How to Fix Terraform Permission Denied on Vercel

As a Senior DevOps Engineer, encountering “Permission Denied” errors during infrastructure provisioning is a familiar challenge, especially when integrating tools like Terraform into modern CI/CD pipelines. When this surfaces in the context of Vercel deployments, it points to a specific set of considerations related to environment isolation and credential management.

This guide will walk you through diagnosing and resolving “Terraform Permission Denied” errors when Terraform commands are executed as part of your Vercel build process.

Troubleshooting Guide: Terraform Permission Denied on Vercel

1. The Root Cause

The “Permission Denied” error when Terraform runs on Vercel stems from a fundamental mismatch: The isolated Vercel build environment lacks the necessary cloud provider credentials and associated IAM permissions to perform the actions defined in your Terraform configuration.

Here’s a breakdown:

  • Vercel’s Build Environment: Vercel deploys your frontend applications within transient, isolated container environments. By design, these containers have no inherent access to your cloud provider accounts (AWS, GCP, Azure, etc.) or their APIs.
  • Terraform’s Requirement: Terraform, as an Infrastructure as Code (IaC) tool, needs authenticated access to your target cloud provider to create, modify, or destroy resources. It relies on credentials (e.g., access keys, service account keys, environment variables pointing to an IAM role) to authenticate.
  • The Disconnect: When your Vercel build process (e.g., via a custom build script or vercel.json command) attempts to execute terraform apply or terraform plan, Terraform tries to authenticate. If the necessary environment variables for your cloud provider’s credentials are not correctly supplied or if the underlying IAM user/role associated with those credentials lacks the required permissions for the resources being managed, you will hit a “Permission Denied” error.

In essence: Vercel doesn’t know who Terraform is supposed to be, or what it’s allowed to do, in your cloud account.

2. Quick Fix (CLI)

The most direct way to provide Terraform with the necessary credentials in a Vercel build is by setting environment variables using the Vercel CLI. This ensures they are securely injected into your build environment.

Steps:

  1. Identify Required Environment Variables:

    • AWS: AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY, (optionally AWS_SESSION_TOKEN if using temporary credentials, and AWS_REGION if not set in Terraform configuration).
    • GCP: GOOGLE_CREDENTIALS (JSON string of a service account key) or GOOGLE_APPLICATION_CREDENTIALS (path to a service account key file, less common for direct env var injection).
    • Azure: ARM_CLIENT_ID, ARM_CLIENT_SECRET, ARM_TENANT_ID, ARM_SUBSCRIPTION_ID.

  2. Add Environment Variables via Vercel CLI: Navigate to your project directory in the terminal and use the vercel env add command. Remember to specify the --git flag to make them available to your Git-connected deployments.

    Example for AWS:

    # Add AWS Access Key ID
vercel env add AWS_ACCESS_KEY_ID
# When prompted, paste your AWS_ACCESS_KEY_ID value
# Choose "Production", "Preview", and "Development" environments as needed.

# Add AWS Secret Access Key
vercel env add AWS_SECRET_ACCESS_KEY
# When prompted, paste your AWS_SECRET_ACCESS_KEY value
# Choose "Production", "Preview", and "Development" environments as needed.

# (Optional) Add AWS Region if not hardcoded in Terraform or using provider default
vercel env add AWS_REGION
# When prompted, enter your default AWS region (e.g., "us-east-1")
# Choose "Production", "Preview", and "Development" environments as needed.

    Important Considerations:

    • Security: Never hardcode sensitive credentials directly in your vercel.json or source code. Vercel’s environment variables are encrypted and securely injected.
    • Least Privilege: Ensure the AWS IAM user, GCP Service Account, or Azure Service Principal associated with these credentials has only the minimum necessary permissions required for your Terraform configuration. Granting * (all permissions) is a severe security risk.

3. Configuration Check

After providing credentials via environment variables, you need to verify that your Vercel project and Terraform configuration are set up to properly utilize them.

3.1 Vercel Project Settings

  1. Vercel Dashboard: Go to your project settings in the Vercel dashboard.
  2. Environment Variables: Navigate to the “Environment Variables” section.
  3. Verify Presence: Ensure the environment variables you added (e.g., AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY) are present and configured for the correct “Environments” (e.g., Production, Preview, Development). If you’re building a preview deployment, make sure they are enabled for “Preview”.

3.2 Terraform Configuration (.tf files)

Ensure your Terraform provider block is configured to read credentials from environment variables, which is the standard and recommended practice for CI/CD.

Example for AWS (providers.tf or main.tf):

# AWS Provider Configuration
provider "aws" {
  region = var.aws_region # Can be set via AWS_REGION env var
}

variable "aws_region" {
  description = "AWS region"
  type        = string
  default     = "us-east-1" # Or omit default if always relying on env var
}
  • Crucially: You should not have access_key or secret_key explicitly defined within your provider "aws" block in your .tf files, as this can lead to security vulnerabilities and conflicts with environment variables. Terraform will automatically pick up AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY from the environment if they are present.
  • GCP Provider Example: The GCP provider also prioritizes environment variables (GOOGLE_CREDENTIALS or GOOGLE_APPLICATION_CREDENTIALS). 
    provider "google" {
  project = var.gcp_project_id
  region  = var.gcp_region
  # credentials = file("path/to/key.json") # AVOID this in Vercel, use env vars
}
variable "gcp_project_id" { type = string }
variable "gcp_region" { type = string }

3.3 IAM Policy Verification (Cloud Provider)

Even if credentials are passed correctly, a “Permission Denied” error often means the identity associated with those credentials lacks the necessary permissions for a specific action.

  1. Identify the IAM Entity: Determine which AWS IAM user/role, GCP Service Account, or Azure Service Principal corresponds to the credentials you’re using.
  2. Review IAM Policy:
    • Go to your cloud provider’s IAM console.
    • Inspect the permissions policy attached to that entity.
    • Look for specific Allow statements for the resources and actions your Terraform configuration is trying to perform (e.g., s3:CreateBucket, lambda:CreateFunction, ec2:RunInstances).
    • Principle of Least Privilege: Ensure the policy grants only the permissions absolutely required by your Terraform configuration. If Terraform is trying to create an S3 bucket and you see s3:CreateBucket is explicitly denied or simply not allowed, that’s your culprit.

4. Verification

After implementing the fixes, trigger a new Vercel deployment to verify the issue is resolved.

  1. Push Changes: Commit any changes (if you modified vercel.json or .tf files) and push to your Git repository connected to Vercel.
  2. Monitor Vercel Logs:
    • Go to your Vercel project dashboard and navigate to the “Deployments” section.
    • Click on the latest deployment and watch the “Build Logs.”
    • Look for the output of your Terraform commands (terraform init, terraform plan, terraform apply).
    • If successful, you should see Terraform performing its actions without permission errors.
  3. Cloud Provider Console:
    • Once the Vercel deployment completes successfully, log into your cloud provider’s console.
    • Verify that the resources provisioned or modified by Terraform are in the expected state.

Still encountering errors?

  • Examine the Exact Error Message: The “Permission Denied” message from Terraform/your cloud provider is often highly specific (e.g., “User is not authorized to perform: s3:PutObject on resource: arn:aws:s3:::my-bucket/*”). This detail is crucial for pinpointing the missing IAM permission.
  • Vercel Build Environment Debugging: If necessary, you can add echo commands in your vercel.json’s build command (or custom build script) to confirm environment variables are present (e.g., echo $AWS_REGION). Be extremely careful not to echo sensitive secrets.
  • Local Reproduction: Temporarily try to run terraform plan or terraform apply locally using the exact same credentials (set as local environment variables) that you provided to Vercel. This can help isolate if the issue is Vercel-specific or related to the credentials/IAM policy themselves.

By systematically checking your Vercel environment variables, Terraform configuration, and cloud provider IAM policies, you can effectively troubleshoot and resolve “Terraform Permission Denied” errors, ensuring your IaC works seamlessly within your Vercel deployment pipeline.

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