diff --git a/docs/07-bootstrapping-etcd.md b/docs/07-bootstrapping-etcd.md
index 1de9616..2a01a4c 100644
--- a/docs/07-bootstrapping-etcd.md
+++ b/docs/07-bootstrapping-etcd.md
@@ -117,4 +117,6 @@ sudo ETCDCTL_API=3 etcdctl member list \
 54a5796a6803f252, started, master-1, https://192.168.5.11:2380, https://192.168.5.11:2379
 ```
 
+Reference: https://kubernetes.io/docs/tasks/administer-cluster/configure-upgrade-etcd/#starting-etcd-clusters
+
 Next: [Bootstrapping the Kubernetes Control Plane](08-bootstrapping-kubernetes-controllers.md)