When “AssumeRole” Fails Silently: Fixing CodePipeline with CloudWatch Logs Permissions

When “AssumeRole” Fails Silently: Fixing CodePipeline with CloudWatch Logs Permissions

Problem

You get this maddening AWS CodePipeline error:

InvalidStructureException: 
CodePipeline is not authorized to perform 
AssumeRole on role 
arn:aws:iam::[your account number]:
role/CodePipelineServiceRole

You check the trust relationship, confirm the pipeline role is assumed correctly, but the error doesn’t go away. What’s really happening is that the pipeline is failing to log its activity because the role lacks basic CloudWatch Logs permissions. That failure cascades into misleading errors during execution.

Clarifying the Issue

CodePipeline tries to create and write to CloudWatch Logs automatically during execution. If your pipeline's IAM role can't create a log group or stream, the service may fail silently or throw unrelated errors, like unauthorized AssumeRole. That’s what makes this tricky—you're not just dealing with trust policies. You're dealing with runtime logging gaps.

Why It Matters

Without these log permissions, debugging becomes a guessing game. Worse, your pipeline's actual functionality may be working fine—the issue is just that it can’t record what it's doing. Fixing the IAM policy ensures you get usable logs and clear visibility, which is essential for long-term reliability and security auditing.

Key Terms

• CodePipelineServiceRole – The role that CodePipeline uses to act on your behalf.
• CloudWatch Logs – The AWS service for storing and viewing logs generated by AWS services.
• AssumeRole – Grants temporary access for one AWS service to operate under another IAM role.
• InvalidStructureException – A vague but common CodePipeline error when required IAM permissions are missing.

Steps at a Glance

1. Open the IAM role used by your CodePipeline.
2. Edit the role’s inline or attached policies.
3. Add permissions for CloudWatch Logs actions.
4. Specify the correct log group ARNs for your pipeline.
5. Save changes and rerun your pipeline.

Detailed Steps

1. Open the IAM role used by your CodePipeline.

Go to the AWS Management Console, navigate to IAM → Roles, and locate the role named something like CodePipelineServiceRole-[your pipeline name].

2. Edit the role’s inline or attached policies.

Click on the role, then either edit the inline policy or attach a new one. You’ll be adding logging permissions directly here.

3. Add permissions for CloudWatch Logs actions.

Insert the following into your policy document (replace placeholders with your real data):

JSON

{
  "Effect": "Allow",
  "Action": [
    "logs:CreateLogGroup",
    "logs:CreateLogStream",
    "logs:PutLogEvents"
  ],
  "Resource": [
    "arn:aws:logs:us-east-2:[your account number]:log-group:/aws/codepipeline/[your pipeline name]",
    "arn:aws:logs:us-east-2:[your account number]:log-group:/aws/codepipeline/[your pipeline name]/*"
  ]
}

4. Specify the correct log group ARNs for your pipeline.

Make sure your Resource values match the region and naming pattern of your pipeline log group. This keeps the policy scoped and secure.

5. Save changes and rerun your pipeline.

Apply the policy update, go back to CodePipeline, and trigger a manual run. If logging was the issue, the error will vanish—and now you’ll see proper logs in CloudWatch.

Conclusion

Aaron, this is one of those AWS edge cases where the system punishes you for something totally unrelated to the error message. But now you know—if AssumeRole fails without a clear cause, check your CloudWatch Logs permissions. It’s a small fix that unlocks big visibility. 

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