Get remote address for runner

Check if `X-Forwarded-For` is set before getting the IP of the request,
with this the real IP address of the runner is shown if it's behind a
proxy.

closes https://gitlab.com/gitlab-org/gitlab-ce/issues/53676

changelogs/unreleased/53676-ip-address-of-gitlab-runner-is-wrong-in-the-runners-description.yml

+---
+title: Get remote IP address of runner
+merge_request: 24624
+author:
+type: changed

lib/api/helpers/runner.rb

@@ -26,7 +26,7 @@ module API
       end
 
       def get_runner_ip
-        { ip_address: request.ip }
+        { ip_address: request.env["HTTP_X_FORWARDED_FOR"] || request.ip }
       end
 
       def current_runner

spec/requests/api/runner_spec.rb

@@ -211,7 +211,7 @@ describe API::Runner, :clean_gitlab_redis_shared_state do
       it "sets the runner's ip_address" do
         post api('/runners'),
              params: { token: registration_token },
-          headers: { 'REMOTE_ADDR' => '123.111.123.111' }
+             headers: { 'X-Forwarded-For' => '123.111.123.111' }
 
         expect(response).to have_gitlab_http_status 201
         expect(Ci::Runner.first.ip_address).to eq('123.111.123.111')
@@ -520,7 +520,7 @@ describe API::Runner, :clean_gitlab_redis_shared_state do
           it "sets the runner's ip_address" do
             post api('/jobs/request'),
               params: { token: runner.token },
-              headers: { 'User-Agent' => user_agent, 'REMOTE_ADDR' => '123.222.123.222' }
+              headers: { 'User-Agent' => user_agent, 'X-Forwarded-For' => '123.222.123.222' }
 
             expect(response).to have_gitlab_http_status 201
             expect(runner.reload.ip_address).to eq('123.222.123.222')