module/init-snippet-attach-ebs-volume: Manually make device name for attached EBS volume.

Due to Linux kernel and Distro changes, an attched EBS volume may not get the specified device name (Ref https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/device_naming.html). Hence logic following may break since specified device does not exist.

This change uses Linux trick to manually setup (if it has not) the device name, so other logic can be static, without guessing which device is it.

Author: Magicloud

modules/init-snippet-attach-ebs-volume/snippet.tpl

@@ -3,6 +3,7 @@ ${init_prefix}
 export AWS_DEFAULT_REGION=${region}
 VOLUME_ID=${volume_id}
 INSTANCE_ID="$(ec2metadata --instance-id)"
+
 echo "${log_prefix} will attach $${VOLUME_ID} via the AWS API in ${region}"
 while ! aws ec2 attach-volume                     \
           --volume-id "$${VOLUME_ID}"     \
@@ -11,8 +12,14 @@ while ! aws ec2 attach-volume                     \
   echo "Attaching command failed to run. Retrying."
   sleep '${wait_interval}'
 done
+echo "${log_prefix} $${VOLUME_ID} attached."
 
-while ! ls '${device_path}'; do
-  sleep '${wait_interval}'
+vol_id="$(echo "$${VOLUME_ID}" | tr -d '-')"
+while sleep '${wait_interval}'; [ ! -e /dev/disk/by-id/*-Amazon_Elastic_Block_Store_$${vol_id} ]; do
+  dev_id="$(ls /dev/disk/by-id/*-Amazon_Elastic_Block_Store_$${vol_id} | head -1)"
+  dev_name="/dev/$(readlink "$${dev_id}" | tr / '\n' | tail -1)"
+  [ "$${dev_name}" == "${device_path}" ] || ln -s "$${dev_name}" "$${device_path}"
+  break
 done
+
 ${init_suffix}