allow overriding periodic jobs schedules

using a new config/periodic_jobs.yml file

test plan: edit config/periodic_jobs.yml, and verify that the overridden
jobs run at that new schedule. add an invalid override, and verify that
`script/delayed_job run` dies immediately.

closes #6875

Change-Id: Ia4611fb6f81fe82feda784300a3adf82e37a53e4
Reviewed-on: https://gerrit.instructure.com/8262
Tested-by: Hudson <hudson@instructure.com>
Reviewed-by: Cody Cutrer <cody@instructure.com>

config/periodic_jobs.yml.example

@@ -0,0 +1,15 @@
+# you can override the cron schedule for periodic jobs using this configuration file
+#
+# the default schedules are in config/periodic_jobs.rb
+#
+# shifting the time to a different hour is typically fine. changing the
+# frequency of the job is more dangerous -- make sure you understand the
+# consequences.
+
+development:
+  # the key is the name of the job, the value is the new cron line
+  # Reporting::CountsReport.process: "0 6 * * *"
+
+test:
+
+production:

vendor/plugins/delayed_job/lib/delayed/periodic.rb

@@ -1,5 +1,7 @@
 module Delayed
 class Periodic
+  attr_reader :name, :cron
+
   yaml_as "tag:ruby.yaml.org,2002:Delayed::Periodic"
 
   def to_yaml(opts = {})
@@ -13,6 +15,15 @@ class Periodic
   cattr_accessor :scheduled
   self.scheduled = {}
 
+  # throws an error if any cron override in config/periodic_jobs.yml is invalid
+  def self.audit_overrides!
+    overrides = Setting.from_config('periodic_jobs') || {}
+    overrides.each do |name, cron_line|
+      # throws error if the line is malformed
+      Rufus::CronLine.new(cron_line)
+    end
+  end
+
   def self.load_periodic_jobs_config
     require Rails.root+'config/periodic_jobs'
 
@@ -26,6 +37,8 @@ class Periodic
 
   def self.cron(job_name, cron_line, job_args = {}, &block)
     raise ArgumentError, "job #{job_name} already scheduled!" if self.scheduled[job_name]
+    override = (Setting.from_config('periodic_jobs') || {})[job_name]
+    cron_line = override if override
     self.scheduled[job_name] = self.new(job_name, cron_line, job_args, block)
   end
 

vendor/plugins/delayed_job/lib/delayed/pool.rb

@@ -70,8 +70,8 @@ class Pool
     say "Started job master", :info
     $0 = "delayed_jobs_pool"
     read_config(options[:config_file])
-    spawn_all_workers
     spawn_periodic_auditor
+    spawn_all_workers
     say "Workers spawned"
     join
     say "Shutting down"
@@ -126,6 +126,10 @@ class Pool
   def spawn_periodic_auditor
     return if @config[:disable_periodic_jobs]
 
+    # audit any periodic job overrides for invalid cron lines
+    # we do this here to fail as early as possible
+    Delayed::Periodic.audit_overrides!
+
     @periodic_thread = Thread.new do
       # schedule the initial audit immediately on startup
       schedule_periodic_audit

vendor/plugins/delayed_job/spec_canvas/shared_backend_spec.rb

@@ -430,6 +430,26 @@ shared_examples_for 'a backend' do
     it "should reject duplicate named jobs" do
       proc { Delayed::Periodic.cron('my SimpleJob', '*/15 * * * * *') {} }.should raise_error(ArgumentError)
     end
+
+    it "should allow overriding schedules using periodic_jobs.yml" do
+      Setting.set_config('periodic_jobs', { 'my ChangedJob' => '*/10 * * * * *' })
+      Delayed::Periodic.scheduled = {}
+      Delayed::Periodic.cron('my ChangedJob', '*/5 * * * * *') do
+        @backend.enqueue(SimpleJob.new)
+      end
+      Delayed::Periodic.scheduled['my ChangedJob'].cron.original.should == '*/10 * * * * *'
+      Delayed::Periodic.audit_overrides!
+    end
+
+    it "should fail if the override cron line is invalid" do
+      Setting.set_config('periodic_jobs', { 'my ChangedJob' => '*/10 * * * * * *' }) # extra asterisk
+      Delayed::Periodic.scheduled = {}
+      expect { Delayed::Periodic.cron('my ChangedJob', '*/5 * * * * *') do
+        @backend.enqueue(SimpleJob.new)
+      end }.to raise_error
+
+      expect { Delayed::Periodic.audit_overrides! }.to raise_error
+    end
   end
 
   module InDelayedJobTest