Here I use bitnami/wordpress image and replace entrypoint.sh inside Docker image.

I also installed curl command which needed for health check during ecs task health check also added HEALTHCHECK

entrypoint.sh has /download-extra.sh

/download-extra.sh installs humanmade/s3-uploads s3 wordpress media offload module and also set s3 bucket/s3 region

/download-extra.sh also change wp-config.php for s3 parameter and activate s3-uploads plugin

Any new plugin can only be installed by /download-extra.sh during container initialization if you don't want to use persistent storage.