Created EMR Cluster Using CloudFormation template but unable to access s3 services on primary node when login through SSH.

Question

I’ve encountered an issue with accessing AWS S3 services from an EMR cluster created using a CloudFormation template. While the cluster is successfully created and configured, and the IAM roles and instance profiles have been correctly attached, the cluster is unable to access S3 services. Here are the details:

**Problem Description**

**Context**:
          I have created an EMR cluster using a CloudFormation template. The cluster creation process completes 
          without errors.

**Issue**: 
          When I log in to the primary node of the cluster via SSH and attempt to access S3, I encounter the error
          "Aws credentials are null".

**Comparison**:
            A cluster created with the same configuration using the AWS Management Console runs smoothly and 
           can access S3 without issues.

**Configuration Details**

1. CloudFormation Template:
The template includes configurations for creating an EMR cluster, service roles, and instance profiles.
The IAM roles and instance profiles used are identical to those used in the Console-based cluster.

2. IAM Roles and Policies:
The roles and instance profiles have the same policies attached as the ones in the Console-created cluster.

3. VPC and Subnet:
The VPC and subnets used are the same as those used when creating the cluster via the Console.

**Troubleshooting Steps Taken**

1. Verified IAM roles and policies to ensure they have appropriate permissions for S3 access.
2. Checked VPC and subnet configurations to confirm they are correct and match those used in the Console-based cluster.
3. Compared instance profiles and roles between the CloudFormation template and the Console-based configuration.****

Thanniru Anil Kumar · Answer

**1. Verify Instance Profile Association**

Ensure that the EC2 instances in the EMR cluster are correctly associated with the IAM instance profile that has the necessary permissions to access S3.

You can verify the IAM instance profile attached to the EMR instances by using the AWS CLI:

```
aws ec2 describe-instances --instance-ids

```

Check if the IamInstanceProfile section is correctly associated with the required role.

**2. Check EMR Cluster Configuration in CloudFormation**

Review the CloudFormation template to ensure that the ServiceRole and InstanceProfile are correctly specified under the AWS::EMR::Cluster resource. The correct attributes should be set like this:

```
ServiceRole: 
JobFlowRole:

```
**3. Inspect Credentials on the Primary Node**

Log in to the primary node and check if the AWS credentials are correctly configured. Run the following command to verify:

```
aws sts get-caller-identity

```
If this command returns an error or no credentials, it indicates that the instance profile is not correctly applied, or there may be a delay in propagating the credentials.

**4. Validate CloudFormation Role and Instance Profile**

Ensure that the CloudFormation stack itself has the necessary permissions to create and attach the correct IAM roles and instance profiles. The role used by CloudFormation should have permissions to use iam:PassRole for the roles being assigned to the EMR instances.

**5. Re-Sync IAM Role on EC2 Instances**

Sometimes, re-syncing the IAM role can resolve issues. You can re-attach the IAM role using the AWS CLI:

```
aws ec2 associate-iam-instance-profile --instance-id  --iam-instance-profile Name=

```
**6. Compare EMR Configurations**

Compare the EMR configurations between the CloudFormation-created and Console-created clusters. Sometimes minor differences in configurations can cause issues.

**7. Check for Instance Metadata Service Version**

Ensure that the EC2 instances have access to the Instance Metadata Service (IMDS). This can be checked using:

```
curl http://169.254.169.254/latest/meta-data/iam/info

```
**8. Review CloudWatch Logs**

Check the CloudWatch logs for the EMR cluster to see if there are any errors or warnings that could provide more insight into the issue.

Created EMR Cluster Using CloudFormation template but unable to access s3 services on primary node when login through SSH.

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