Kubernetes, how to correctly setup shared volume permission between php-fpm and nginx

Hey guys, I'm new to kubernetes. Been debugging this thing for the past 2 days, please help..

Currently i'm triyng to deploy laravel app on kuberetes. I have setup 1 deployment yaml containing 2 containers (nginx and php-fpm) and a shared volume.

Here's the full yaml:

apiVersion: v1
kind: Service
metadata:
  name: operation-service
  labels:
    app: operation-service
spec:
  type: NodePort
  selector:
    app: operation
  ports:
  - port: 80
    targetPort: 80
    protocol: TCP
    name: http
  - port: 443
    targetPort: 443
    protocol: TCP
    name: https
  - port: 9000
    targetPort: 9000
    protocol: TCP
    name: fastcgi

---
# Create a pod containing the PHP-FPM application (my-php-app)
# and nginx, each mounting the `shared-files` volume to their
# respective /var/www/ directories.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: operation
spec:
  selector:
    matchLabels:
      app: operation
  replicas: 1
  template:
    metadata:
      labels:
        app: operation
    spec:
      volumes:
        # Create the shared files volume to be used in both pods
        - name: shared-files
          emptyDir: {}

        # Secret containing
        - name: secret-volume
          secret:
            secretName: nginxsecret

        # Add the ConfigMap we declared for the conf.d in nginx
        - name: configmap-volume
          configMap:
            name: nginxconfigmap

      containers:
        # Our PHP-FPM application
        - image: asia.gcr.io/operations
          name: app
          volumeMounts:
            - name: shared-files
              mountPath: /var/www
          ports:
            - containerPort: 9000
          lifecycle:
            postStart:
              exec:
                command: ["/bin/sh", "-c", "cp -r /app/. /var/www"]

        - image: nginx:latest
          name: nginx
          ports:
            - containerPort: 443
            - containerPort: 80
          volumeMounts:
            - name: shared-files
              mountPath: /var/www
            - mountPath: /etc/nginx/ssl
              name: secret-volume
            - mountPath: /etc/nginx/conf.d
              name: configmap-volume

---

apiVersion: networking.k8s.io/v1beta1
kind: Ingress
metadata:
  name: ingress
  annotations:
    nginx.ingress.kubernetes.io/force-ssl-redirect: "true"
    nginx.ingress.kubernetes.io/from-to-www-redirect: "true"
    nginx.ingress.kubernetes.io/proxy-body-size: 100m
spec:
  rules:
  - host: testing.com
    http:
      paths:
      - path: /
        backend:
          serviceName: operation-service
          servicePort: 443

Here's my working nginxconf:

server {
    listen 80;
    listen [::]:80;

    # For https
    listen 443 ssl;
    listen [::]:443 ssl ipv6only=on;
    ssl_certificate /etc/nginx/ssl/tls.crt;
    ssl_certificate_key /etc/nginx/ssl/tls.key;

    server_name testing.com;
    root /var/www/public;
    index index.php index.html index.htm;

    location / {
        try_files $uri $uri/ /index.php$is_args$args;
    }

    location ~ \.php$ {
        try_files $uri /index.php =404;
        fastcgi_pass 127.0.0.1:9000;
        fastcgi_index index.php;
        fastcgi_buffers 16 16k;
        fastcgi_buffer_size 32k;
        fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
        #fixes timeouts
        fastcgi_read_timeout 600;
        include fastcgi_params;
    }

    location ~ /\.ht {
        deny all;
    }

    location /.well-known/acme-challenge/ {
        root /var/www/letsencrypt/;
        log_not_found off;
    }


    error_log /var/log/nginx/laravel_error.log;
    access_log /var/log/nginx/laravel_access.log;
}

After deploying, my app won't load on the web. Turns out nginx log is returning:

[error] 19#19: *64 FastCGI sent in stderr: "PHP message: PHP Fatal error:  Uncaught ErrorException: file_put_contents(/app/storage/framework/views/ba2564046cc89e436fb993df6f661f314e4d2efb.php): failed to open stream: Permission denied in /var/www/vendor/laravel/framework/src/Illuminate/Filesystem/Filesystem.php:185

I know how to setup the volume correctly in local docker, how do i set the shared volume permission in kubernetes correctly?