The private network range is defined by IETF (Ref: https://tools.ietf.org/html/rfc1918) and adhered to by all cloud providers. The supported internal IP Address ranges are:
1. 24-bit block 10.0.0.0/8 (16777216 IP Addresses)
2. 20-bit block 172.16.0.0/12 (1048576 IP Addresses)
3. 16-bit block 192.168.0.0/16 (65536 IP Addresses)
10.0.0.0/8 gives you the most extensive range - 16777216 IP Addresses.

Stackdriver logging allows filtering of logs based on resource (i.e. Cloud Spanner) then sub category of granting access will provide info as to when a role was granted to the user.

A and B are not correct because this will make the application temporarily unavailable to users.
C is not correct because to roll back, you'll need to redeploy the previous deployment because the app was overwritten with the same version number. Therefore this takes longer than a rollback using method D.
D is correct because this makes sure there is no downtime and you can roll back the fastest.
https://cloud.google.com/appengine/docs/admin-api/migrating-splitting-traffic

The type of traffic that you need your load balancer to handle is another factor in determining which load balancer to use:
HTTP and HTTPS traffic: External HTTP(S) Load Balancing / Regional external HTTP(S) / load balancer Internal HTTP(S) Load Balancing TCP traffic: TCP Proxy Load Balancing / External TCP/UDP Network Load Balancing / Internal TCP/UDP Load Balancing / SSL traffic: SSL Proxy Load Balancing UDP traffic: External TCP/UDP Network Load Balancing / Internal TCP/UDP Load Balancing

https://cloud.google.com/storage/docs/gsutil/commands/cp#parallel-composite-uploads_1 Warning: Parallel composite uploads should not be used with NEARLINE, COLDLINE, or ARCHIVE storage class buckets, because doing so incurs an early deletion charge for each component object.
Warning: Parallel composite uploads should not be used in buckets that have a retention policy, because the component pieces cannot be deleted until each has met the bucket's minimum retention period.