Allow skipping tenants when running patches

docs/usage.md

@@ -63,6 +63,24 @@ end
 *Note:* Make sure your sidekiq queue is able to process concurrent jobs.
 You can use ```config.sidekiq_options``` to customise it.
 
+### Skipping tenants when running patches for multiple tenants
+
+If you are using the Apartment gem, the patches will run across all tenants by default. If you wish to only run patches against a subset of tenants, you can use the `ONLY_TENANTS` env var, like so
+
+```bash
+# This will only run for my_tenant and other_tenant, provided they are listed as tenants by the Apartment gem
+ONLY_TENANTS=my_tenant,other_tenant bundle exec rake patches:run
+```
+
+Similarly if you want to run patches against all tenants _except_ for a select few, you can use the `SKIP_TENANTS` env var, like so
+
+```bash
+# This will run for all tenants EXCEPT my_tenant and other_tenant
+SKIP_TENANTS=my_tenant,other_tenant bundle exec rake patches:run
+```
+
+If you specify both env vars, the `ONLY_TENANTS` env var will take precedence
+
 ### Application version verification
 
 In environments where a rolling update of sidekiq workers is performed during the deployment, multiple versions of the application run at the same time. If a Patches job is scheduled by the new application version during the rolling update, there is a possibility that it can be executed by the old application version, which will not have all the required patch files.

lib/patches.rb

@@ -31,3 +31,4 @@ def self.logger=(log)
 require "patches/tenant_runner"
 require "patches/notifier"
 require "patches/worker" if defined?(Sidekiq)
+require "patches/tenant_finder"

lib/patches/tenant_finder.rb

@@ -0,0 +1,28 @@
+class Patches::TenantFinder
+
+  def tenant_names
+    @tenant_names ||= begin
+      if only_tenant_names.any?
+        apartment_tenant_names.select { |tenant_name| only_tenant_names.include?(tenant_name) }
+      elsif skip_tenant_names.any?
+        apartment_tenant_names.reject { |tenant_name| skip_tenant_names.include?(tenant_name) }
+      else
+        apartment_tenant_names
+      end
+    end
+  end
+
+  private
+
+  def apartment_tenant_names
+    Apartment.tenant_names || []
+  end
+
+  def only_tenant_names
+    ENV['ONLY_TENANTS'] ? ENV['ONLY_TENANTS'].split(',').map { |s| s.strip } : []
+  end
+
+  def skip_tenant_names
+    ENV['SKIP_TENANTS'] ? ENV['SKIP_TENANTS'].split(',').map { |s| s.strip } : []
+  end
+end

lib/patches/tenant_runner.rb

@@ -2,9 +2,8 @@ class Patches::TenantRunner
   include Patches::TenantRunConcern
   attr_accessor :path
 
-  def initialize(path: nil, tenants: nil)
+  def initialize(path: nil)
     @path = path
-    @tenants = tenants
   end
 
   def perform
@@ -23,7 +22,7 @@ def perform
   end
 
   def tenants
-    @tenants ||= (Apartment.tenant_names || [])
+    @tenants ||= Patches::TenantFinder.new.tenant_names
   end
 
   private

lib/tasks/patches.rake

@@ -17,10 +17,6 @@ namespace :patches do
     end
   end
 
-  def tenants
-    ENV['DB'] ? ENV['DB'].split(',').map { |s| s.strip } : Apartment.tenant_names || []
-  end
-
   task :pending => [:environment] do
     Patches::Pending.new.each do |patch|
       puts patch

spec/tenant_finder_spec.rb

@@ -0,0 +1,49 @@
+require 'spec_helper'
+require 'patches/tenant_finder'
+
+describe Patches::TenantFinder do
+  describe '#tenant_names' do
+    subject { tenant_finder.tenant_names }
+    let(:tenant_finder) { Patches::TenantFinder.new }
+    let(:apartment_tenant_names) { ['test1', 'test2', 'test3'] }
+    let(:only_tenants_env_var) { nil }
+    let(:skip_tenants_env_var) { nil }
+
+    before do
+      allow(Apartment).to receive(:tenant_names).and_return(apartment_tenant_names)
+      allow(ENV).to receive(:[]).with('ONLY_TENANTS').and_return(only_tenants_env_var)
+      allow(ENV).to receive(:[]).with('SKIP_TENANTS').and_return(skip_tenants_env_var)
+    end
+
+    context 'when no env vars are set' do
+      it 'returns the list from Apartment' do
+        expect(subject).to match_array(['test1', 'test2', 'test3'])
+      end
+    end
+
+    context 'when ONLY_TENANTS is set' do
+      let(:only_tenants_env_var) { 'test1,test2' }
+
+      it 'returns a subset of the Apartment list filtered by the env var' do
+        expect(subject).to match_array(['test1', 'test2'])
+      end
+    end
+
+    context 'when SKIP_TENANTS is set' do
+      let(:skip_tenants_env_var) { 'test1,test2' }
+
+      it 'returns a subset of the Apartment list excluding names set by the env var' do
+        expect(subject).to match_array(['test3'])
+      end
+    end
+
+    context 'when ONLY_TENANTS and SKIP_TENANTS are set' do
+      let(:only_tenants_env_var) { 'test1' }
+      let(:skip_tenants_env_var) { 'test1' }
+
+      it 'prioritises the ONLY_TENANTS env var' do
+        expect(subject).to match_array(['test1'])
+      end
+    end
+  end
+end

spec/tenant_runner_spec.rb

@@ -20,16 +20,11 @@ module Tenant
     allow(Patches::Config.configuration).to receive(:application_version) { application_version }
   end
 
-  context 'with tenants' do
-    let(:tenants) { ['tenants'] }
-    subject { described_class.new(tenants: tenants) }
-    specify { expect(subject.tenants).to eql(tenants) }
-  end
-
   context 'perform' do
     let(:tenant_names) { ['test'] }
+    let(:tenant_finder) { double(Patches::TenantFinder, tenant_names: tenant_names) }
 
-    before { expect(Apartment).to receive(:tenant_names).and_return(tenant_names) }
+    before { allow(Patches::TenantFinder).to receive(:new).and_return(tenant_finder) }
 
     specify do
       expect(subject.tenants).to eql(['test'])