With the increasing number of high-level concurrent access and massive data processing scenarios on large websites, it is increasingly important to achieve high-availability, scalability, scalability, and security goals. In order to solve such a series of problems, the architecture of large websites is also constantly evolving. To improve the high-availability architecture of large websites, it is necessary to mention distributed. This paper briefly introduces the concept of distributed systems, the characteristics of distributed systems, commonly used distributed solutions, and the differences between distributed and clustered.
This is an article I posted before in my blog. I am about to expand some articles about distributed issues. I will post some basic articles in the public number and look at friends I have never seen before.
First, the centralized system before learning to distribute, first understand what the corresponding centralized system looks like.The centralized system is summarized in one sentence: one host with multiple terminals. The terminal has no data processing capability and is only responsible for data entry and output. The calculation, storage, and the like are all performed on the host.
Take an example of an electronic mall, an electronic mall of a centralized system, implemented by an application, deployed on a host to provide external services. All user operations are implemented by an application on this machine.
The biggest feature of the centralized system is that the deployment structure is very simple. The bottom layer generally uses expensive mainframes purchased from IBM, HP and other vendors. Therefore, there is no need to consider how to deploy multi-node services, and thus do not consider the distributed collaboration between nodes.
However, due to the stand-alone deployment. It is very likely that the system is large and complicated, difficult to maintain, and a single point of failure (when a single point fails, it will affect the entire system or network, resulting in flaws in the entire system or network), poor scalability, and the like.
Distributed system backgroundIt is said that a distributed system must be a centralized system. The entire project in a centralized system is an independent application. The entire application is the entire project, and everything is in one application.
As shown below
For example, a website is an application, and finally a plurality of servers or multiple containers are added to achieve load balancing to avoid single point of failure. Of course, the database can be deployed separately.
The obvious advantage of centralized is that it is convenient to develop test and operation and maintenance, and it is not necessary to consider complex distributed environments.
The obvious drawback of centralized is that it is not easy to extend, and all applications must be updated for each update. Moreover, a problem means that all applications have problems. When the system is getting bigger and bigger, centralized will be the biggest bottleneck of the system.
What is a distributed system?A distributed system is a collection of separate computers that are like a single related system to a user.
That is to say, behind a distributed system is a series of computers, but the user does not perceive the logic behind it, just like accessing a single computer.
Speaking a bit, we can simply look at the distributed system diagram.
In a distributed system:
1. The application can be divided into multiple applications according to the service type, and then divided into interface layer and service layer according to the structure; we can also define different interface applications according to the access point, such as mobile terminal and PC end;
2. The database can be split into multiple instances according to the business type, and the sub-library tables can be divided into single tables;
3. Add middleware such as distributed cache, search, file, message queue, and non-relational database;
Obviously, the distributed system can solve the drawbacks of centralized inconvenience expansion. We can easily extend the application in any part, even if there is a problem in one application, it will not affect other applications.
With the popularity of the micro-service Spring Cloud & Docker and the rebirth of the domestic open source distributed Dubbo framework, distributed technology is developing very rapidly.
Although the distributed system is good, it also brings the complexity of the system, such as distributed transactions, distributed locks, distributed sessions, data consistency, etc., which are all problems that need to be solved in distributed systems, although there are already many mature ones. The plan, but not perfect. Distributed systems also increase the cost of development test and operation, increase the workload, and poor management of distributed systems can become a burden.
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