This paper holds that Node.js The microservice architecture launched by us will completely subvert JavaEE Traditional application server concept ,Java The application server includes Tomcat JBoss Websphere Weblogic or Oracle Application server . The application server is Java EE or Servlet Containers .
We need an application server to deploy our application on each server , It's been a habit for years , But today we're going to ask , Why are we doing this ？ Why do we have to pay for the application server ？
The PPT From the four aspects of application server analysis ：
1. An application server is a container for multiple applications ？
2. The application server is the underlying infrastructure ？
3. Deployment of application server ？
4. Monitoring of application server ？
First , An application server is a container for multiple applications , The advantage of this is that you can pass through the application ClassLoader Isolation , They don't affect each other . Actually, it's just ClassLoader It's not enough to isolate the loading levels of classes ,CPU Memory Does the application system need to be isolated ？ otherwise , If a stand-alone application is very expensive CPU, Or will it affect other applications . In particular, we will JMS and Web On the same server ,JMS It will consume a lot of resources .
therefore , Isolation is impossible , Even if JVM Become an operating system , Isolation won't be perfect either .Linux Operating systems are isolated from each other by processes , however CPU Memory is also shared .
So what does it really mean to deploy multiple applications in one application server ？JavaEE The application of multiple applications refers to a component Component Concept , Not at all App, Such as WAR EJB JAR etc. . Different components are made up of different Classloader load , isolated .
The following figure shows JavaEE Three concepts of ：
application server --> App application ----> Multiple components
in other words , One application server corresponds to one App application , Not many App, It's multiple components , This is a JavaEE What application server really means . Multiple application servers can form a cluster .
secondly , The application server is the infrastructure , Provide some basic functionality , These functions include ： Two transaction commit (2PC) Networks and threads and infrastructure API.
2PC It's a cross database transaction mechanism , Ensure the atomicity of complex operations , adopt JMS Distributed transaction can be realized . however 2PC There are the following problems ： It reduces processing performance , No 100% reliable ,2PC It will also fail , There are limitations in distributed environments , For new technologies that cannot be used , Such as REST + 2PC? NoSQL + 2PC? The biggest problem is NoSQL Critically , There's no expansibility scalability.
Network and thread facilities include database connection pool and Http Thread pool and so on ,JavaEE Of API Include EJB, CDI, JPA, JSF etc. , The real problem is ： The version is tightly coupled with the application server version , So it can be applied App Heavily dependent on application servers , Until a new application server is released , Otherwise the new API Can't use ,API Version conflicts are on the rise .
These infrastructures can't cover the common application through , Additional library packages need to be added , Finally, the application server is replaced by the library package , The application can carry the library package for transplantation , It's more transplantable . therefore , The application server is the same as the library package , It should be just another part of the application , otherwise ...
Advocate application server independence , This results in each application server having its own infrastructure , For example, database connection pool Special configuration method , Even added their own additional library package to the application server , Finally, it leads to a dependency loop , application app And the application server depend on different versions of the same package , It's hard to coordinate .
Application server independence also leads to differences between servers , Even different versions of servers are different , As a result, our applications can not be deployed seamlessly to the servers of these different manufacturers .
in addition , Application servers are not a common infrastructure , The batch MapReduce Etc. does not provide , It's just one kind of infrastructure .
Last , Application server can provide the function of deploying application and monitoring running , But it's always about complex tools , For example, the deployment format has WAR, EAR, JAR Three , Deployment tools use Maven Etc script , Monitoring is based on JMX and SMNP There are a lot of tool families . In today's increasingly frequent deployment , Simple deployment is more important , At this time, the application server becomes a headache .
therefore , These characteristics of application server lead to all kinds of problems today , Do we have to continue to struggle like this ？
Today's demand for products is Continuous Delivery Under the pressure of continuous delivery , We need a simpler infrastructure , A simpler way to deploy .
Nowadays, microservice architecture is becoming more and more popular , It has the following characteristics ：
• Be able to build software based on service composition
• Service means business Like an order Order, Catalog Directory and other services
• Services can be redeployed independently
• Compared with traditional applications, they are deployed to the application server as a whole , Microservices can be deployed independently .
• Between microservices REST Communications .
So our problem is ： Do you want to install an application server for each microservice ？ Very heavy .
The proposal of microservice architecture undoubtedly subverts the traditional concept of application server , Now we can abandon the application server , Do it ：
Create a JAR file , It contains a main Class is used to start , There are optimized and customized Infrastructure Library packages, such as Http The server etc. .
Easy to deploy in terms of deployment , Because there's only one JAR package , Then there are some command line configurations , These are standard deployment tools , Monitoring tools are also standard , For example, based on REST URL Monitoring of , Log files, etc .
banq notes ： Application servers are usually Java Another name for middleware , The application server is dead , The middleware concept becomes lightweight , Responsible for scalability Scalable Some of the middleware in Cloud Computing Paas replace . Reference resources ： Cloud computing Paas Five floors