Connecting to an external database from an app deployed in Kubernetes

问题

I'm deploying a Spring Boot app in minikube that connects to a database running on the host. Following the 12 factor app recommendations I use environment variables for the necessary configuration:

SPRING_DATASOURCE_DRIVER_CLASS_NAME=org.postgresql.Driver
SPRING_DATASOURCE_PASSWORD=...
SPRING_DATASOURCE_URL=jdbc:postgresql://<HOST_IP_FROM_K8S>:5432/myservice
SPRING_DATASOURCE_USERNAME=...

The kubernetes docs only show how to set environment variables in the service and deployment .yaml files which I don't want to do. Is there a way to pass environment variables on the command line for minikube or kubectl when I create the deployment? (In Docker I do this with -e.)

Note that the environment variables have to be set before starting the app or it crashes.

回答1:

Following Ansil's comment above I used configmap and secret to pass the configuration like this:

kubectl create secret generic springdatasourcepassword --from-literal=SPRING_DATASOURCE_PASSWORD=postgres
kubectl create secret generic springdatasourceusername --from-literal=SPRING_DATASOURCE_USERNAME=postgres
kubectl create configmap springdatasourcedriverclassname --from-literal=SPRING_DATASOURCE_DRIVER_CLASS_NAME=org.postgresql.Driver
kubectl create configmap springdatasourceurl --from-literal=SPRING_DATASOURCE_URL=jdbc:postgresql://172.18.0.1:5432/bookservice

These are referenced in the deployment.yaml file like this:

env:
- name: GET_HOSTS_FROM
  value: dns
- name: SPRING_DATASOURCE_DRIVER_CLASS_NAME
  valueFrom:
    configMapKeyRef:
      name: springdatasourcedriverclassname
      key: SPRING_DATASOURCE_DRIVER_CLASS_NAME
- name: SPRING_DATASOURCE_URL
  valueFrom:
    configMapKeyRef:
      name: springdatasourceurl
      key: SPRING_DATASOURCE_URL
- name: SPRING_DATASOURCE_PASSWORD
  valueFrom:
    secretKeyRef:
      name: springdatasourcepassword
      key: SPRING_DATASOURCE_PASSWORD
- name: SPRING_DATASOURCE_USERNAME
  valueFrom:
    secretKeyRef:
      name: springdatasourceusername
      key: SPRING_DATASOURCE_USERNAME

A full explanation can be found here.

回答2:

We have no direct option with create subcommand in kubectl to pass the environmental variables.

You may use Helm to customize deployment.

(Example: https://docs.bitnami.com/kubernetes/how-to/deploy-java-application-kubernetes-helm/)

来源：https://stackoverflow.com/questions/55667314/connecting-to-an-external-database-from-an-app-deployed-in-kubernetes