When mounting S3 buckets on EC2 instances using s3fs, many developers encounter authentication issues when trying to leverage IAM roles instead of static credentials. The s3fs utility doesn't automatically pick up IAM role credentials like AWS CLI tools do.

Before proceeding, ensure:

1. EC2 instance has an IAM role with proper S3 permissions
2. s3fs version 1.82 or higher is installed
3. AWS CLI is configured on the instance
4. Instance metadata service is accessible (usually at 169.254.169.254)

The key solution involves configuring s3fs to use the EC2 instance's metadata service for temporary credentials:

# Install required packages
sudo apt-get install s3fs awscli -y

# Create credential helper script
echo '#!/bin/sh
curl http://169.254.169.254/latest/meta-data/iam/security-credentials/ | xargs -I {} curl http://169.254.169.254/latest/meta-data/iam/security-credentials/{}
' | sudo tee /usr/local/bin/s3fs-iam-helper
sudo chmod +x /usr/local/bin/s3fs-iam-helper

Use this mount command syntax:

sudo s3fs your-bucket-name /mnt/s3bucket \
-o iam_role=auto \
-o url=https://s3.amazonaws.com \
-o use_cache=/tmp \
-o allow_other \
-o umask=000

For persistent mounts, add to /etc/fstab:

s3fs#your-bucket-name /mnt/s3bucket fuse _netdev,iam_role=auto,url=https://s3.amazonaws.com,use_cache=/tmp,allow_other,umask=000 0 0

If mounting fails, check:

1. IAM role permissions (test with AWS CLI first)
2. Metadata service connectivity:
   curl http://169.254.169.254/latest/meta-data/iam/security-credentials/
3. s3fs version (older versions lack IAM role support)
4. Bucket region matches the URL endpoint

For better performance with IAM roles:

- Increase metadata service timeout:
  -o connect_timeout=30
- Use regional endpoints:
  -o url=https://s3.eu-west-1.amazonaws.com
- Implement credential caching:
  -o cred_cache=/var/cache/s3fs

When working with AWS EC2 instances that use IAM roles for authentication, mounting S3 buckets via s3fs requires special configuration. The default s3fs setup expects AWS credentials in a credentials file, but with IAM roles, these credentials are dynamically managed by AWS.

Before proceeding, ensure you have:

• An EC2 instance with an IAM role attached that has S3 access permissions
• s3fs installed on your instance (typically via package manager)
• FUSE (Filesystem in Userspace) installed

The key to making s3fs work with IAM roles is to configure it to use the instance metadata service for credentials. Here's how to do it:

# Install required packages
sudo apt-get install s3fs fuse

# Create mount point
sudo mkdir /mnt/my-s3-bucket

# Mount using IAM role
s3fs my-bucket-name /mnt/my-s3-bucket -o iam_role=auto -o url=https://s3.amazonaws.com -o allow_other

For persistent mounts across reboots, add this to your /etc/fstab:

my-bucket-name /mnt/my-s3-bucket fuse.s3fs _netdev,iam_role=auto,url=https://s3.amazonaws.com,allow_other 0 0

If you encounter permission issues:

1. Verify your IAM role has the necessary S3 permissions
2. Check that your security group allows outbound HTTPS (port 443) connections
3. Ensure the EC2 instance metadata service is accessible (try curl http://169.254.169.254/latest/meta-data/)

For better performance with large files:

s3fs my-bucket-name /mnt/my-s3-bucket -o iam_role=auto -o url=https://s3.amazonaws.com \
-o allow_other -o use_cache=/tmp/s3fs-cache -o enable_noobj_cache

When using IAM roles with s3fs:

• Apply the principle of least privilege to your IAM role
• Consider using bucket policies for additional access control
• Monitor API calls through CloudTrail