For https://toris.io/2021/06/using-ecs-exec-with-readonlyrootfilesystem-enabled-containers/

ecs-task-definition.json

{
    "volumes": [
        { "name": "var-lib-amazon" },
        { "name": "var-log-amazon" }
    ],
    "containerDefinitions": [
        {
            "name": "task-def-level-workaround",
            "readonlyRootFilesystem": true,
            "image": "alpine:3.13",
            "command": [ "sleep", "1000000" ],
            "mountPoints": [
                {
                    "readOnly": false,
                    "containerPath": "/var/lib/amazon",
                    "sourceVolume": "var-lib-amazon"
                },
                {
                    "readOnly": false,
                    "containerPath": "/var/log/amazon",
                    "sourceVolume": "var-log-amazon"
                }
            ]
        }
    ],
    ~~ snip ~~
}