Zip AWS Lambda Function on the Fly

Terraform has been a great tool for me to maintain infrastructure as a code (IaC). In fact, 90% of our current environment infrastructure is provisioned via Terraform.

Lately, I've stumbled upon a challenging case: How to zip AWS Lambda function on the fly without using external script?

Well, apparently there's a little trick that does this job: archive_file data source:

data "archive_file" "lambda_zip" {
    type        = "zip"
    source_dir  = "source"
    output_path = "lambda.zip"
}

resource "aws_lambda_function" "func" {
  filename         = "lambda.zip"
  source_code_hash = "${data.archive_file.lambda_zip.output_base64sha256}"
  function_name    = "my_lambda"
  role             = "${aws_iam_role.lambda.arn}"
  description      = "Function desc"
  handler          = "index.handler"
  runtime          = "nodejs4.3"
}

The archive_file data source generates a zip archive from the contents of the source directory. Terraform then uses the output_base64sha256 attribute to detect changes in the source code -- if any file in the source directory changes, Terraform will automatically re-zip and update the Lambda function.

This approach has several advantages:

• No external scripts needed -- everything stays within Terraform's declarative configuration.
• Automatic change detection -- the source_code_hash ensures Lambda is updated whenever the source code changes.
• Simple and clean -- just two resource blocks and you're done.

The archive_file data source supports multiple modes:

• source_dir -- zip an entire directory
• source_file -- zip a single file
• source_content and source_content_filename -- create a zip from inline content

This is particularly useful in CI/CD pipelines where you want Terraform to handle the entire deployment lifecycle, including packaging the Lambda function code, without relying on separate build steps or shell scripts.