How to correctly deploy Next Js applications in kubernetes cluster with environments variables

Question

I need my Next js application to read the .env file when deployed to kubernetes. What I do for this:

1. As we know, in order for the next js application to read the .env file, this file must already be in the root folder of the application, before the "npm run build" command. So I create a docker file with this instruction "CMD npm run build; npm run start" so that when kubernetes deploy the container, it first does "npm run build" and after "npm run start".

---

FROM node:lts
WORKDIR /app
COPY . .
RUN npm install
RUN groupadd -g 1001 -r nodejs
RUN useradd -u 1001 -r nextjs
RUN mkdir -p /app/.next/cache/images && chown nextjs:nodejs /app/.next/cache/images
RUN chown -R nextjs /app/.next
VOLUME /app/.next/cache/images
USER nextjs
EXPOSE 3000
CMD npm run build; npm run start

---

2. When deploying the application with "kubectl apply -f ...", I drop the env file into the root folder of the application using config map.

---

kind: ConfigMap
apiVersion: v1
metadata:
  name: environment-variables
  namespace: {{ .Values.namespace }}
data:
  .env: |-
    CMS_URL=http://192.168.****:13**/
    FRONT_URL=http://192.168.****:32***/
    AUTHORIZATION_SERVER_URL=http://192.168.****:32***
    RESOURCE_SERVER_URL=http://192.168.****:31***
    PORT=3000
    NODE_ENV=production
    NEXT_TELEMETRY_DISABLED=1
    NEXT_PUBLIC_CMS_URL=http://192.168.****:1***/
    NEXT_PUBLIC_FRONT_URL=http://192.168.****:32***/
    NEXT_PUBLIC_AUTHORIZATION_SERVER_URL=http://192.168.****:32***
    NEXT_PUBLIC_RESOURCE_SERVER_URL=http://192.168.****:31***
    NEXT_PUBLIC_PORT=3000
    NEXT_PUBLIC_NODE_ENV=production
    NEXT_PUBLIC_NEXT_TELEMETRY_DISABLED=1

---

apiVersion: apps/v1
kind: Deployment
metadata:
  name: register-next-deployment
  namespace: {{ .Values.namespace }}
  labels:
    app: {{ .Values.name }}
spec:
  replicas: 1
  selector:
    matchLabels:
      app: {{ .Values.name }}
  template:
    metadata:
      labels:
        app: {{ .Values.name }}
    spec:
      imagePullSecrets:
      - name: platformdevvops-registry-key
      containers:
      - name: registernext
        image: {{ .Values.image.repository }}:{{ .Values.image.tag }}
        imagePullPolicy: IfNotPresent
        ports:
          - containerPort: {{ .Values.container.port }}
        volumeMounts:
          - mountPath: /app/.env
            name: environment-variables
            readOnly: true
            subPath: .env
      volumes:
        - name: environment-variables
          configMap:
            name: environment-variables
            items:
              - key: .env
                path: .env

In this way, my application successfully reads the env file. But I don't like this method. Are there other ways to do this? I need my .env file to get into the container during deployment to Kubernetes cluster and be read by the application.