feat: backup cron

docker/database-backup/backup-cron-entrypoint

@@ -0,0 +1,32 @@
+#!/bin/sh
+set -eu
+
+: "${BACKUP_CRON:=0 3 * * *}"
+
+case "$BACKUP_CRON" in
+    *"
+"*)
+        echo "BACKUP_CRON must contain a single cron expression." >&2
+        exit 1
+        ;;
+esac
+
+cron_field_count="$(printf "%s\n" "$BACKUP_CRON" | awk '{ print NF }')"
+
+if [ "$cron_field_count" -ne 5 ]; then
+    echo "BACKUP_CRON must contain exactly five fields." >&2
+    exit 1
+fi
+
+mkdir -p /backups
+umask 077
+
+printf "%s /usr/local/bin/backup-database scheduled >> /proc/1/fd/1 2>> /proc/1/fd/2\n" \
+    "$BACKUP_CRON" > /etc/crontabs/root
+
+if [ "${BACKUP_RUN_ON_START:-false}" = "true" ]; then
+    /usr/local/bin/backup-database startup
+fi
+
+echo "Database backup cron configured: $BACKUP_CRON"
+exec crond -f -l 2