Disable gitlab-workhorse static error page on health endpoints

app/controllers/health_controller.rb

@@ -41,6 +41,10 @@ class HealthController < ActionController::Base
       info[:labels] = r.labels if r.labels
       [name, info]
     end
+
+    # disable static error pages at the gitlab-workhorse level, we want to see this error response even in production
+    headers["X-GitLab-Custom-Error"] = 1 unless success
+
     render json: response.to_h, status: success ? :ok : :service_unavailable
   end
 end

changelogs/unreleased/ak-health-check-custom-error.yml

+---
+title: Disable gitlab-workhorse static error page on health endpoints
+merge_request: 17770
+author:
+type: fixed

spec/controllers/health_controller_spec.rb

@@ -30,6 +30,19 @@ describe HealthController do
         expect(json_response['shared_state_check']['status']).to eq('ok')
         expect(json_response['gitaly_check']['status']).to eq('ok')
       end
+
+      it 'responds with readiness checks data when a failure happens' do
+        allow(Gitlab::HealthChecks::Redis::RedisCheck).to receive(:readiness).and_return(Gitlab::HealthChecks::Result.new(false, "check error"))
+
+        subject
+
+        expect(json_response['redis_check']['status']).to eq('failed')
+        expect(json_response['redis_check']['message']).to eq('check error')
+        expect(json_response['cache_check']['status']).to eq('ok')
+
+        expect(response.status).to eq(503)
+        expect(response.headers['X-GitLab-Custom-Error']).to eq(1)
+      end
     end
 
     context 'accessed from whitelisted ip' do