客户端唯一性判断

[zhaohfup]

一个tomcat下部署多个war包，每个war包都有一个app.id，但实际只有第一个启动的war包链接上了apollo，其他war包使用的配置全部来源于第一个启动的war服务。问题是这种机制原理是什么？

[nobodyiam]

You may take a look at DefaultApplicationProvider.

[zhaohfup]

像我们这种情况多个app.id同时生效怎么配置？

[Anilople]

see https://www.apolloconfig.com/#/zh/usage/java-sdk-user-guide

source code

https://github.com/apolloconfig/apollo/blob/master/apollo-core/src/main/java/com/ctrip/framework/foundation/internals/provider/DefaultApplicationProvider.java#L119-L148

Maybe you can write app.id to your own META-INF/app.properties.

[iambiglee]

你用的应该是第三种方法，第三种不支持war包的形式，可以采用第四种方式

[iambiglee]

多个war包只有一个appid生效的原理如下：
ApolloApplicationContextInitializer，实现了EnvironmentPostProcessor接口，该接口中有个初始化方法。通过改初始化方法，最终调用方法fillSystemPropertyFromEnvironment，会将配置文件中的["app.id", "apollo.cluster", "apollo.cacheDir", "apollo.meta"]放到System中去，一个JVM线程只有一个System.这就导致了一个tomcat启动后，app.id 会被一直覆盖，所以只有一个app id 生效。

[iambiglee]

By the way a question.
Why use System to store app.id and staff ?
In the case of multiple war packages in a tomcat, This will cause app.id to overwrite each other.
Would it be better if use custom local ConCurrentHashMap to store it?
Or there are some specific situation that I didn’t think about.
Tks.

[nobodyiam]

Apollo uses System Property to store app.id to ease the configuration, e.g. user could pass the app.id as -Dapp.id=xxx.
The use of ApolloApplicationContextInitializer is to ease the configuration for spring boot, e.g. user could set the app.id in the application.properties.
However, if users set the app.id in META-INF/app.properties, it won't be stored to System Property, which I think would work in your scenario.

[iambiglee]

Got it, Tks