fb_systemd: make knob for mgmt of default target

Summary:

Make knob for mgmt of default target, so that it's possible to opt out as needed

Differential Revision: D51510688

fbshipit-source-id: 7c1a0f44975b4aa49ebba0ff5d81700297412e87

cookbooks/fb_systemd/README.md

@@ -34,6 +34,7 @@ Attributes
 * node['fb_systemd']['tmpfiles_excluded_prefixes']
 * node['fb_systemd']['preset']
 * node['fb_systemd']['manage_systemd_packages']
+* node['fb_systemd']['manage_default_target']
 * node['fb_systemd']['boot']['enable']
 * node['fb_systemd']['boot']['path']
 * node['fb_systemd']['boot']['loader']
@@ -408,6 +409,11 @@ By default this cookbook keeps the systemd packages up-to-date, but if you
 want to manage them locally, simply set
 `node['fb_systemd']['manage_systemd_packages']` to false.
 
+### Default target
+By default this cookbook manages the default systemd target, but if you
+want otherwise, set
+`node['fb_systemd']['manage_default_target']` to false.
+
 ### Boot
 You can choose whether or not to enable `systemd-boot` with the
 `node['fb_systemd']['boot']['enable']` attribute, which defaults to `false`.

cookbooks/fb_systemd/attributes/default.rb

@@ -131,6 +131,7 @@
   'tmpfiles_excluded_prefixes' => [],
   'preset' => {},
   'manage_systemd_packages' => true,
+  'manage_default_target' => true,
   'boot' => {
     'enable' => false,
     'path' => esp_path,

cookbooks/fb_systemd/recipes/default.rb

@@ -153,12 +153,14 @@
 end
 
 directory '/etc/systemd/user/default.target.wants' do
+  only_if { node['fb_systemd']['manage_default_target'] }
   owner 'root'
   group 'root'
   mode '0755'
 end
 
 execute 'set default target' do
+  only_if { node['fb_systemd']['manage_default_target'] }
   only_if do
     current = shell_out('systemctl get-default').stdout.strip
     is_ignored = node['fb_systemd']['ignore_targets'].include?(current)
@@ -173,6 +175,7 @@
 end
 
 link '/etc/systemd/system/default.target' do
+  only_if { node['fb_systemd']['manage_default_target'] }
   only_if do
     FB::Version.new(node['packages']['systemd'][
       'version']) < FB::Version.new('205')

cookbooks/fb_systemd/spec/default_spec.rb

@@ -49,4 +49,16 @@
       tc.fixture('system.conf'),
     )
   end
+
+  it 'should skip default target when manage_default_target is false' do
+    chef_run.converge(described_recipe) do |node|
+      node.default['fb_systemd']['manage_default_target'] = false
+    end
+    expect(chef_run).not_to run_execute('set default target')
+  end
+
+  it 'should set default target when manage_default_target is true' do
+    chef_run.converge(described_recipe)
+    expect(chef_run).not_to run_execute('set default target')
+  end
 end