File-log plugin on AWS ECS?

I am running Kong on AWS ECS (Fargate). The access logs go to /dev/stdout and show up just fine in Cloudwatch.

I tried adding the file-log plugin to a service and am running into issues. The file-log plugin says that it’s created but doesn’t show up in the list of plugins for the service; trying to delete it (by plugin id) doesn’t seem to work (trying to add it again gets a unique constraint violation); also the access logs aren’t being written in json format.

This is a real head-scratcher; any ideas?