How to always run local-exec with Terraform

Sometimes there is a need to always run some terraform local-exec, so we can always execute a null_resource when doing an apply or applying it as a target.

So, how can you make sure to invalidate state for the null resource, so it always runs the local-exec script.

Using timestamp.

The following example always builds a docker image locally, when running both terraform apply generically to the *.tf file, or when targeting the resource directly.

resource "null_resource" "docker_build" {
  
  triggers = {
    always_run = "${timestamp()}"
  }

  provisioner "local-exec" {
    command = "docker build -t ${var.image_name}:${var.image_tag} ./path-to-docker-file-Folder"
    }
}

So now, whenever you run:

terraform apply

Or

terraform apply -target=null_resource.docker_build

The state will be invalid given the trigger block definition, with a variable that points to terraform’s timestamp method invocation that will invalidate previous state.

And that’s it.

Thank you for reading, hope it has been helpful.