AWS ECS instance missing `ecs.capability.efsAuth` attribute – Debian

I have a custom ECS AMI, running Debian 10. I launch the ECS-Agent as a container, as suggested in the docs here. Everything works fine.

Recently, I was asked to integrate EFS into the cluster, so that containers running within specific tasks would have access to shared, persistent storage.

I added the efs-utils package to the AMI build, as documented in the git repo. The instances themselves now automatically mount to EFS on boot, and users on the instances can read/write to the EFS mount.

However, tasks configured to use the efsVolumeConfiguration parameter in the task volume definition fail to get placed; the good old Container instance missing required attribute error.

Because the instances themselves have no problem mounting to EFS on boot, I’ve implemented a workaround using regular docker volumes, so the containers running in the task mount EFS on the host via normal docker volume, but I’d prefer to have the ECS -> EFS integration working properly.

When I run the ECS-CLI check-attributes command against any of the instances in my cluster I get:

ecs-cli check-attributes --task-def my-task --container-instances my-container-instance-id --cluster my-ecs-cluser
Container Instance                    Missing Attributes
my-container-instance-id  ecs.capability.efsAuth

And indeed, in the console, when I go cluster->instances->specific-instance->actions->view/edit attributes, all of the ecs.capability.xxx contain empty values.

When do these values get populated? How should I augment the AMI build so that these values get populated with the proper values?

Please let me know if you need any additional information.
Thanks in advance!