Critical Plugins (#1064)

This adds a new Ohai configuration `critical_plugins` which will cause
Ohai to exit (or `fail` if inside of Chef) if the plugins in the list do
not run successfully.

This feature only supports Ohai 7-style named plugins, not the ancient
Ohai 6-style stuff.

Tests to follow, but:

```
$ cat /home/phild/ohai.rb
ohai.critical_plugins << :Filesystem
$ ./bin/ohai -c /home/phild/ohai.rb
[2017-10-03T13:43:14-07:00] INFO: The plugin path /etc/chef/ohai/plugins does not exist. Skipping...
[2017-10-03T13:43:14-07:00] ERROR: The following plugins marked as critical failed: [:Filesystem]
```

And when I run Chef:
```
[2017-10-03T13:44:11-07:00] FATAL: RuntimeError: The following plugins marked as critical failed: [:Filesystem2]. Failing Chef run.
```

This fixes #879.

Signed-off-by: Phil Dibowitz <phil@ipom.com>

7 files changed, 58 insertions, 0 deletions

diff --git a/RELEASE_NOTES.md b/RELEASE_NOTES.md
index 657a2911..5f53e49e 100644
--- a/RELEASE_NOTES.md
+++ b/RELEASE_NOTES.md
@@ -1,3 +1,13 @@
+# Unreleased
+
+### Critical Plugins
+
+Users can now specify a list of plugins which are `critical`. Critical plugins will cause Ohai to fail if they do not run successfully (and thus cause a Chef run using Ohai to fail). The syntax for this is:
+
+```
+ohai.critical_plugins << :Filesystem
+```
+
 # Ohai Release Notes 13.5
 
 ### Correctly detect IPv6 routes ending in ::
diff --git a/lib/ohai/config.rb b/lib/ohai/config.rb
index 0f90f944..aa73900b 100644
--- a/lib/ohai/config.rb
+++ b/lib/ohai/config.rb
@@ -35,6 +35,7 @@ module Ohai
       default :log_location, STDERR
       default :plugin, Ohai::PluginConfig.new { |h, k| h[k] = Ohai::PluginConfig.new }
       default :plugin_path, [ File.expand_path(File.join(File.dirname(__FILE__), "plugins")), ChefConfig::Config.platform_specific_path("/etc/chef/ohai/plugins") ]
+      default :critical_plugins, []
     end
   end
 
diff --git a/lib/ohai/dsl/plugin.rb b/lib/ohai/dsl/plugin.rb
index e3694ac1..f187aeaf 100644
--- a/lib/ohai/dsl/plugin.rb
+++ b/lib/ohai/dsl/plugin.rb
@@ -85,10 +85,12 @@ module Ohai
       include Ohai::Util::FileHelper
 
       attr_reader :data
+      attr_reader :failed
 
       def initialize(data)
         @data = data
         @has_run = false
+        @failed = false
       end
 
       def run
@@ -182,8 +184,10 @@ module Ohai
       def safe_run
         run
       rescue Ohai::Exceptions::Error => e
+        @failed = true
         raise e
       rescue => e
+        @failed = true
         Ohai::Log.debug("Plugin #{name} threw #{e.inspect}")
         e.backtrace.each { |line| Ohai::Log.debug( line ) }
       end
diff --git a/lib/ohai/exception.rb b/lib/ohai/exception.rb
index 5db9c597..0cae0995 100644
--- a/lib/ohai/exception.rb
+++ b/lib/ohai/exception.rb
@@ -29,5 +29,6 @@ module Ohai
     class DependencyNotFound < Error; end
     class AttributeSyntaxError < Error; end
     class PluginConfigError < Error; end
+    class CriticalPluginFailure < Error; end
   end
 end
diff --git a/lib/ohai/runner.rb b/lib/ohai/runner.rb
index 6368cbe3..05fd7cfc 100644
--- a/lib/ohai/runner.rb
+++ b/lib/ohai/runner.rb
@@ -23,11 +23,13 @@ require "benchmark"
 module Ohai
   class Runner
 
+    attr_reader :failed_plugins
     # safe_run: set to true if this runner will run plugins in
     # safe-mode. default false.
     def initialize(controller, safe_run = false)
       @provides_map = controller.provides_map
       @safe_run = safe_run
+      @failed_plugins = []
     end
 
     # Runs plugins and any un-run dependencies.
@@ -86,6 +88,9 @@ module Ohai
 
         if dependency_providers.empty?
           @safe_run ? next_plugin.safe_run : next_plugin.run
+          if next_plugin.failed
+            @failed_plugins << next_plugin.name
+          end
         else
           visited << next_plugin << dependency_providers.first
         end
diff --git a/lib/ohai/system.rb b/lib/ohai/system.rb
index 1002e198..dafa90bc 100644
--- a/lib/ohai/system.rb
+++ b/lib/ohai/system.rb
@@ -47,6 +47,7 @@ module Ohai
       @cli = config[:invoked_from_cli]
       @plugin_path = ""
       @config = config
+      @failed_plugins = []
       reset_system
     end
 
@@ -107,6 +108,16 @@ module Ohai
         Ohai::Log.error("Encountered error while running plugins: #{e.inspect}")
         raise
       end
+      critical_failed = Ohai::Config.ohai[:critical_plugins] & @runner.failed_plugins
+      unless critical_failed.empty?
+        msg = "The following Ohai plugins marked as critical failed: #{critical_failed}"
+        if @cli
+          Ohai::Log.error(msg)
+          exit(true)
+        else
+          raise Ohai::Exceptions::CriticalPluginFailure, "#{msg}. Failing Chef run."
+        end
+      end
 
       # Freeze all strings.
       freeze_strings!
diff --git a/spec/unit/system_spec.rb b/spec/unit/system_spec.rb
index b212ea0b..a2e85843 100644
--- a/spec/unit/system_spec.rb
+++ b/spec/unit/system_spec.rb
@@ -43,6 +43,7 @@ describe "Ohai::System" do
       config = {
         disabled_plugins: [ :Foo, :Baz ],
         directory: "/some/extra/plugins",
+        critical_plugins: [ :Foo, :Bar ],
       }
       Ohai::System.new(config)
       config.each do |option, value|
@@ -309,6 +310,15 @@ Ohai.plugin(:Park) do
 end
 EOF
 
+      with_plugin("fails.rb", <<EOF)
+Ohai.plugin(:Fails) do
+  provides 'fails'
+  collect_data(:default) do
+    fail 'thing'
+  end
+end
+EOF
+
       it "should collect data from all the plugins" do
         Ohai.config[:plugin_path] = [ path_to(".") ]
         ohai.all_plugins
@@ -343,6 +353,22 @@ EOF
           expect(ohai.data[:park]).to eq("plants")
         end
       end
+
+      describe "when using :critical_plugins" do
+        before do
+          Ohai.config[:critical_plugins] = [ :Fails ]
+        end
+        after do
+          Ohai.config[:critical_plugins] = []
+        end
+
+        it "should fail when critical plugins fail" do
+          Ohai.config[:plugin_path] = [ path_to(".") ]
+          expect(Ohai::Log).to receive(:error).with(/marked as critical/)
+          ohai.all_plugins
+        end
+
+      end
     end
 
     when_plugins_directory "contains v6 & v7 plugins in different directories" do