Update documentation for ECS_HOST_DATA_DIR and ECS_DATA_DIR envs.

README.md

@@ -136,7 +136,7 @@ additional details on each available environment variable.
 | `ECS_LOGLEVEL`  | <crit> | <error> | <warn> | <info> | <debug> | The level of detail that should be logged. | info | info |
 | `ECS_LOGFILE`   | /ecs-agent.log              | The location where logs should be written. Log level is controlled by `ECS_LOGLEVEL`. | blank | blank |
 | `ECS_CHECKPOINT`   | <true | false> | Whether to checkpoint state to the DATADIR specified below. | true if `ECS_DATADIR` is explicitly set to a non-empty value; false otherwise | true if `ECS_DATADIR` is explicitly set to a non-empty value; false otherwise |
-| `ECS_DATADIR`      |   /data/                  | The container path where state is checkpointed for use across agent restarts. | /data/ | `C:\ProgramData\Amazon\ECS\data`
+| `ECS_DATADIR`      |   /data/                  | The container path where state is checkpointed for use across agent restarts. Note that on Linux, when you specify this, you will need to make sure that the Agent container has a bind mount of `$ECS_HOST_DATA_DIR/data:$ECS_DATADIR` with the corresponding values of `ECS_HOST_DATA_DIR` and `ECS_DATADIR`. | /data/ | `C:\ProgramData\Amazon\ECS\data`
 | `ECS_UPDATES_ENABLED` | <true | false> | Whether to exit for an updater to apply updates when requested. | false | false |
 | `ECS_UPDATE_DOWNLOAD_DIR` | /cache               | Where to place update tarballs within the container. | | |
 | `ECS_DISABLE_METRICS`     | <true | false>  | Whether to disable metrics gathering for tasks. | false | true |
@@ -166,7 +166,7 @@ additional details on each available environment variable.
 | `ECS_AWSVPC_BLOCK_IMDS` | `true` | Whether to block access to [Instance Metadata](http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ec2-instance-metadata.html) for Tasks started with `awsvpc` network mode | `false` | Not applicable |
 | `ECS_AWSVPC_ADDITIONAL_LOCAL_ROUTES` | `["10.0.15.0/24"]` | In `awsvpc` network mode, traffic to these prefixes will be routed via the host bridge instead of the task ENI | `[]` | Not applicable |
 | `ECS_ENABLE_CONTAINER_METADATA` | `true` | When `true`, the agent will create a file describing the container's metadata and the file can be located and consumed by using the container enviornment variable `$ECS_CONTAINER_METADATA_FILE` | `false` | `false` |
-| `ECS_HOST_DATA_DIR` | `/var/lib/ecs` | The source directory on the host from which ECS_DATADIR is mounted. We use this to determine the source mount path for container metadata files in the case the ECS Agent is running as a container. We do not use this value in Windows because the ECS Agent is not running as container in Windows. | `/var/lib/ecs` | `Not used` |
+| `ECS_HOST_DATA_DIR` | `/var/lib/ecs` | The source directory on the host from which ECS_DATADIR is mounted. We use this to determine the source mount path for container metadata files in the case the ECS Agent is running as a container. We do not use this value in Windows because the ECS Agent is not running as container in Windows. On Linux, note that when you specify this, you will need to make sure that the Agent container has a bind mount of `$ECS_HOST_DATA_DIR/data:$ECS_DATADIR` with the corresponding values of `ECS_HOST_DATA_DIR` and `ECS_DATADIR`. | `/var/lib/ecs` | `Not used` |
 | `ECS_ENABLE_TASK_CPU_MEM_LIMIT` | `true` | Whether to enable task-level cpu and memory limits | `true` | `false` |
 | `ECS_CGROUP_PATH` | `/sys/fs/cgroup` | The root cgroup path that is expected by the ECS agent. This is the path that accessible from the agent mount. | `/sys/fs/cgroup` | Not applicable |
 | `ECS_CGROUP_CPU_PERIOD` | `10ms` | CGroups CPU period for task level limits. This value should be between 8ms to 100ms | `100ms` | Not applicable |