fix: docker service update with --detach=false hangs on services wi… (

#104)

* fix: docker service update with `--detach=false` hangs on services with 0 tasks

read more here: docker/cli#627

* refactor: use $(...) notation instead of legacy backticks `...`

* refactor: `tasks_num` variable renamed to `num_tasks`

* refactor: use `-f` for filtering service by name

shepherd

@@ -97,6 +97,11 @@ update_services() {
     else
       logger "Trying to update service $name with image $image" "true"
 
+      num_tasks=$(docker service ls -f "name=$name" | awk 'NR==2{print $4}')
+      if [[ $num_tasks = 0/* ]]; then
+        detach_option="--detach=true"
+      fi
+
       # shellcheck disable=SC2086
       if ! timeout "${TIMEOUT:-300}" docker "${config_flag[@]}" service update "$name" $detach_option $registry_auth $no_resolve_image_flag ${UPDATE_OPTIONS} --image="$image" > /dev/null; then
         logger "Service $name update failed on $hostname!"