What causes "Error: Conflicting configuration arguments"?

Using both 'filename' and 's3_bucket'/'s3_key' in aws_lambda_function resource Specifying both 'image_uri' and 'handler'/'runtime' in container-based Lambda Combining 'image_uri' with 'filename' or S3 deployment in aws_lambda_function

How to fix Error: Conflicting configuration arguments in Terraform

TerraformINTERMEDIATEMEDIUMUpdated Dec 30, 2025· 122 views

Terraform resource configuration often has mutually exclusive arguments where you must choose one option or another, not both. This error occurs when you try to use conflicting options simultaneously in your Terraform code.

Quick fix

Fixes Error: Conflicting configuration arguments

Error: Conflicting configuration arguments

  on main.tf line 5, in resource "aws_lambda_function" "example":
   5:   filename   = "lambda.zip"
   6:   s3_bucket  = "my-bucket"

'filename' and 's3_bucket'/'s3_key' cannot be used together.

Identify which arguments conflict
Choose one deployment method for Lambda
For container-based Lambda, remove runtime and handler
Review the provider documentation for your resource

terraform — error

$Error: Conflicting configuration arguments
  on main.tf line 5, in resource "aws_lambda_function" "example":
   5:   filename   = "lambda.zip"
   6:   s3_bucket  = "my-bucket"
'filename' and 's3_bucket'/'s3_key' cannot be used together.
Error: Conflicting configuration arguments

What this error means

Some Terraform resource arguments cannot be used together. They are mutually exclusive by design because they represent different ways of accomplishing the same goal. When Terraform detects that you've specified two conflicting arguments at the same time, it raises this error because it cannot determine which one you intend to use.

Typical symptoms

Terraform plan or apply command fails immediately with 'Conflicting configuration arguments'
Error message specifies which arguments conflict (e.g., 'filename' and 's3_bucket')
The error occurs before any resources are provisioned
Your HCL configuration looks syntactically correct but contains incompatible options

Common causes

Using both 'filename' and 's3_bucket'/'s3_key' in aws_lambda_function resource
Specifying both 'image_uri' and 'handler'/'runtime' in container-based Lambda
Combining 'image_uri' with 'filename' or S3 deployment in aws_lambda_function
Using both inline and external data source definitions simultaneously
Mixing 'private_key' and 'private_key_openssh' in SSH key configuration
Specifying both 'vpc_config' and 'vpc_security_group_ids' for certain resources
Combining 'root_block_device' and 'ebs_block_device' for the same device

How to fix "Error: Conflicting configuration arguments"

1Identify which arguments conflict

Read the full error message carefully to see which specific arguments conflict. Terraform provides helpful output like:

bash

Error: Conflicting configuration arguments

  on main.tf line 5, in resource "aws_lambda_function" "example":
   5:   filename   = "lambda.zip"
   6:   s3_bucket  = "my-bucket"

'filename' and 's3_bucket'/'s3_key' cannot be used together.

This tells you exactly which options in your resource cannot coexist.

2Choose one deployment method for Lambda

For AWS Lambda, you must choose between local deployment or S3 deployment:

Option 1: Local File Deployment

hcl

resource "aws_lambda_function" "example" {
  filename         = "lambda_function.zip"
  source_code_hash = filebase64sha256("lambda_function.zip")
  function_name    = "my_function"
  role             = aws_iam_role.lambda_role.arn
  handler          = "index.handler"
  runtime          = "nodejs18.x"
}

Option 2: S3 Deployment

hcl

resource "aws_lambda_function" "example" {
  s3_bucket = "my-deployment-bucket"
  s3_key    = "lambda_function.zip"
  function_name = "my_function"
  role           = aws_iam_role.lambda_role.arn
  handler        = "index.handler"
  runtime        = "nodejs18.x"
}

Remove all conflicting arguments and keep only one method.

3For container-based Lambda, remove runtime and handler

If using container images (image_uri), you cannot specify handler and runtime:

hcl

# WRONG - These conflict with image_uri
resource "aws_lambda_function" "example" {
  image_uri = "123456789012.dkr.ecr.us-east-1.amazonaws.com/my-lambda:latest"
  handler   = "index.handler"  # REMOVE THIS
  runtime   = "nodejs18.x"     # REMOVE THIS
}

# CORRECT - Image-based Lambda
resource "aws_lambda_function" "example" {
  image_uri      = "123456789012.dkr.ecr.us-east-1.amazonaws.com/my-lambda:latest"
  function_name  = "my_function"
  role           = aws_iam_role.lambda_role.arn
  package_type   = "Image"
}

Container images define their own entry point and runtime, so these settings are redundant.

4Review the provider documentation for your resource

Each Terraform resource documents which arguments conflict. For example:

For aws_lambda_function:
- filename conflicts with s3_bucket and s3_key
- image_uri conflicts with filename, s3_bucket, handler, and runtime

For AWS EC2 instance:
- root_block_device and ebs_block_device cannot specify the same device

Visit the [AWS Provider documentation](https://registry.terraform.io/providers/hashicorp/aws/latest/docs) and search for your resource to see all conflicting argument pairs listed in the Argument Reference section.

5Use conditional blocks for flexible configurations

If you need to support multiple deployment methods, use variables and conditional blocks:

hcl

variable "deployment_method" {
  type = string
  enum = ["local", "s3", "image"]
}

resource "aws_lambda_function" "example" {
  function_name = "my_function"
  role          = aws_iam_role.lambda_role.arn

  # Local deployment
  filename         = var.deployment_method == "local" ? "lambda.zip" : null
  source_code_hash = var.deployment_method == "local" ? filebase64sha256("lambda.zip") : null
  handler          = var.deployment_method != "image" ? "index.handler" : null
  runtime          = var.deployment_method != "image" ? "nodejs18.x" : null

  # S3 deployment
  s3_bucket = var.deployment_method == "s3" ? "my-bucket" : null
  s3_key    = var.deployment_method == "s3" ? "lambda.zip" : null

  # Image deployment
  image_uri    = var.deployment_method == "image" ? "123456789012.dkr.ecr.us-east-1.amazonaws.com/my-lambda:latest" : null
  package_type = var.deployment_method == "image" ? "Image" : "Zip"
}

This allows one Terraform module to support all deployment methods while avoiding conflicts.

6Validate your configuration with terraform validate

After removing conflicting arguments, validate your configuration:

bash

terraform validate

This performs syntax and argument validation without connecting to AWS. If this command succeeds, you've resolved the conflict.

Advanced notes

Understanding AWS Lambda deployment options:

1. Zip vs Container: AWS Lambda supports two package types:
- Zip: Traditional .zip deployment with handler and runtime specified
- Image: Container image with everything defined in the Dockerfile

2. Code source flexibility: Within Zip deployments, you can source code from:
- Local file system (filename)
- S3 bucket (s3_bucket + s3_key)
- Lambda code archive (if using AWS Console)

You MUST choose exactly one source method.

3. Common patterns:
- Development: Use local file with filebase64sha256() for hash
- CI/CD: Upload to S3 first, reference from Terraform
- Containers: Use ECR image with package_type = "Image"

4. Module reusability: Create separate Terraform modules for each deployment pattern to avoid complexity:
- modules/lambda-zip-local
- modules/lambda-zip-s3
- modules/lambda-image

5. Source code hash considerations: When using filename, always compute the hash to trigger updates when code changes. The source_code_hash field should change whenever your code changes to force Lambda to update. Use:
- filebase64sha256() for local files
- source_code_hash = var.source_hash when building externally

This ensures Lambda stays in sync with your code changes.

Frequently asked questions

What does "Error: Conflicting configuration arguments" mean?: Some Terraform resource arguments cannot be used together. They are mutually exclusive by design because they represent different ways of accomplishing the same goal. When Terraform detects that you've specified two conflicting arguments at the same time, it raises this error because it cannot determine which one you intend to use.
How do I fix "Error: Conflicting configuration arguments"?: Terraform resource configuration often has mutually exclusive arguments where you must choose one option or another, not both. This error occurs when you try to use conflicting options simultaneously in your Terraform code.
What causes "Error: Conflicting configuration arguments"?: Using both 'filename' and 's3_bucket'/'s3_key' in aws_lambda_function resource Specifying both 'image_uri' and 'handler'/'runtime' in container-based Lambda Combining 'image_uri' with 'filename' or S3 deployment in aws_lambda_function
Is the "Error: Conflicting configuration arguments" error serious?: It is a medium-severity error — more of a blocker than a risk. The steps above resolve it.

Official resources & further reading

📚Terraform Official Documentation
📖
AWS Lambda Function Resource Documentation(Official Docs)
HashiCorp Discuss: Conflicting configuration arguments with AWS Lambda
📖
Terraform Conditional Expressions Guide(Official Docs)
📖
AWS Provider: aws_lambda_function resource overview(Official Docs)