Allow to use ENV variables in redis config

changelogs/unreleased/env-var-in-redis-config.yml

+---
+title: Allow to use ENV variables in redis config
+merge_request: 8073
+author: Semyon Pupkov

doc/install/installation.md

@@ -601,6 +601,12 @@ If you want to connect the Redis server via socket, then use the "unix:" URL sch
     production:
       url: unix:/path/to/redis/socket
 
+Also you can use environment variables in the `config/resque.yml` file:
+
+    # example
+    production:
+      url: <%= ENV.fetch('GITLAB_REDIS_URL') %>
+
 ### Custom SSH Connection
 
 If you are running SSH on a non-standard port, you must change the GitLab user's SSH config.

lib/gitlab/redis.rb

@@ -42,7 +42,7 @@ module Gitlab
         return @_raw_config if defined?(@_raw_config)
 
         begin
-          @_raw_config = File.read(CONFIG_FILE).freeze
+          @_raw_config = ERB.new(File.read(CONFIG_FILE)).result.freeze
         rescue Errno::ENOENT
           @_raw_config = false
         end

spec/fixtures/config/redis_config_with_env.yml

+test:
+  url: <%= ENV['TEST_GITLAB_REDIS_URL'] %>

spec/lib/gitlab/redis_spec.rb

 require 'spec_helper'
 
 describe Gitlab::Redis do
-  let(:redis_config) { Rails.root.join('config', 'resque.yml').to_s }
+  include StubENV
 
   before(:each) { clear_raw_config }
   after(:each) { clear_raw_config }
@@ -72,6 +72,20 @@ describe Gitlab::Redis do
 
       expect(url2).not_to end_with('foobar')
     end
+
+    context 'when yml file with env variable' do
+      let(:redis_config) { Rails.root.join('spec/fixtures/config/redis_config_with_env.yml') }
+
+      before  do
+        stub_env('TEST_GITLAB_REDIS_URL', 'redis://redishost:6379')
+      end
+
+      it 'reads redis url from env variable' do
+        stub_const("#{described_class}::CONFIG_FILE", redis_config)
+
+        expect(described_class.url).to eq 'redis://redishost:6379'
+      end
+    end
   end
 
   describe '._raw_config' do