You use one custom machine image across multiple managed instance groups; each group needs a different set of configuration values. Using only Compute Engine built-in features, where should per-deployment configuration be stored?

Instance metadata is the correct choice because it allows you to store custom key-value pairs that are unique to each instance template within a managed instance group. This enables each group to receive its specific configuration values without modifying the shared custom machine image. These values are accessible from within the VM at boot time or runtime. Writing to the VM's persistent disk is not ideal as it requires modifying the disk directly, which is less dynamic. Cloud Bigtable is a NoSQL database and overkill for simple per-deployment configuration values. While a startup script can use metadata, placing the values directly in the metadata is more direct and manageable for configuration.