fb_grafana: Add support for immutable plugins (facebook#336)

Summary:
Grafana has started shipping with certain core functionality as a
"plugin". The plugin is extracted into the same directory as
user-controlled plugins, and the CLI does not differentiate, but
attempting to remove or upgrade them throws an error.

This PR adds support for handling those more sanely.

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

Pull Request resolved: facebook#336

Differential Revision: D79735298

fbshipit-source-id: 2e338a84acf77a774ba04940c2158755d47cf035

Author: jaymzh

cookbooks/fb_grafana/README.md

@@ -13,6 +13,8 @@ Attributes
 * node['fb_grafana']['gen_selfsigned_cert']
 * node['fb_grafana']['plugins']
 * node['fb_grafana']['plugins'][$PLUGIN]
+* node['fb_grafana']['immutable_plugins']
+* node['fb_grafana']['immutable_plugins'][$PLUGIN]
 * node['fb_grafana']['datasources']
 * node['fb_grafana']['datasources'][$NAME]
 * node['fb_grafana']['datasources'][$NAME][$CONFIG]
@@ -57,6 +59,20 @@ version will be pinned.
 Note that we ensure these are managed idempotently, a plugin is never touched if
 it's on the desired version.
 
+Note that some plugins are considered "immutable" - they are part of the
+distribution of Grafana itself. Since they get extracted into the same plugins
+directory, there is no programatic way to tell them apart. As such we keep an
+`immutable_plugins` hash that's the same structure as the `plugins` hash. Plugins
+in this list (which we attempt to keep up-to-date in `attributes/default.rb`, but
+you may add to if your distribution has different immutable plugins), will not be
+removed by this cookbook, even if they are not in the `plugins` list. Note that
+the _value_ is ignored, and thus should be set to `nil` for consistency. It is
+a hash instead of an array for easy modification.
+
+If an immutable plugin appears in `plugins` at a specific version, a warning
+will be displayed saying that the plugin cannot be directly managed, and then
+that plugin will be ignored.
+
 ### Data Sources
 You can populate datasources by adding them to the hash
 `node['fb_grafana']['datasources']`. Note that this uses the Provisioning

cookbooks/fb_grafana/attributes/default.rb

@@ -12,6 +12,12 @@
   },
   'gen_selfsigned_cert' => false,
   'plugins' => {},
+  'immutable_plugins' => {
+    'grafana-exploretraces-app' => nil,
+    'grafana-lokiexplore-app' => nil,
+    'grafana-metricsdrilldown-app' => nil,
+    'grafana-pyroscope-app' => nil,
+  },
   'datasources' => {},
   'version' => nil,
 }

cookbooks/fb_grafana/resources/plugins.rb

@@ -11,6 +11,15 @@
     '/var/lib/grafana/plugins'
   basecmd = "grafana-cli --pluginsDir #{plugin_dir}"
   node['fb_grafana']['plugins'].each do |plugin, version|
+    if node['fb_grafana']['immutable_plugins'].key?(plugin) && !version.nil?
+      Chef::Log.warn(
+        "fb_grafana: Plugin #{plugin} is configured to be installed at " +
+        "version #{version}, but #{plugin} is a built-in/immutable plugin " +
+        'that cannot be managed by the user.',
+      )
+      next
+    end
+
     # If a version is specified, see if it's installed and on that version...
     if version && installed[plugin] == version
       Chef::Log.debug(
@@ -50,7 +59,8 @@
     # NOTE WELL: Cannot use ruby-style
     #    if node['fb_grafana']['plugins'][plugin]
     # because the value can be nil, which evaluates to false!
-    next if node['fb_grafana']['plugins'].include?(plugin)
+    next if node['fb_grafana']['plugins'].key?(plugin)
+    next if node['fb_grafana']['immutable_plugins'].key?(plugin)
 
     execute "Uninstall grafana plugin #{plugin}" do
       command "#{basecmd} plugins uninstall #{plugin}"