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This article is about a sample analysis of scalable mail services in a Linux server cluster system. The editor thinks it is very practical, so share it with you as a reference and follow the editor to have a look.

Linux cluster system is a solution adopted by many contemporary companies. Linux cluster is connected by multiple machines to deal with complex problems. Homogeneous or heterogeneous computers can be connected together to complete specific tasks. This forms a cluster. LVS is the abbreviation of Linux virtual server, which means Linux virtual machine service.

With the growing number of Internet users, many ISP face the problem of overloading their mail servers. When the mail server cannot accommodate more user accounts, some ISP will buy a more high-end server to replace the original one. It is a tedious task to migrate the information from the original server (such as user mail) to the new server, which will cause service interruption. Some ISP sets up new servers and new mail domain names, and new mail users are placed on new servers. For example, Shanghai Telecom now uses different mail servers public1.sta.net.cn, public2.sta.net.cn to public9.sta.net.cn to place users' mail accounts. This static division of users to different servers will result in unbalanced mail server load and low resource utilization of the system. It is difficult for users to remember the e-mail address.

Figure 5: scalable mail cluster based on LVS

The LVS framework can be used to implement a highly scalable and highly available mail service system. Its architecture is shown in figure 5: at the front end is a load scheduler using IP load balancing technology; the second layer is a server pool with LDAP (Light-weight Directory Access Protocol) servers and a set of mail servers. The third layer is data storage, which stores users' mail through a distributed file system. The nodes in the cluster are connected through a high-speed network.

User information, such as user name, password, home directory and mail capacity limit, is stored in the LDAP server and can be managed by the administrator through HTTPS. Run SMTP (Simple Mail Transfer Protocol), POP3 (Post Office Protocol version 3), IMAP4 (Internet Message Access Protocol version 4), and HTTP/HTTPS services on each mail server. SMTP accepts and forwards the user's mail, and the SMTP service process queries the LDAP server to get the user information, and then stores the mail. POP3 and IMAP4 get the user information through the LDAP server, and after password verification, the user's mail access request is processed. Here, there needs to be a mechanism to avoid conflicts between reading and writing user mail by SMTP, POP3, and IMAP4 service processes on different servers. The HTTP/HTTPS service allows users to access mail through a browser.

The IPVS scheduler distributes the load of SMTP, POP3, IMAP4 and HTTP/HTTPS request flows to each mail server more evenly. Judging from the processing flow of the above services, no matter which mail server the request is sent for processing, the result is the same. Here, running SMTP, POP3, IMAP4 and HTTP/HTTPS on each mail server for centralized scheduling is helpful to improve the resource utilization of the whole system.

The possible bottleneck in the system is the LDAP server, which can achieve higher performance by optimizing the parameters of the B+ tree in the LDAP service and combining with the high-end server. If the distributed file system does not have a load balancing mechanism among multiple storage nodes, a corresponding mail migration mechanism is needed to avoid the tilt of mail access.

In this way, the cluster system is like a high-performance, highly reliable mail server for users (for example, Shanghai Telecom only needs to use a mail domain name public.sta.net.cn). When the number of mail users is growing, just add server nodes and storage nodes to the cluster. The centralized storage of user information makes user management easy, and the cluster system helps to improve the utilization of resources.

Thank you for reading! This is the end of this article on "sample analysis of scalable mail services in Linux server cluster system". I hope the above content can be of some help to you, so that you can learn more knowledge. if you think the article is good, you can share it for more people to see!

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