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July 11, 2022

Config Service

Overview

1. Service without config service
2. Service with config service
3. Pros and Cons
4. References

Service without config service

The configuration files (e.g. application.yaml, application.properties, bootstrap.yaml) will be maintained in the resources directory of your service application.

my-app
|_ src
    |_ main
        |_ java
        |_ resources
            |_ application.yaml
            |_ application-local.yaml
            |_ application-dev.yaml
            |_ application-uat.yaml
            |_ application-prod.yaml
|_ test
|_ pom.xml

application.yaml:

spring:
    application:
        name: my-app

server:
    port: 8080

application-dev.yaml:

server:
    port: 8081

application-uat.yaml:

server:
    port: 8082

application-prod.yaml:

server:
    port: 8083

Running the application with profiles:

$ mvn spring-boot:run -Dpring.profiles.active=dev

Service with config service

Using a config service, we will place our configuration properties in environment specific directories (e.g. dev, uat, prod, local). Notice that the file name is now renamed to the actual application name (i.e. dev/my-app.yaml instead of previously resource/application-dev.yaml):

config-service
|_ src
    |_ main
        |_ java
            |_ demo
                |_ ConfigServerApplication.yaml
        |_ resources
            |_ application.yaml
            |_ dev
                |_ my-app.yaml
            |_ uat
                |_ my-app.yaml
            |_ prod
                |_ my-app.yaml
            |_ local
                |_ my-app.yaml
|_ test
|_ pom.xml

application.yaml

spring:
    application:
        name: configserver

server:
    port: 8888

Add the @EnableConfigServer annotation in your main application class:

package demo;

import org.springframework.cloud.config.server.EnableConfigServer;

@EnableConfigServer
public class ConfigServerApplication {

    public static void main(String args[]) {
        SpringApplication.run(ConfigServerApplication.class, args);
    }
}

Run the config service app:

$ mvn spring-boot:run

You can then retrieve the configuration by app and profile using the config service endpoint:

http://localhost:8888/{app}/{profile}

Example:

http://localhost:8888/my-app/local
http://localhost:8888/my-app/dev
http://localhost:8888/my-app/uat
http://localhost:8888/my-app/prod

Then in our my-app application, we simply specify the spring cloud config uri in resources/application.yaml:

my-app
|_ src
    |_ main
        |_ java
        |_ resources
            |_ application.yaml
|_ test
|_ pom.xml

spring:
    cloud:
        config:
            uri: ${CONFIG_SERVER_URI:${vcap.services.${PREFIX:}configserver.credentials.uri:http://user:password@localhost:8888}}

Running the application is the same, we simply specify the active profiles to use:

$ mvn spring-boot:run -Dpring.profiles.active=dev

Pros and Cons

Pros of using a config service:

1. Configuration properties are maintained in a common repository
2. No need to build and deploy service application due to config change. Make changes in config service repository and redeploy config service
3. Build, deploy and app start up time of a config service is usually much faster than a service application

References

https://spring.io/projects/spring-cloud-config#overview