diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 42e3aa342511d8efafca85c924739c4e6858bb43..60969f0e2d1daba7c494a479614ce6a5f19c2309 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -26,6 +26,7 @@ variables:
   GIT_AUTHOR_EMAIL: "gitlab@runner"
   NUM_SERVER_TO_KEEP: 1
   NUM_IMAGE_TO_KEEP: 30
+  TIMESTAMP_REGEXP: '[0-9]{4}-[0-9]{2}-[0-9]{2}T[0-9]{6}'
   PKR_VAR_root_ssh_key: "ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBAFqqWgmYpEaGtHBeTu27ntVJpYjwq/x5aBefrvfhk8Z9lE3cuZ26vJ9n/9tGE4Zn2Pew1mpZgi6PzfJ3vMt8yA= root@master"
   DEV_KEY: "ssh-rsa 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 louistw@uab.edu"
 
@@ -386,7 +387,7 @@ cleanup:
   script:
     - |
       SERVER_TO_BE_DELETE=($(openstack server list --name $OOD_INSTANCE_NAME --sort-column Image --sort-descending -f value -c ID | awk -v NSTK=$NUM_SERVER_TO_KEEP '{count++} {if (count>NSTK) print}'))
-      IMAGE_TO_BE_DELETE=($(openstack image list --sort-column Name --sort-descending -f value -c Name -c ID | awk -v NITK=$NUM_IMAGE_TO_KEEP '/ ood-[[:digit:]]{8}$/ {count++} {if (count>NITK) print $1}'))
+      IMAGE_TO_BE_DELETE=($(openstack image list --sort-column Name --sort-descending -f value -c Name -c ID | awk -v NITK=$NUM_IMAGE_TO_KEEP -v REGEX=ood-$TIMESTAMP_REGEX '{if ($0 ~ REGEX) result[count++] = $1} END {for(i=NITK;i<count;i++) print result[i]}'))
       for svr in ${SERVER_TO_BE_DELETE[@]}; do
         openstack server delete ${svr}
       done