Fix E2BIG, use tempfile instead of env var for loaded config file list

lib/sensu/settings/loader.rb

@@ -1,5 +1,6 @@
 require "sensu/settings/validator"
 require "multi_json"
+require "tempfile"
 
 module Sensu
   module Settings
@@ -135,11 +136,26 @@ def load_directory(directory)
         end
       end
 
+      # Create a temporary file containing the colon delimited list of
+      # loaded configuration files.
+      #
+      # @return [String] tempfile path.
+      def create_loaded_tempfile!
+        file = Tempfile.new("sensu_loaded_files")
+        file.write(@loaded_files.join(":"))
+        file.close
+        file.path
+      end
+
       # Set Sensu settings related environment variables. This method
-      # currently sets SENSU_CONFIG_FILES, a colon delimited list of
-      # loaded config files.
+      # sets `SENSU_LOADED_TEMPFILE` to a new temporary file path,
+      # a file containing the colon delimited list of loaded
+      # configuration files (using `create_loaded_tempfile!()`. The
+      # environment variable `SENSU_CONFIG_FILES` has been removed,
+      # due to the exec ARG_MAX (E2BIG) error when spawning processes
+      # after loading many configuration files (e.g. > 2000).
       def set_env!
-        ENV["SENSU_CONFIG_FILES"] = @loaded_files.join(":")
+        ENV["SENSU_LOADED_TEMPFILE"] = create_loaded_tempfile!
       end
 
       # Validate the loaded settings.

spec/loader_spec.rb

@@ -130,7 +130,9 @@
     @loader.load_directory(@config_dir)
     expect(@loader.loaded_files.size).to eq(3)
     @loader.set_env!
-    expect(ENV["SENSU_CONFIG_FILES"].split(":")).to eq(@loader.loaded_files)
+    expect(ENV["SENSU_LOADED_TEMPFILE"]).to match(/sensu_loaded_files/)
+    loaded_files = IO.read(ENV["SENSU_LOADED_TEMPFILE"])
+    expect(loaded_files.split(":")).to eq(@loader.loaded_files)
   end
 
   it "can load settings and determine if certain definitions exist" do

spec/settings_spec.rb

@@ -38,7 +38,9 @@
     expect(settings[:checks][:merger][:command]).to eq("echo -n merger")
     expect(settings[:checks][:merger][:subscribers]).to eq(["foo", "bar"])
     expect(settings[:checks][:nested][:command]).to eq("true")
-    expect(ENV["SENSU_CONFIG_FILES"].split(":")).to eq(settings.loaded_files)
+    expect(ENV["SENSU_LOADED_TEMPFILE"]).to match(/sensu_loaded_files/)
+    loaded_files = IO.read(ENV["SENSU_LOADED_TEMPFILE"])
+    expect(loaded_files.split(":")).to eq(settings.loaded_files)
     ENV["RABBITMQ_URL"] = nil
   end