feature: allow downloading of package by remote host

Currently node_exporter install always downloads the package on the
localhost and unpacks it there then uploads it to the remote host.

In the case the ansible controller is at the other end of a thin
network pipe, or if it may not even have access to the package URL,
it may be desirable to download and unpack it on the remote host
instead.

This change adds that ability as an optional behavior to _common/install
and wires it up for use by node_exporter, using the
node_exporter_localhost_download variable. The default for node exporter
and any other binaries remains the same as before: delegate to
localhost.

Fixes prometheus-community#389.

roles/_common/tasks/install.yml

@@ -46,12 +46,12 @@
     - install
     - "{{ ansible_parent_role_names | first | regex_replace(ansible_collection_name ~ '.', '') }}_install"
 
-- name: "Create localhost binary cache path"
+- name: "Create binary cache path on {{ 'localhost' if (_common_delegate_to_localhost | bool) else 'remote host'}}"
   ansible.builtin.file:
     path: "{{ _common_local_cache_path }}"
     state: directory
     mode: 0755
-  delegate_to: localhost
+  delegate_to: "{{ 'localhost' if (_common_delegate_to_localhost | bool) else omit }}"
   check_mode: false
   become: false
   tags:
@@ -78,7 +78,7 @@
       run_once: true
       when: (_common_checksums_url)
 
-    - name: "Download {{ __common_binary_basename }}"
+    - name: "Download {{ __common_binary_basename }} from {{ _common_binary_url }} on {{ 'localhost' if (_common_delegate_to_localhost | bool) else 'remote host'}}"
       ansible.builtin.get_url:
         url: "{{ _common_binary_url }}"
         dest: "{{ _common_local_cache_path }}/{{ _common_binary_name | default(__common_binary_basename) }}"
@@ -90,17 +90,18 @@
       retries: 5
       delay: 2
       # run_once: true  # <-- this can't be set due to multi-arch support
-      delegate_to: localhost
+      delegate_to: "{{ 'localhost' if (_common_delegate_to_localhost | bool) else omit }}"
       check_mode: false
 
-    - name: "Unpack binary archive {{ __common_binary_basename }}"
+    - name: "Unpack binary archive {{ __common_binary_basename }} on {{ 'localhost' if (_common_delegate_to_localhost | bool) else 'remote host'}}"
       ansible.builtin.unarchive:
         src: "{{ _common_local_cache_path }}/{{ __common_binary_basename }}"
         dest: "{{ _common_local_cache_path }}"
         mode: 0755
         list_files: true
         extra_opts: "{{ _common_binary_unarchive_opts | default(omit, true) }}"
-      delegate_to: localhost
+        remote_src: "{{ not (_common_delegate_to_localhost | bool) }}"
+      delegate_to: "{{ 'localhost' if (_common_delegate_to_localhost | bool) else omit }}"
       check_mode: false
       when: __common_binary_basename is search('\.zip$|\.tar\.gz$')
 
@@ -129,6 +130,7 @@
     mode: 0755
     owner: root
     group: root
+    remote_src: "{{ not (_common_delegate_to_localhost | bool) }}"
   loop: "{{ _common_binaries }}"
   become: true
   notify:

roles/_common/vars/main.yml

@@ -19,6 +19,7 @@ _common_tls_server_config: {}
 _common_http_server_config: {}
 _common_basic_auth_users: {}
 _common_web_listen_address: ""
+_common_delegate_to_localhost: "true"
 # Variables that should not be overwritten
 __common_binary_basename: "{{ _common_binary_url | urlsplit('path') | basename }}"
 __common_github_api_headers: "{{ {'GITHUB_TOKEN': lookup('ansible.builtin.env', 'GITHUB_TOKEN')} if (lookup('ansible.builtin.env', 'GITHUB_TOKEN')) else {} }}"

roles/node_exporter/defaults/main.yml

@@ -33,3 +33,8 @@ node_exporter_system_user: "{{ node_exporter_system_group }}"
 node_exporter_config_dir: "/etc/node_exporter"
 # Local path to stash the archive and its extraction
 node_exporter_local_cache_path: "/tmp/node_exporter-{{ ansible_system | lower }}-{{ _node_exporter_go_ansible_arch }}/{{ node_exporter_version }}"
+# If true (the default) we download node exporter archive and unpack it on localhost, before
+# uploading it to the remote host(s). If false we download and unpack the archive on the remote
+# host directly, which may be useful if the ansible controller host is slower (network-wise)
+# than the remote host.
+node_exporter_localhost_download: true

roles/node_exporter/meta/argument_specs.yml

@@ -82,3 +82,6 @@ argument_specs:
       node_exporter_config_dir:
         description: "Path to directory with node_exporter configuration"
         default: "/etc/node_exporter"
+      node_exporter_localhost_download:
+        description: "Determines if the node exporter package archive is downloaded and extracted on local (true) or remote host (false)"
+        default: true

roles/node_exporter/tasks/main.yml

@@ -21,6 +21,7 @@
     _common_system_user: "{{ node_exporter_system_user }}"
     _common_config_dir: "{{ node_exporter_config_dir }}"
     _common_binary_unarchive_opts: ['--strip-components=1']
+    _common_delegate_to_localhost: "{{ node_exporter_localhost_download }}"
   tags:
     - node_exporter_install