Merge branch '4934-improve-bring-a-demoted-primary-back-online' into 'master'

Improve "Bring a demoted primary back online" documentation

Closes #4934

See merge request gitlab-org/gitlab-ee!4578

doc/administration/geo/disaster_recovery/bring_primary_back.md

@@ -6,6 +6,8 @@ restore your original configuration. This process consists of two steps:
 1. Making the old primary a secondary
 1. Promoting a secondary to a primary
 
+> *Warning:* If you have any doubts about the consistency of the data on this node, we recommend to set up it from scratch.
+
 ## Configure the former primary to be a secondary
 
 Since the former primary will be out of sync with the current primary, the first step is
@@ -23,12 +25,16 @@ To bring the former primary up to date:
     sudo gitlab-ctl start
     ```
 
-    NOTE: **Note:** If you [disabled primary permanently][disaster-recovery-disable-primary], 
+    >**Note 1:** If you [disabled primary permanently][disaster-recovery-disable-primary],
     you need to undo those steps now. For Debian/Ubuntu you just need to run
-    `sudo systemctl enable gitlab-runsvdir`. For CentoOS 6, you need to install
+    `sudo systemctl enable gitlab-runsvdir`. For CentOS 6, you need to install
     the GitLab instance from scratch and setup it as a secondary node by
-    following [Setup instructions][setup-geo].
-    In this case you don't need to follow the next step.
+    following [Setup instructions][setup-geo].  In this case you don't need to follow the next step.
+
+    >**Note 2:** If you [changed the DNS records](index.md#step-4-optional-updating-the-primary-domains-dns-record)
+    for this node during disaster recovery procedure you may need to [block
+    all the writes to this node](https://gitlab.com/gitlab-org/gitlab-ee/blob/master/doc/gitlab-geo/planned-failover.md#block-primary-traffic)
+    during this procedure.
 
 1. [Setup database replication][database-replication]. Note that in this
    case, primary refers to the current primary, and secondary refers to the