Made sense of terraform's cloud-init temmplate example with docker installation

terraform/multi-part cloud-init/data.tf

@@ -12,12 +12,17 @@ data "cloudinit_config" "azurerm_linux_virtual_machine" {
     filename     = "base"
   }
 
-  # part {
-  #   content      = file("${path.module}/templates/n-th.yaml")
-  #   content_type = "text/cloud-config"
-  #   merge_type   = "dict(recurse_array,no_replace)+list(append)"
-  #   filename     = "n-th.yaml"
-  # }
+  part {
+    content = templatefile(
+      "${path.module}/templates/docker-ce.yaml.tftpl",
+      {
+        user = "azureuser"
+      }
+    )
+    content_type = "text/cloud-config"
+    merge_type   = "dict(recurse_array,no_replace)+list(append)"
+    filename     = "docker"
+  }
 }
 
 data "cloudinit_config" "oci_core_instance" {
@@ -33,13 +38,13 @@ data "cloudinit_config" "oci_core_instance" {
 
   part {
     content = templatefile(
-      "${path.module}/templates/boinc-client.oci-core-instance.yaml.tftpl",
+      "${path.module}/templates/docker-ce.yaml.tftpl",
       {
         user = "opc"
       }
     )
     content_type = "text/cloud-config"
     merge_type   = "dict(recurse_array,no_replace)+list(append)"
-    filename     = "n-th.yaml"
+    filename     = "docker"
   }
 }

terraform/multi-part cloud-init/templates/boinc-client.oci-core-instance.yaml.tftpl

@@ -1,6 +0,0 @@
-#cloud-config
-
-packages:
-  - boinc-client
-
-# Something about user ${user}

terraform/multi-part cloud-init/templates/docker-ce.yaml.tftpl

@@ -0,0 +1,20 @@
+#cloud-config
+
+packages:
+  - docker-ce
+
+runcmd:
+
+  # Give the user permissions to use Docker without `sudo`ing.
+  # The 'users' module overrode *both* the SSH keys *and* group assignments in
+  # previous tests. (┛◉Д◉)┛彡┻━┻
+  - grep -qE '^docker:' /etc/group && usermod -a -G docker ${user} || true
+
+yum_repos:
+  docker-ce:
+    name: Docker CE Stable - $basearch
+    enabled: true
+    baseurl: https://download.docker.com/linux/rhel/$releasever/$basearch/stable
+    priority: 1
+    gpgcheck: true
+    gpgkey: https://download.docker.com/linux/rhel/gpg