central-dogma-demo

startup

There are CentralDogma Docker images in Docker Hub, so pull and run.

docker run -p 36462:36462 line/centraldogma:0.52.1

Open http://127.0.0.1:36462 in your browser to access administrative console.

settings for this repository

MEMO: We can use command-line client for some settings, but it's easy to use administrative console.

1. Create project 'demo'.
2. Create repository 'lottery' in 'demo' project.
3. Create json file 'chance.json' in 'lottery' repository as below.

{
  "chance": 50
}

See chance_sample.json .

run application

Run Application to use following command at project root.

./gradlew bootRun

You can draw a lot to access http://127.0.0.1:8080/draw.

Winning chance of the lot is the one defied at CentralDogma, i.e., if you use 'chance.json' above as it is, the winning chance is 50%.

The winning chance appears in log like this.

c.c.demo.service.LotteryService          : The chance of winning is 50%

change settings

CentralDogma enables us to use new settings without restarting application.

Change chance value in 'chance.json'.

{
  "chance": 90
}

Draw a lot to access http://127.0.0.1:8080/draw, and you'll see in log that the winning chance changed.

c.c.demo.service.LotteryService          : The chance of winning is 90%

how to use CentralDogma

Assume you are using Spring Framework.

add dependency

Add com.linecorp.centraldogma:centraldogma-client-spring-boot-starter:0.52.1 to build.gradle.kts.

dependencies {
    implementation("com.linecorp.centraldogma:centraldogma-client-spring-boot-starter:0.52.1")
}

add configuration

Add a new section called centraldogma which contains some settings, e.g., hosts.

centraldogma:
  hosts:
    - 127.0.0.1:36462

create watcher

When you finish adding dependency and configuration, you can use com.linecorp.centraldogma.client.CentralDogma . So, inject the client.CentralDogma into your application.

Create com.linecorp.centraldogma.client.Watcher to use a method of client.CentralDogma which is injected.

One of the method to create the client.Wathcer is fileWatcher.

name	type	description
projectName	String	project name of CentralDogma
repositoryName	String	repository name of CentralDogma
query	com.linecorp.centraldogma.common.Query<T>	query on the file
function	java.util.function.Function<? super T, ? extends U>	function which converts from (? super T) to (? extends U)

If you put json file in CentralDogma, you use Query.ofJson(jsonPath) as a third argument, so a fourth argument is Function<? Super JsonNode, ? extends T>.

awaitInitialValue

You can specify a timeout and a default value by using watcher.awaitInitialVallue(). If not using this method, your application has possibility of awaiting indefinitely.

According to an official document , recommended timeout value is 20 seconds or more.

It is generally recommended to use a value not less than 20 seconds so that the client can retry at least a few times before timing out.

get latest value

Get the latest value by using watcher.latestValue().

reference

https://line.github.io/centraldogma/