Allow the setting of instance is for file download

If set override picking the first instance in the list this can be useful if
there is more than one cluster in the environment or you are working on a
specific instance.

bin/ecs/file-download

@@ -11,6 +11,7 @@ usage() {
   echo "Usage: $(basename "$0") [OPTIONS]" 1>&2
   echo "  -h                     - help"
   echo "  -i <infrastructure>    - infrastructure name"
+  echo "  -I <instance>          - instance id"
   echo "  -e <environment>       - environment name (e.g. 'staging' or 'prod')"
   echo "  -s <source>            - Source"
   echo "  -t <local target>      - local target"
@@ -35,11 +36,14 @@ fi
 
 RECURSIVE=0
 
-while getopts "i:e:s:t:rh" opt; do
+while getopts "i:I:e:s:t:rh" opt; do
   case $opt in
     i)
       INFRASTRUCTURE_NAME=$OPTARG
       ;;
+    I)
+      INSTANCE_ID=$OPTARG
+      ;;
     e)
       ENVIRONMENT=$OPTARG
       ;;
@@ -91,12 +95,11 @@ fi
 echo "==> Finding ECS instance..."
 
 INSTANCES=$(aws ec2 describe-instances --filters Name=instance-state-code,Values=16 Name=tag:Name,Values="$INFRASTRUCTURE_NAME-$ENVIRONMENT*")
-INSTANCE_ID=$(echo "$INSTANCES" | jq -r '.Reservations[0].Instances[0].InstanceId' )
+INSTANCE_ID=${INSTANCE_ID:-$(echo "$INSTANCES" | jq -r '.Reservations[0].Instances[0].InstanceId' )}
 INSTANCE_NAME=$(echo "$INSTANCES" | jq -r '.Reservations[0].Instances[0].Tags[] | select(.Key == "Name") | .Value')
 
 echo "==> uploading from '$INSTANCE_NAME' (id: $INSTANCE_ID) to S3.."
 
-
 aws ssm start-session \
   --target "$INSTANCE_ID" \
   --document-name "$INFRASTRUCTURE_NAME-$ENVIRONMENT-s3-upload" \