fix(backup): use atomic mv to create backup (#1000)

jenkinsci · May 5, 2024 · 25b329a · 25b329a
1 parent 3f036bd
commit 25b329a
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diff --git a/backup/pvc/bin/backup.sh b/backup/pvc/bin/backup.sh
@@ -5,7 +5,9 @@ set -eo pipefail
 [[ ! $# -eq 1 ]] && echo "Usage: $0 backup_number" && exit 1;
 [[ -z "${BACKUP_DIR}" ]] && echo "Required 'BACKUP_DIR' env not set" && exit 1;
 [[ -z "${JENKINS_HOME}" ]] && echo "Required 'JENKINS_HOME' env not set" && exit 1;
-BACKUP_TMP_DIR=$(mktemp -d)
+
+# create temp dir on the same filesystem with a BACKUP_DIR to be able use atomic mv enstead of copy
+BACKUP_TMP_DIR=$(mktemp -d --tmpdir=${BACKUP_DIR})
 trap "test -d "${BACKUP_TMP_DIR}" && rm -fr "${BACKUP_TMP_DIR}"" EXIT SIGINT SIGTERM
 
 backup_number=$1
@@ -23,12 +25,13 @@ tar --zstd -C "${JENKINS_HOME}" -cf "${BACKUP_TMP_DIR}/${backup_number}.tar.zstd
 
 if [[ "$ret" -eq 0 ]]; then
   echo "Backup was completed without warnings"
-  mv "${BACKUP_TMP_DIR}/${backup_number}.tar.zstd" "${BACKUP_DIR}/${backup_number}.tar.zstd"
 elif [[ "$ret" -eq 1 ]]; then
   echo "Backup was completed with some warnings"
-  mv "${BACKUP_TMP_DIR}/${backup_number}.tar.zstd" "${BACKUP_DIR}/${backup_number}.tar.zstd"
 fi
 
+# atomically create a backup file
+mv "${BACKUP_TMP_DIR}/${backup_number}.tar.zstd" "${BACKUP_DIR}/${backup_number}.tar.zstd"
+
 rm -rf "${BACKUP_TMP_DIR}"
 [[ ! -s ${BACKUP_DIR}/${backup_number}.tar.zstd ]] && echo "backup file '${BACKUP_DIR}/${backup_number}.tar.zstd' is empty" && exit 1;
 

diff --git a/website/content/en/docs/Getting Started/latest/configuring-backup-and-restore.md b/website/content/en/docs/Getting Started/latest/configuring-backup-and-restore.md
@@ -15,6 +15,12 @@ Backup and restore is done by a container sidecar.
 
 ### PVC
 
+#### PVC Storage Size
+
+Please ensure that the size of the PVC (Persistent Volume Claim) is sufficient to accommodate `BACKUP_COUNT` + `1` backup **tar.gz** archives.
+
+The additional **+1** space is necessary to facilitate the creation of backups on the same filesystem and to prevent backup file corruption during copying between different filesystems. For further details, please refer to pr [#1000](https://github.com/jenkinsci/kubernetes-operator/pull/1000).
+
 #### Create PVC
 
 Save to the file named pvc.yaml: