To "system architecture of large, high-concurrency and high-load websites"

Source: Internet
Author: User

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I have set up a dial-up access platform in CERNET, developed it on the front-end platform of the load search engine in yahoo3721, and upgraded the architecture of large-scale community sows, at the same time, I have worked with and developed many large and medium-sized website modules. Therefore, I have accumulated some experience in large websites to cope with high-load and concurrent solutions. I can discuss this with you.

A small website, such as a personal website, can be implemented using the simplest HTML static page. With some images for beautification, all the pages are stored in a directory, such websites have very simple requirements on system architecture and performance. With the increasing diversity of Internet services, website-related technologies have been subdivided into many aspects after years of development, especially for large websites, the technology is widely used. From hardware to software, programming language, database, Webserver, firewall and other fields, there are high requirements, it is no longer comparable to a simple HTML static website.

Large websites, such as portal websites. In the face of a large number of user access and high concurrency requests, the basic solution focuses on the following aspects: use high-performance servers, high-performance databases, high-efficiency programming languages, and high-performance WEB containers. However, in addition to these aspects, it is impossible to fundamentally solve the high load and high concurrency problems faced by large websites.

The solutions provided above also mean a greater investment to a certain extent, and these solutions have bottlenecks and do not have good scalability, I will talk about some of my experiences from the perspectives of low cost, high performance, and high scalability.

1. HTML static
As we all know, the most efficient and least consumed HTML pages are purely static html pages, so we try our best to make the pages on our website adopt static pages, this simplest method is actually the most effective method. However, for websites with a large amount of content and frequent updates, we cannot manually implement them all, so we have a common information publishing system CMS, news channels such as the portals we often visit, and even other channels, are managed and implemented through the information publishing system, the information publishing system can automatically generate static pages based on the simplest information input. It can also provide channel management, permission management, automatic crawling, and other functions. For a large website, having an efficient and manageable CMS is essential.

In addition to portal and information publishing websites, static websites with high interaction requirements are also a necessary means to improve performance, static Community posts and articles in real time, and re-static updates are also a lot of use strategies, such as mop, the same is true for the Netease community.

At the same time, HTML static is also a method used by some caching policies. For applications that frequently use database queries but have little content updates in the system, you can consider using HTML static, for example, the public setting information of the Forum in the forum. Currently, mainstream forums can perform background management and store the information in the database. In fact, this information is frequently called by foreground programs, but the update frequency is very small, you can consider static content during background updates to avoid a large number of database access requests.

2. image server Separation
As we all know, for Web servers, images, whether Apache, IIS or other containers, consume the most resources. Therefore, it is necessary to separate images from pages, this is basically a strategy adopted by large websites. They all have independent image servers and even many image servers. This architecture can reduce the pressure on the server that provides page access requests, and ensure that the system does not crash due to image problems. Different configurations can be optimized on the application server and image server, for example, Apache can provide as few support as possible when configuring contenttype.
Loadmodule ensures higher system consumption and execution efficiency.

3. Database Cluster and database table hash
Large websites have complex applications, and these applications must use databases. In the face of a large number of accesses, database bottlenecks will soon become apparent. At this time, a database will soon fail to satisfy applications, therefore, we need to use a database cluster or database table hash.

In terms of database clusters, many databases have their own solutions, and Oracle and Sybase all have good solutions. The commonly used MySQL Master/Slave is also a similar solution, you can refer to the corresponding solutions to implement the database.

As the database cluster mentioned above is limited by the DB type used in terms of architecture, cost, and expansion, we need to consider improving the system architecture from the perspective of applications, database table hashing is a common and most effective solution. We install business and application or function modules in the application to separate the database. Different modules correspond to different databases or tables, then, according to a certain policy, conduct a smaller database hash for a page or function, such as a user table and table hash by user ID, in this way, the system performance can be improved at a low cost and the scalability can be improved. Sohu's Forum adopts this architecture to separate the database of Forum users, settings, posts, and other information, and then hash the databases and tables of posts and users according to sections and IDs, the simple configuration in the configuration file allows the system to add a low-cost database at any time to supplement the system performance.

4. Cache
The word cache has been used in many areas. The cache in website architecture and website development is also very important. Here we will first describe the two most basic caches. Advanced and distributed caching are described later.
For architecture caching, anyone familiar with Apache can know that Apache provides its own cache module, or use the plus squid module for caching, both methods can effectively improve Apache's access response capabilities.
The memorycache provided on Linux is a common cache interface that can be used in Web development. For example, it can be called during Java development.
Memorycache caches and shares data, and some large communities use this architecture. In addition, when using Web language development, various languages basically have their own cache modules and Methods. php has a pear cache module, and Java has more ,. net is not very familiar with, I believe there must be.

5. Images
Images are often used by large websites to improve performance and data security. The image technology can solve the differences in user access speed caused by different network access providers and regions, such as Chinanet and
The difference between EduNet has prompted many websites to set up mirror sites in CERNET, and regularly update or update data in real time. In terms of image details, I will not elaborate too deeply here. There are many professional off-the-shelf solutions and product options. There are also low-cost software implementation ideas, such as rsync on Linux and other tools.

6. Server Load balancer
Server Load balancer is the ultimate solution for large websites to solve high-load access and a large number of concurrent requests.
Server Load balancer has been developing for many years. There are many professional service providers and products to choose from. I personally have some solutions, including two architectures for your reference.
Hardware layer-4 Switching
The layer-4 Exchange uses the header information of the layer-3 and layer-4 information packets to identify business flows based on the Application interval and distribute the business flows of the entire interval segment to appropriate application servers for processing. The layer-4 switching function is like a virtual IP address pointing to a physical server. Its transmission services are subject to a variety of protocols, including HTTP, FTP, NFS, telnet, or other protocols. These services require complex load balancing algorithms based on physical servers. In the IP address world, the service type is determined by the TCP or UDP port address of the terminal. The application interval in the layer-4 switch is jointly determined by the source and terminal IP addresses, TCP and UDP ports.
In the field of hardware layer-4 switching products, there are some well-known products to choose from, such as Alteon and F5. These products are expensive, but value for money, it provides excellent performance and flexible management capabilities. Yahoo China used three or four Alteon servers on nearly 2000 servers.

Layer-4 software exchange
After learning about the principle of the hardware layer-4 switch, the four-layer switch based on the OSI model came into being. Such a solution achieves the same principle, but has a poor performance. However, it is easy to meet a certain amount of pressure. Some people say that the software implementation method is actually more flexible, and the processing capability depends entirely on the familiarity of your configuration.
For layer-4 software exchange, we can use LVS, which is commonly used in Linux. LVS is a Linux
Virtualserver, which provides a real-time disaster response solution based on heartbeat, improves system robustness and provides flexible virtual VIP configuration and management functions, it can meet multiple application requirements at the same time, which is essential for distributed systems.

A typical load balancing strategy is to build a squid Cluster Based on layer-4 software or hardware exchanges. This idea is adopted on many large websites, including search engines, this architecture is low-cost, high-performance, and highly scalable. It is easy to increase or decrease nodes in the architecture at any time. I have prepared a special detail for this architecture and will discuss it with you.

For large websites, each method mentioned above may be used at the same time. I will introduce it more easily here. You need to be familiar with and understand many details during the implementation process, sometimes a very small squid parameter or Apache parameter setting will have a great impact on the system performance. I hope you can discuss it together to make it effective.

A very good article, basically all things that need to be done on a large website have been mentioned. I have also worked in one of the three major portals and managed more
Squid of 100 machines
I hope I can share my experiences and opinions.

1. image server Separation
I have always supported this idea. Especially if the program and the image are both placed in the same
Under the apahce server, every image request may lead to an httpd process call. If httpd contains a PHP module, it will occupy too much memory, this is not necessary.

Using an independent image server not only avoids the above situation, but also sets different expiration times for images of different usage properties, so that the same user will not retrieve data from the server (based on the Cache Server) again when accessing the same image on different pages, not only fast, but also saves bandwidth. In addition, you can adjust the cache time.

In the image server I managed in the past, not only does it separate images from applications and pages, but it also enables different domain names for different types of images. To ease the pressure on images of different types. For example
The domain name is used for photography services. It usually uses five caches, but after 5.1 long holidays, it may need to increase the number of independent hosts to 10.
. These 5 servers can be temporarily transferred from other low-load image servers.

2. Database Cluster
A cluster of Oracle RAC is arranged in
About 40 W, this price is unnecessary for general companies. Because the web application logic is relatively simple, and the value of Oracle large databases lies in data mining, rather than simple storage. Select MySql or
PostgreSQL will be more practical.

Simple MySQL replication can achieve better results. Read from slave and write to master
. In actual situations, MySQL's replication performance is very good, basically it will not bring too high update latency. Using the balance ( software, listen to 3306 locally (
Port, and then map multiple slave databases to achieve load balancing.

3. Are images stored on disks or databases?
I have carefully considered this issue. If
In the ext3 file system, the limit is reached when directories are created, but XFS is not used. To store images in large quantities, you must separate them into many small directories. Otherwise
Ext3 can only be set to 3 W
Directory restrictions, and too many files and directories will affect disk performance. There are no problems such as space waste.

More importantly, data backup for a large number of small files takes a lot of resources and a very long time. Before these problems, it may be another option to save images in the database.

You can try to save the image to the database.
The PHP program returns the actual image and places a squid server on the front end to avoid performance problems. You can also use MySQL to back up images.
Data replication mechanism. This problem can be effectively solved.

4. I won't talk about static pages. I made my own WordPress.
Static data is fully realized, while dynamic data generation can be well taken into account.

5. Cache
I have also proposed to use
Memcached, but it is not very ideal in actual use. Of course, inconsistent use results may occur in different application environments, which is not important. As long as you think it is easy to use.

6. layer-4 software exchange
The performance is very good. My friend's website uses LVS as the Scheduler for balancing, and the data volume is very large and can be easily supported. Of course, Dr is used.

In fact, I also thought I could use it.
LVS is used for CDN scheduling. For example
The BGP data center accepts users' requests and then dispatches the requests to the actual physical servers of the Telecom or Netcom data center in the Tun mode of LVS, directly returning data to the user.

This is Wan.
F5 hardware devices also use this technology. However, the cost of using LVS is greatly reduced.

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