This data source puts rendered template parts together for generating cloud-init user-data.

nmg-jenkins-terraform-cloud-init-template.tf

data "template_cloudinit_config" "agent_init" {
  gzip          = false
  base64_encode = false

  part {
    filename     = "agent.cfg"
    content_type = "text/cloud-config"
    content      = "${data.template_file.agent_write_files.rendered}"
  }

  part {
    content_type = "text/cloud-config"
    content      = "${data.template_file.agent_runcmd.rendered}"
  }

  part {
    content_type = "text/cloud-config"
    content      = "${var.extra_agent_userdata}"
    merge_type   = "${var.extra_agent_userdata_merge}"
  }

  part {
    content_type = "text/cloud-config"
    content      = "${data.template_file.agent_end.rendered}"
    merge_type   = "list(append)+dict(recurse_array)+str()"
  }
}