Your Raspberry Pi Doesn’t Need a Role—It Needs a Key: Demystifying S3 Access from a Pi Using Boto3

Your Raspberry Pi Doesn’t Need a Role—It Needs a Key: Demystifying S3 Access from a Pi Using Boto3

A developer recently posted a question on AWS re:Post that hits close to home for many in the Pi and cloud world. He had a Raspberry Pi 4, a Python script using Boto3, and a clear goal: access private .csv files from an S3 bucket. But he hit a wall trying to “do it the right way.”

He avoided root credentials (good move), and after reading AWS’s advice, he assumed the best next step was to create an IAM Role for his Pi. That’s where the confusion set in. IAM roles are powerful—but they don’t apply cleanly to devices living outside the AWS ecosystem.

Let’s clear up that confusion and walk through what you should do when connecting a Raspberry Pi to AWS services like S3.

Roles vs Users: Why Your Pi Can’t Assume a Role (Easily)

IAM roles are designed to be assumed by AWS services like EC2, Lambda, or ECS. Those services are running inside the AWS environment, which allows AWS to securely issue temporary credentials behind the scenes.

Your Raspberry Pi, on the other hand, is just a little edge device in your home or lab. It’s not managed by AWS, so it can’t assume a role unless you implement a credential broker like AWS STS, IoT Core, or Cognito—which is possible but overkill for a single project or hobby setup.

Instead, the most secure and sensible route is to create a dedicated IAM user with programmatic access only and apply a tightly scoped policy that limits it to just the S3 resources it needs.

The Correct Setup: IAM User + Least Privilege Policy

Here’s the quick-start guide to get your Pi reading files from S3 using Boto3:

1. Create an IAM user in the AWS console.

   • Skip console access.
   • Enable programmatic access only.

2. Attach a custom policy that only allows the exact access you need. For example:

json
{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": ["s3:GetObject"],
      "Resource": "arn:aws:s3:::your-bucket-name/path/to/csv/*"
    }
  ]
}

3. Generate access keys for this user (Access Key ID and Secret Access Key).

   • Store them securely.
   • Avoid hardcoding them in your script.

4. Use environment variables on the Raspberry Pi to inject credentials securely (see below).

Setting Up Environment Variables on Your Pi

There are two solid ways to configure credentials securely on your Pi so Boto3 can find them:

Option 1: Environment Variables In your shell profile or script:

bash
export AWS_ACCESS_KEY_ID="your-access-key"
export AWS_SECRET_ACCESS_KEY="your-secret-key"
export AWS_DEFAULT_REGION="us-west-2"

Boto3 will automatically pick these up when you run your script.

Option 2: AWS CLI Credential Store Install the AWS CLI and run:

bash
aws configure

Enter the credentials when prompted, and they’ll be saved in ~/.aws/credentials. Boto3 will find them by default.

This approach avoids hardcoding secrets in your source code—critical if you ever share, back up, or version-control your scripts.

Advanced Route: Temporary Credentials (If You Really Need Them)

If you’re deploying a fleet of Pis or want to rotate credentials automatically, you can explore using AWS IoT Core with X.509 certs, or create a backend service that issues short-lived STS credentials via API. But for a single Pi? That’s like using Kubernetes to run a blinking LED.

Stick with the IAM user and keep the policy tight.

Final Thoughts

Creating an IAM user for your Pi isn’t bad practice—it’s best practice when done right. The danger isn’t in creating a user, it’s in creating one with broad, unchecked access and leaving it to rot. By scoping your permissions to only what’s necessary, rotating keys periodically, and keeping credentials out of your code, you’re operating well within AWS security guidelines.

So to the original poster—and anyone else facing this same moment of IAM identity crisis—don’t sweat it. Your Pi doesn’t need to “assume a role.” It just needs a tiny passport, properly stamped.

Got a Pi talking to AWS? 

I'd love to hear how you’re using it—whether it’s personal, experimental, or production-level. Drop a comment and let us know what you’re building!

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