FEATURE: Allow a cluster_name to be configured and used for /srv/status (#12365)

The cluster name can be configured by setting the `DISCOURSE_CLUSTER_NAME` environment variable. If set, you can then call /srv/status with a `?cluster=` parameter. If the cluster does not match, an error will be returned. This is useful if you need a load balancer to be able to verify the identity, as well as the presence, of an application container.

spec/requests/forums_controller_spec.rb

@@ -37,4 +37,31 @@ RSpec.describe ForumsController do
     end
   end
 
+  describe "cluster parameter" do
+    it "returns a 500 response if the cluster is not configured" do
+      get "/srv/status?cluster=abc"
+      expect(response.status).to eq(500)
+      expect(response.body).to include("not configured")
+    end
+
+    it "returns a 500 response if the cluster does not match" do
+      global_setting(:cluster_name, "mycluster")
+      get "/srv/status?cluster=abc"
+      expect(response.status).to eq(500)
+      expect(response.body).to include("not match")
+    end
+
+    it "returns a 200 response if the cluster does match" do
+      global_setting(:cluster_name, "mycluster")
+      get "/srv/status?cluster=abc"
+      expect(response.status).to eq(500)
+      expect(response.body).to include("not match")
+    end
+
+    it "returns a 200 response when given shutdown_ok" do
+      get "/srv/status?shutdown_ok=1"
+      expect(response.status).to eq(200)
+    end
+  end
+
 end