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tfmerge

A tool to merge multiple Terrafrom state files into one.

Usage

Given you have an initialized Terraform working directory (abbr. wd) (create one and run terraform init in it if not existed yet). The state file in wd will be used as the base state file (i.e. the lineage will be reserved, and the serial will be incremented). Meanwhile, you have other three state files to be merged: state1, state2, state3, where the module and resource addresses among these state files together with the base state file have no overlaps.

tfmerge helps you merging these state files into the base state file by simply running tfmerge -o terraform.tfstate state1 state2 state3 within the wd.

If your wd is using a non-local backend, you'll need to manually upload the merged state file via terraform state push.

How

The process is inspired by https://support.hashicorp.com/hc/en-us/articles/4418624552339-How-to-Merge-State-Files

tfmerge will simply do followings:

  • Run terraform state pull to retrieve the base state file, works for both local and non-local backends. Especially, the output can be an empty string if there is no state file in the working directory, in this case a new state file will be created with a new lineage.
  • Run terraform state list on the base state file and the to-be-merged state files, to list all the items to be moved. Meanwhile, ensure there is no resource/module address overlap.
  • Copy all the state files to a temporary directory, to avoid mutation on existing state files.
  • Repeatedly run terraform state mv -state-out=<base statefile copy> -state=<statefile1 copy> <item address> <item address>
  • Return the merged base state file

Reference