System32\drivers\etc\hosts
  • For what to add to the hosts file refer to here. Remove "#"s for the pattern you want to use.
  • In the file there are 4 different patterns for different situations, only use one of the patters at a time.
  • indico is only running on server 1, even if you switch using this method, it won't work.