AWS
IAMConcurrentModification - IAM Concurrent Modification
Getting an **IAMConcurrentModification** error means multiple requests to modify the same IAM entity are being processed simultaneously, causing a conflict—you need to wait for the current operation to complete before retrying. This client-side error (4xx) happens when AWS detects concurrent modification attempts. Most common when simultaneous policy updates occur, but also appears when concurrent role modifications happen, multiple users update the same entity, race conditions occur in updates, or overlapping modification requests are made.
#Common Causes
- →Identity: IAM entity concurrent modification conflict. Service Control Policy (SCP) enforces modification ordering.
- →Network: VPC endpoint IAM modification restrictions. Simultaneous modification requests.
- →Limits: Simultaneous policy updates. Concurrent role modifications. Multiple users updating same entity. Race condition in updates. Overlapping modification requests.
✓Solutions
- 1Step 1: Diagnose - Check entity state: Verify entity exists: aws iam get-user --user-name USER_NAME. Check if entity is in use: aws iam list-attached-user-policies --user-name USER_NAME.
- 2Step 2: Diagnose - Wait for current operation: Check if operation is in progress. Review CloudTrail logs for recent modifications. Wait 5-30 seconds before retry.
- 3Step 3: Diagnose - Implement retry with backoff: Use exponential backoff: delay=1, then 2, 4, 8 seconds. Retry up to 5 times. Check error code is IAMConcurrentModification.
- 4Step 4: Fix - Retry after delay: Wait 5-10 seconds. Retry the modification request. If still fails, wait longer and retry.
- 5Step 5: Fix - Use conditional updates or implement retry logic: Check entity state before modifying. Use exponential backoff retry logic. Or use conditional updates if available. Avoid concurrent modifications.
</>Code Examples
Retry IAM Operation with Exponential Backoff
1#!/bin/bash
2USER_NAME="my-user"
3NEW_PATH="/updated/"
4
5echo "=== Retrying IAM Operation with Exponential Backoff ==="
6
7MAX_ATTEMPTS=5
8DELAY=1
9ATTEMPT=1
10
11while [ ${ATTEMPT} -le ${MAX_ATTEMPTS} ]; do
12 echo "\nAttempt ${ATTEMPT} of ${MAX_ATTEMPTS}"
13
14 RESULT=$(aws iam update-user \
15 --user-name ${USER_NAME} \
16 --new-path ${NEW_PATH} 2>&1)
17
18 if [ $? -eq 0 ]; then
19 echo "✓ Operation succeeded on attempt ${ATTEMPT}"
20 exit 0
21 else
22 # Check if error is ConcurrentModification
23 if echo "${RESULT}" | grep -q "ConcurrentModification"; then
24 if [ ${ATTEMPT} -lt ${MAX_ATTEMPTS} ]; then
25 echo "✗ Concurrent modification detected (IAMConcurrentModification)"
26 echo "Retrying in ${DELAY}s..."
27 sleep ${DELAY}
28 DELAY=$((DELAY * 2))
29 ATTEMPT=$((ATTEMPT + 1))
30 else
31 echo "✗ Operation failed after ${MAX_ATTEMPTS} attempts"
32 exit 1
33 fi
34 else
35 echo "✗ Operation failed with different error"
36 echo "${RESULT}"
37 exit 1
38 fi
39 fi
40doneCheck Entity State Before Modification
1#!/bin/bash
2USER_NAME="my-user"
3
4echo "=== Checking Entity State ==="
5echo "User: ${USER_NAME}"
6
7# Verify entity exists
8USER_INFO=$(aws iam get-user --user-name ${USER_NAME} 2>&1)
9
10if [ $? -eq 0 ]; then
11 echo "✓ User exists"
12
13 # Check if entity is in use
14 echo "\n=== Checking User Dependencies ==="
15 POLICY_COUNT=$(aws iam list-attached-user-policies --user-name ${USER_NAME} \
16 --query 'length(AttachedPolicies)' \
17 --output text)
18
19 echo "Attached policies: ${POLICY_COUNT}"
20
21 echo "\n=== Safe to Modify ==="
22 echo "Entity state checked, proceed with modification"
23else
24 echo "✗ User not found"
25 echo "Error: ${USER_INFO}"
26fiSimple Retry After Delay
1#!/bin/bash
2USER_NAME="my-user"
3NEW_PATH="/updated/"
4
5echo "=== Simple Retry After Delay ==="
6
7# First attempt
8echo "Attempting modification..."
9RESULT=$(aws iam update-user \
10 --user-name ${USER_NAME} \
11 --new-path ${NEW_PATH} 2>&1)
12
13if [ $? -ne 0 ]; then
14 if echo "${RESULT}" | grep -q "ConcurrentModification"; then
15 echo "✗ Concurrent modification detected (IAMConcurrentModification)"
16 echo "Waiting 10 seconds before retry..."
17
18 sleep 10
19
20 echo "\nRetrying modification..."
21 aws iam update-user \
22 --user-name ${USER_NAME} \
23 --new-path ${NEW_PATH}
24
25 if [ $? -eq 0 ]; then
26 echo "\n✓ Operation succeeded on retry"
27 else
28 echo "\n✗ Operation failed on retry"
29 fi
30 else
31 echo "✗ Different error occurred"
32 echo "${RESULT}"
33 fi
34else
35 echo "✓ Operation succeeded on first attempt"
36fi↗Related Errors
Provider Information
This error code is specific to AWS services. For more information, refer to the official AWS documentation.