Do you want to use Google Storage for your image uploads? Here are the steps:
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Set a default Google project if you don’t have one.
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Get a developer key.
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Create a bucket by going here. Enter a unique name and select a default storage class (I used multi-regional within the US).
Now we need to configure the Discourse instance. Go to settings, and add a filter for S3. Then make the changes below:
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Check the “
enable s3 backups” checkbox if you want to activate manual or automated backups -
Enter the desired bucket name created above in “
s3 backup bucket” ifenable s3 backupsis checked -
Paste in both “
Access Key ID” and “Secret Access Key” in their respective text fields (these were generated when the developer key was created) -
In
s3_endpoint, paste in the below endpoint:https://storage.googleapis.com
That’s it! Try uploading an image - it should all work magically 
To ‘serve’ images directly from your domain, follow the steps below:
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Make sure your bucket is accessible publicly. It needs to set up using object level permissions though
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Set up a load balancer if you don’t already have one. For the backend, create a backend bucket, point it to the storage bucket created above, enable CDN, and connect it
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For the URL map, create two rules. Hosts for both need to be
*; paths need to be/original/*and/optimized/*; and the backend needs to point to the backend bucket - save the settings -
In Discourse settings, change the
s3 cdn url toyour domain - make sure this ties in with how your load balancer rule has been set up
That’s it - the images should now come from www.yourdomain.com/
Backups are now possible, as @tuanpembual thankfully pointed out in this post . Essentially, you need to:
- Go to your project in Google Cloud Console
- Select Storage
- Select your bucket
- Go to the permissions tab
- Add new permission, fill your service account email with your account. for roles, select Storage Legacy Object Owner
- Save and done.