AWS IAM Identity Center group membership sync failed "GroupMembershipExistsException when calling CreateGroupMembership"

TL;DR

Treat GroupMembershipExistsException as already-done: check membership before calling CreateGroupMembership in the sync, because the user is already in that Identity Center group and the call is not idempotent. Prove it on one failing hire before rolling it to the rest of hires in the same sync or flow, because this fault repeats identically wherever the same condition holds and a fleet-wide or batch-wide first attempt multiplies the damage when the diagnosis is wrong.

AWS IAM Identity Center group membership sync failed "GroupMembershipExistsException when calling CreateGroupMembership"

Use this when

• You see this exact error or symptom: AWS IAM Identity Center group membership sync failed "GroupMembershipExistsException when calling CreateGroupMembership".
• The failure is in the provisioning path named in the title (HR source, identity provider, and target app), and it repeats on the same action rather than happening once and clearing.
• Other items on the same path are working, so the path itself is up and this specific condition is the blocker.

Not for this skill when

• A different error code, message, or tool is involved. Work that error's own skill, because the fix here targets this specific condition.
• The whole service or platform is down. Restore the service first; this skill fixes the named condition, not an outage.
• You cannot identify one affected item to test on. Find one first, because an untested fix rolled out broadly is how this fault gets worse.

Steps

1. Confirm the fault on one failing hire first and capture the evidence before changing anything: check the provisioning log entry for the one failing user in the identity provider (Okta system log, Entra provisioning logs, or the target app's SCIM log), and record the exact error text, the record or host involved, and the time it happened. Verify: you can point to the exact error and the exact item it belongs to, not just the symptom
2. Treat GroupMembershipExistsException as already-done: check membership before calling CreateGroupMembership in the sync, because the user is already in that Identity Center group and the call is not idempotent. Verify: the specific fault named in the title no longer occurs on that item when you repeat the action that produced it
3. Make the operation idempotent: look the record up by its stable key before creating, adopt or update the existing record when it is the same entity, and log which path was taken. Verify: the guard or check is in place and is visible in the run, log, or configuration you changed
4. Retest end to end: rerun provisioning for that single user (on-demand provisioning or a sync cycle) and confirm the target account exists with the right attributes and status. Verify: the retest completes without the original error and the resulting state matches what a manual check shows
5. Roll the fix out to the rest of hires in the same sync or flow in the same way, watching the first few for the same error, and note the root cause and the change in the run or incident record. Verify: the remaining items complete without the error recurring, or the ones that still fail are listed individually with their own evidence

Variant phrasings

GroupMembershipExistsException when calling CreateGroupMembership fix

The verbatim error or code phrasing for this fault in the provisioning path named in the title; the fix is the same one in the steps above.

AWS IAM Identity Center group membership sync failed

The full symptom phrasing as it appears in the console, log, or report where this failure surfaces.

how to fix AWS IAM Identity Center group membership sync failed

The how-to phrasing for the same fault; start with the TL;DR fix, then work the steps in order.

Compatibility: Okta, Microsoft Entra ID, Google Workspace, AWS IAM Identity Center, SCIM 2.0 targets and Terraform providers as named in the title.

Why it happens

This fault happens because create-style operations are not idempotent in most of these systems, so a retry or a pre-existing record surfaces as a hard conflict instead of a no-op. In this case the condition is the one named in the title, in the provisioning path named in the title (HR source, identity provider, and target app): the receiving or acting side reports the failure faithfully, but the underlying state (a record, a setting, a credential, a file, or a mapping) does not match what that action assumes. Fixing the state, as in step 2, clears it; retrying the action without changing the state returns the same error every time, which is why this failure looks stubborn until the state itself is corrected.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_FzoDPxOFE7J5g0TCoSx4rg