spring boot uses k8s configMap as external configuration

1. Overview

spring boot application to run on the k8s cluster as a container, but different environments require different configuration files. We can use an external configuration center, such as nacos , apollo . k8s also provides configMap to decouple the environment configuration information from the container image to facilitate the modification of the application configuration. This article mainly introduces the use of spring boot k8s of configMap as the external configuration from the following aspects:

• spring boot Load configuration file introduction
• k8s of configMap
• Use k8s of configMap as the external configuration file

2. Introduction to spring boot loading configuration file

When the application starts, Spring Boot will automatically find and load the application.properties and application.yaml files from the following locations.

The order of configuration file priority from highest to lowest is as follows:

1. file:./config/ -the highest priority ( /config subdirectory under the project root path)
2. file:./ -second priority (under the project root path)
3. classpath:/config/ -the third priority (under item resources/config )
4. classpath:/ -the fourth priority (project resources root directory)

High priority configuration will override low priority configuration

application.properties and application.yaml files in the same directory, then application.properties will overwrite the application.yaml file

If we want to specify the configuration file of which environment to run when we run, there are three ways:

1. Configure spring.profiles.active=dev specify the loading environment application.properties file under the project resources folder
2. When starting the jar, specify the environment loaded by --spring.profiles.active=prod
3. When starting the jar, specify --spring.config.location=target/application.properties load the configuration file location

3. Introduction of 060e8101e28f18 of configMap

ConfigMap is a API object used to store non-confidential data in key-value pairs. When used, pod can be used as environment variables, command line parameters or configuration files in storage volumes.

Note :

ConfigMap does not provide confidentiality or encryption functions. If the data you want to store is confidential, please use secret or use other third-party tools to ensure the privacy of your data instead of ConfigMap .

ConfigMap is not designed to save large amounts of data. The data stored ConfigMap 1 MiB . If you need to save data that exceeds this limit, you can consider mounting a storage volume or using a separate database or file service.

Several ways to create configMap

1. uses the directory to create ( --from-file specifies that all files in the directory will be used to ConfigMap . There are as many key-value pairs as there are files. key is the file name, and the value is the file name. Content )

   kubectl create cm [configmap名称] --from-file=[目录]

2. use file to create ( --from-file this parameter can be used multiple times, the effect is the same as specifying the entire directory)

   kubectl create cm [configmap名称] --from-file=[文件] --from-file=[文件]

3. created from a literal ( --from-literal this parameter can be used multiple times)

   kubectl create cm [configmap名称] --from-literal=[键=值] --from-literal=[键=值]

Example: Use literal values to create a configMap

 kubectl create cm myconfigMap --from-literal=env=dev --from-literal=name=test

[root@node01 test]# kubectl describe cm myconfigMap
Name:         myconfigmap
Namespace:    default
Labels:       <none>
Annotations:  <none>

Data
====
env:
----
dev
name:
----
test
Events:  <none>

4. use yaml manifest file to create

   Create a game-demo.yaml file with the following content:

   apiVersion: v1
   kind: ConfigMap
   metadata:
     name: game-demo
   data:
     # 类属性键；每一个键都映射到一个简单的值
     player_initial_lives: "3"
     ui_properties_file_name: "user-interface.properties"
   
     # 类文件键，键的名字就是文件名，值就是文件的内容
     game.properties: |
       enemy.types=aliens,monsters
       player.maximum-lives=5    
     user-interface.properties: |
       color.good=purple
       color.bad=yellow
       allow.textmode=true    

Use the following command to create configMap :

kubectl apply -f game-demo.yaml

4. ☀️ Use k8s's configMap as an external configuration file

From the previous description we can know, spring boot loader highest priority profile is under the project root path /config subdirectory , so it can be configMap mount configuration files to the project root container config child Directory.

1. You can use the following command to create a configMap from the file:

kubectl create cm  spring-boot-demo  --from-file=application.yaml

2. Create a spring-boot-demo.yaml file with the following content:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: spring-boot-demo
  namespace: default
  labels:
    app: spring-boot-demo
spec:
  replicas: 1
  selector:
    matchLabels:
      app: spring-boot-demo
  template:
    metadata:
      labels:
        app: spring-boot-demo
    spec:
      containers:
        - name: spring-boot-demo
          image: ${ORIGIN_REPO}/spring-boot-demo:${IMAGE_TAG}
          imagePullPolicy: Always
          env:
            - name: TZ
              value: Asia/Shanghai
          ports:
            - containerPort: 8080
          resources:
            requests:
              cpu: 200m
              memory: 500Mi
          # 指定配置文件挂载到 /app/config 目录下，构建镜像时的jar包也在 /app 目录下
          volumeMounts:
            - mountPath: /app/config
              name: config
      imagePullSecrets:
        - name: docker-password
      volumes:
        - configMap:
            # 指定我们创建的configMap的名字
            name: spring-boot-demo
          # 自定义的名字，需要跟 volumeMounts.name 匹配
          name: config

---
apiVersion: v1
kind: Service
metadata:
  name: spring-boot-demo
  namespace: default
  labels:
    app: spring-boot-demo
spec:
  ports:
    - name: port
      port: 80
      protocol: TCP
      targetPort: 8080
  selector:
    app: spring-boot-demo
  type: ClusterIP

3. Use the following command to create a deployment with the configuration mounted:

kubectl apply -f spring-boot-demo.yaml

4. Use the following command to enter the container to check whether it is mounted to the configured directory:

# 查看pod
kubectl get pod -n default
# 进入容器
kubectl exec -it spring-boot-demo-76bd6c8857-kwss6  bash

5. configMap content of mounted 060e8101e29b6d will be automatically updated

configMap used in the volume is updated, the projected keys will eventually be updated. kubelet configMap is the latest during each periodic synchronization. However, kubelet uses its local cache to obtain the current value of configMap The type of cache can be configured by KubeletConfiguration structure ConfigMapAndSecretChangeDetectionStrategy field.

configMap can realize content dissemination through watch operation (default form), TTL-based caching can also be realized, and all requests can be redirected directly to the API server. Therefore, from configMap is updated, until the new primary key is projected to the Pod, this time span may be kubelet the synchronization period of 060e8101e29c64 plus the propagation delay of the cache. The propagation delay here depends on the selected cache type (corresponding to the propagation delay of the watch operation, the TTL duration of the cache, or 0, respectively).

configMap used by 160e8101e29ca1 as environment variables will not be automatically updated. To update these data requires restarting the Pod.

Reference documents:

k8s official website

spring boot official website