I have a django app running in my Google Compute Engine, and it needs to upload video files to my bucket in Google Cloud Storage. When searching for authentication methods, I found this doc. Under Setting the scope of service account access for instances section, it says I need to enable the Cloud Platform access in the settings when creating the VM. I wonder if it is a must and if there's any other way that I can access my cloud storage bucket from my apps in the compute engine. Because creating a new VM and set up the environment is very time-consuming. Any input would be greatly appreciated. Thanks in advance.
As documented on the page you linked to, to authenticate from Google Compute Engine to Google Cloud Storage, you have several options:
Use VM scopes: this must be set before creating the VM, because scopes are immutable once the VM is created. If you want read-only access, you need to add the scope devstorage.read_only (short form) or https://www.googleapis.com/auth/devstorage.read_only (full path). If you want read-write access, you should use the scope devstorage.read_write (short form) or https://www.googleapis.com/auth/devstorage.read_write (full path).
Note: there's also a feature
gcloud beta compute instances set-scopesto update GCE VM scopes at runtime.
An alternative to using scopes is to use JSON authentication tokens, such as via Service accounts which can be used by Google API client libraries to connect to Google Cloud Storage.