backport of commit 3ca74ccca8

website/content/docs/hcp/index.mdx

@@ -47,6 +47,9 @@ Refer to [`hcp_packer_registry`](/packer/docs/templates/hcl_templates/blocks/bui
 
 Packer uses a unique fingerprint for tracking the completion of builds associated to an iteration. By default a fingerprint is automatically generated by Packer during each invocation of `packer build`, unless a fingerprint is manually provided via the `HCP_PACKER_BUILD_FINGERPRINT` environment variable.
 
+In versions before 1.9.0, this fingerprint was computed from the git SHA of the current HEAD in which your template is stored. If you are running builds outside of Git, you would have to set the `HCP_PACKER_BUILD_FINGERPRINT` environment variable prior to invoking `packer build`.
+Starting with Packer 1.9.0, the fingerprint generation does not rely on Git at all, and instead Packer will generate a Unique Lexicographically sortable IDentifier (ULID).
+
 #### Fingerprints and Incomplete Iterations
 
 When you build a template with Packer, there's always a chance that it does not succeed because of a network issue, a provisioning failure, or some upstream error. When that happens, Packer will output the generated fingerprint associated with the incomplete iteration so that you can resume building that iteration using the `HCP_PACKER_BUILD_FINGERPRINT` environment variable; an iteration can be resumed until it is marked as complete. This environment variable is necessary for resuming an incomplete iteration, otherwise Packer will create a new iteration for the build.