Hi,
Have you looked into the EnforceOrder processor :
https://nifi.apache.org/docs/nifi-docs/components/org.apache.nifi/nifi-standard-nar/1.23.2/org.apach...
Based on your description it should do the job. One thing to keep in mind if you want this to work is what is stating in the description :
"...
[IMPORTANT] In order to take effect of EnforceOrder, FirstInFirstOutPrioritizer should be used at EVERY downstream relationship UNTIL the order of FlowFiles physically get FIXED by operation such as MergeContent or being stored to the final destination.
"
The group identifier will be in this case the value of the fragment.identifier:
${fragment.identifie}
The Order Attribute will be the name of the fragment.index:
fragment.index
If you find this helpful please accept the solution.
Thanks