How to fix Error: Check block assertion failed in Terraform

Examine the check block in your Terraform configuration and identify which assert block failed. The error message will specify the exact check name and the condition that evaluated to false.

check "health_validation" {
  data "http" "endpoint" {
    url = "https://api.example.com/health"
  }

  assert {
    condition     = data.http.endpoint.status_code == 200
    error_message = "API endpoint returned status code: ${data.http.endpoint.status_code}"
  }
}

The error_message tells you exactly why the assertion failed. Use this information to understand what needs to be fixed.

Run terraform plan and check the actual values of the resource or data source being validated in the check block. Compare the actual values to what the assertion expects.

terraform plan -out=plan.tfplan

Look at the plan output for the resource referenced in the check block. Verify:
- Does the resource have the expected attributes?
- Are the attribute values what the assertion expects?
- Is the data source returning the expected values?

Update your Terraform configuration to ensure the resource or data source will satisfy the assertion condition. This is the actual fix—the check is only reporting the problem.

For example, if a check asserts that an AWS load balancer has deletion protection enabled:

resource "aws_lb" "app" {
  name               = "application-lb"
  load_balancer_type = "application"
  enable_deletion_protection = true  # Add this to satisfy the check
}

Or for a health check that expects a 200 response:

check "api_health" {
  data "http" "health" {
    url = "https://api.example.com/health"
  }

  assert {
    condition     = data.http.health.status_code == 200
    error_message = "API health check failed: status ${data.http.health.status_code}"
  }
}

Ensure your actual API is running and returns a 200 status code.

If your check block uses nested data sources to validate external endpoints or services, ensure those services are accessible and return expected values before running terraform apply.

# Test the health endpoint manually
curl -v https://api.example.com/health

# Verify DNS resolution
nslookup api.example.com

# Check network connectivity from your Terraform environment
terraform refresh  # Refresh data sources

Wait for the external service to be ready if it's being created by the same Terraform configuration, since check blocks run as the final step.

After fixing the underlying resource configuration, run terraform plan again to verify the assertion now passes, then apply the changes.

terraform plan
terraform apply

The check block will run as the last step. If the assertion still fails, the error will be displayed as a warning, but Terraform will continue. Review the warning and adjust the resource configuration further if needed.