Allow adopting hosts into inventory without provisioning (#10)

* Rework install logic slightly

* Support readonly mode for Terraform state

roles/infra/defaults/main.yml

@@ -1,6 +1,9 @@
 # The path to the Terraform binary, if not in the PATH
 terraform_binary_path:
 
+# If true, the state from the last deploy is used rather than provisioning
+terraform_readonly: false
+
 # By default, provision the infrastructure rather than tear it down
 terraform_state: present
 

roles/infra/tasks/inventory_adopt.yml

@@ -2,15 +2,15 @@
 
 - name: Set facts from Terraform outputs
   set_fact:
-    cluster_gateway_ip: "{{ terraform_provision.outputs.cluster_gateway_ip.value }}"
-    cluster_nodes: "{{ terraform_provision.outputs.cluster_nodes.value }}"
+    cluster_gateway_ip: "{{ terraform_provision_state.outputs.cluster_gateway_ip.value }}"
+    cluster_nodes: "{{ terraform_provision_state.outputs.cluster_nodes.value }}"
 
 # We allow the SSH private key file to be specified
 # If it is not, we expect a private key to be in the Terraform outputs
 - block:
     - name: Get SSH private key from Terraform output
       set_fact:
-        cluster_ssh_private_key: "{{ terraform_provision.outputs.cluster_ssh_private_key.value }}"
+        cluster_ssh_private_key: "{{ terraform_provision_state.outputs.cluster_ssh_private_key.value }}"
     - name: Get tempfile for SSH private key
       tempfile:
       register: cluster_ssh_private_key_tempfile

roles/infra/tasks/main.yml

@@ -1,23 +1,54 @@
 ---
 
-- name: Write backend configuration
+- name: Write backend type configuration
   copy:
     content: |
       terraform {
         backend "{{ terraform_backend_type }}" { }
       }
     dest: "{{ terraform_project_path }}/backend.tf"
 
+- name: Write backend configuration options
+  copy:
+    content: "{{ terraform_backend_config | to_json }}"
+    dest: "{{ terraform_project_path }}/backend_config.json"
+
 - name: Provision infrastructure using Terraform
   terraform:
     binary_path: "{{ terraform_binary_path or omit }}"
     project_path: "{{ terraform_project_path }}"
     state: "{{ terraform_state }}"
-    backend_config: "{{ terraform_backend_config }}"
+    backend_config_files:
+      - "{{ terraform_project_path }}/backend_config.json"
     force_init: yes
     init_reconfigure: yes
     variables: "{{ terraform_variables }}"
-  register: terraform_provision
+  register: terraform_provision_state
+  when: not terraform_readonly
+
+- name: Get outputs from Terraform state
+  block:
+    - name: Initialise Terraform
+      command: >-
+        {{ terraform_binary_path | default('terraform', True) }}
+          -chdir="{{ terraform_project_path }}"
+          init
+          -input=false
+          -reconfigure
+          -backend-config="{{ terraform_project_path }}/backend_config.json"
+
+    - name: Pull Terraform state
+      command: >-
+        {{ terraform_binary_path | default('terraform', True) }}
+          -chdir="{{ terraform_project_path }}"
+          state
+          pull
+      register: terraform_state_pull
+
+    - name: Set Terraform provision state fact
+      set_fact:
+        terraform_provision_state: "{{ terraform_state_pull.stdout | from_json }}"
+  when: terraform_readonly
 
 - name: Populate in-memory inventory
   include_tasks: inventory_adopt.yml

roles/install/defaults/main.yml

@@ -13,8 +13,13 @@ terraform_zip_name: terraform_{{ terraform_version_max }}_{{ terraform_os }}_{{
 # The URL of the Terraform binary
 terraform_binary_url: https://releases.hashicorp.com/terraform/{{ terraform_version_max }}/{{ terraform_zip_name }}
 
-# The directory to put the Terraform binary in
+# The directory to put the Terraform binary in if we download it
 terraform_binary_directory: /usr/local/bin
 
+# List of directories to search for a suitable Terraform
+# By default, search the binary directory + the directories in the path
+terraform_additional_search_directories: "{{ lookup('ansible.builtin.env', 'PATH') | split(':') | list }}"
+terraform_search_directories: "{{ ([terraform_binary_directory] + terraform_additional_search_directories) | unique }}"
+
 # Become root when downloading Terraform binary
 terraform_download_binary_become: false

roles/install/tasks/main.yml

@@ -1,88 +1,66 @@
 ---
 
-- name: Get directories on the PATH
-  set_fact:
-    terraform_path_dirs: "{{ terraform_path_dirs | default([]) + [item] }}"
-  loop: "{{ lookup('ansible.builtin.env', 'PATH') | split(':') }}"
-
-- name: Check if Terraform binary exists in PATH directories
+- name: Check if Terraform binary exists in search directories
   stat:
     path: "{{ item }}/terraform"
   register: terraform_binary_paths
-  loop: "{{ ( [terraform_binary_directory] + terraform_path_dirs ) | unique }}"
+  loop: "{{ terraform_search_directories }}"
 
-- name: Check Terraform versions available on the PATH
-  command:
-    cmd: "{{ item.stat.path }} version -json"
-  register: current_terraform_version
+- name: Get available Terraform versions
+  command: "{{ item.stat.path }} version -json"
+  register: terraform_version_info
   changed_when: false
-  loop: "{{ terraform_binary_paths.results | selectattr('stat.exists', 'equalto', True) }}"
+  loop: "{{ terraform_binary_paths.results | selectattr('stat.exists') }}"
   loop_control:
     label: "{{ item.stat.path }}"
 
-- name: Set current Terraform versions fact
+- name: Set Terraform versions fact
   set_fact:
-    terraform_version_stdout: >-
-      {{
-        terraform_version_stdout | default([]) + 
-          [
-            {'path': item.item.stat.path, 'version': item.stdout | from_json }
-            ] 
-        }}
-  loop: "{{ current_terraform_version.results }}"
-  loop_control:
-    label: "{{ item.item.stat.path }}"
+    terraform_available_versions: >-
+      [
+        {% for item in terraform_version_info.results %}
+        ("{{ item.item.stat.path }}", "{{ item.stdout | from_json | json_query('terraform_version') }}"),
+        {% endfor %}
+      ]
 
-- name: Filter Terraform paths to match version requirements
+- name: Filter Terraform versions
   set_fact:
-    terraform_filtered_path: >-
-      {{
-        terraform_version_stdout | 
-        sort(attribute='version.terraform_version') |
-        selectattr(
-          'version.terraform_version', 'version', terraform_version_min, '>='
-          ) |
-        selectattr(
-          'version.terraform_version', 'version', terraform_version_max, '<='
-          ) |
-        last | 
-        default([])
+    terraform_acceptable_versions: >-
+      {{-
+        terraform_available_versions |
+          selectattr('1', 'version', terraform_version_min, '>=') |
+          selectattr('1', 'version', terraform_version_max, '<=') |
+          sort(attribute = '1', reverse = True)
       }}
 
-- name: Set current Terraform path fact
+- name: Set Terraform binary path
   set_fact:
-    terraform_binary_path: "{{ terraform_filtered_path.path }}"
-  when:
-    - terraform_filtered_path | length == 1
+    terraform_binary_path: "{{ terraform_acceptable_versions.0.0 }}"
+    terraform_detected_version: "{{ terraform_acceptable_versions.0.1 }}"
+  when: "terraform_acceptable_versions | length > 0"
 
 - name: Download Terraform binary if an acceptable version is not available
   block:
-  - name: Ensure Terraform bin directory exists
-    file:
-      path: "{{ terraform_binary_directory }}"
-      state: directory
+    - name: Ensure Terraform bin directory exists
+      file:
+        path: "{{ terraform_binary_directory }}"
+        state: directory
 
-  - name: Download Terraform binary
-    unarchive:
-      remote_src: yes
-      src: "{{ terraform_binary_url }}"
-      dest: "{{ terraform_binary_directory }}"
-
-  - name: Set current Terraform path fact
-    set_fact:
-      terraform_binary_path: "{{ terraform_binary_directory }}/terraform"
-
+    - name: Download Terraform binary
+      unarchive:
+        remote_src: yes
+        src: "{{ terraform_binary_url }}"
+        dest: "{{ terraform_binary_directory }}"
+
+    - name: Set current Terraform path fact
+      set_fact:
+        terraform_binary_path: "{{ terraform_binary_directory }}/terraform"
   when: terraform_binary_path is not defined
   become: "{{ terraform_download_binary_become }}"
 
 - name: Display Terraform path and version message
   debug:
     msg: >- 
-      Using Terraform version {{ terraform_detected_version }}
+      Using Terraform version
+      {{ terraform_detected_version | default(terraform_version_max) }}
       from {{ terraform_binary_path }}.
-  vars:
-    terraform_detected_version: >-
-      {{ terraform_filtered_path.version.terraform_version
-        if terraform_filtered_path | length > 0
-        else terraform_version_max
-      }}