Revive articles about configuring high availability for a cluster (#4…

…1265)

Co-authored-by: Matt Pollard <mattpollard@users.noreply.github.com>

content/admin/monitoring-managing-and-updating-your-instance/configuring-clustering/about-clustering.md

@@ -8,12 +8,6 @@ redirect_from:
   - /enterprise/admin/clustering/clustering-overview
   - /enterprise/admin/enterprise-management/about-clustering
   - /admin/enterprise-management/about-clustering
-  - /enterprise/admin/enterprise-management/configuring-high-availability-replication-for-a-cluster
-  - /admin/enterprise-management/configuring-high-availability-replication-for-a-cluster
-  - /admin/enterprise-management/configuring-clustering/configuring-high-availability-replication-for-a-cluster
-  - /enterprise/admin/enterprise-management/initiating-a-failover-to-your-replica-cluster
-  - /admin/enterprise-management/initiating-a-failover-to-your-replica-cluster
-  - /admin/enterprise-management/configuring-clustering/initiating-a-failover-to-your-replica-cluster
   - /admin/enterprise-management/configuring-clustering/about-clustering
 versions:
   ghes: '*'

content/admin/monitoring-managing-and-updating-your-instance/configuring-clustering/index.md

@@ -24,4 +24,6 @@ children:
   - /rebalancing-cluster-workloads
   - /evacuating-a-cluster-node-running-data-services
   - /replacing-a-cluster-node
+  - /configuring-high-availability-replication-for-a-cluster
+  - /initiating-a-failover-to-your-replica-cluster
 ---

content/admin/monitoring-managing-and-updating-your-instance/configuring-clustering/initiating-a-failover-to-your-replica-cluster.md

@@ -0,0 +1,42 @@
+---
+title: Initiating a failover to your replica cluster
+intro: 'If your {% data variables.product.prodname_ghe_server %} cluster fails, you can fail over to the replica.'
+redirect_from:
+  - /enterprise/admin/enterprise-management/initiating-a-failover-to-your-replica-cluster
+  - /admin/enterprise-management/initiating-a-failover-to-your-replica-cluster
+versions:
+  ghes: '>= 3.9'
+type: how_to
+topics:
+  - Clustering
+  - Enterprise
+  - High availability
+  - Infrastructure
+shortTitle: Initiate a failover to replica
+---
+
+## About failover to your replica cluster
+
+If the datacenter for your active cluster experiences a failure and you've configured high availability, you can fail over to your replica cluster.
+
+Failing over to your replica cluster promotes it to be your new active cluster, and decouples the new active cluster from the old active cluster. After failover, you will have two standalone clusters without high availability configured. You can reconfigure replication from the new active cluster. For more information, see "[AUTOTITLE](/enterprise/admin/enterprise-management/configuring-high-availability-replication-for-a-cluster#reconfiguring-high-availability-replication-after-a-failover)."
+
+## Prerequisites
+
+To fail over to replica nodes, you must have configured high availability replication for your cluster. For more information, see "[AUTOTITLE](/enterprise/admin/enterprise-management/configuring-high-availability-replication-for-a-cluster)."
+
+{% data reusables.enterprise_clustering.high-availability-requires-391 %}
+
+## Initiating a failover to your replica cluster
+
+1. SSH into the primary MySQL node in the replica cluster. For more information, see "[AUTOTITLE](/enterprise/admin/configuration/accessing-the-administrative-shell-ssh#enabling-access-to-the-administrative-shell-via-ssh)."
+1. To begin the failover to the secondary cluster and configure the nodes to respond to requests, run the following command.
+
+    ```shell
+  ghe-cluster-failover
+  ```
+
+{% data reusables.enterprise_clustering.configuration-finished %}
+1. Update the DNS record to point to the IP address of the load balancer for your replica cluster. After the TTL period expires, requests will be directed to the replica cluster.
+
+After {% data variables.product.prodname_ghe_server %} returns you to the prompt and your DNS updates propagate, you've finished failing over. Users can access {% data variables.product.prodname_ghe_server %} using the usual hostname for your cluster.

data/release-notes/enterprise-server/3-9/1.yml

@@ -96,6 +96,8 @@ sections:
       The Management Console displays a warning about unexpected consequences that may result from modification of the instance's hostname after initial configuration.
     - |
       On an instance with multiple nodes, internal tooling to repair repositories now attempts to resolve problems within the entire repository network.
+    - |
+      To supplement a disaster recovery plan for a GitHub Enterprise Server instance in a cluster configuration, an administrator can configure a replica of an entire cluster in a separate datacenter, allowing the cluster to fail over to redundant nodes. For more information, see "[AUTOTITLE](/admin/monitoring-managing-and-updating-your-instance/configuring-clustering/configuring-high-availability-replication-for-a-cluster)."
   known_issues:
     - |
       {% data reusables.release-notes.upgrade-to-3-9-or-to-3-10-io-utilization-increase %}

data/reusables/enterprise/use-a-multiplexer.md

@@ -0,0 +1 @@
+This command can take some time to finish, so we recommend running the command in a terminal multiplexer like `screen` or `tmux`.

data/reusables/enterprise_clustering/apply-configuration.md

@@ -0,0 +1,3 @@
+1. Apply the new configuration. {% data reusables.enterprise.use-a-multiplexer %}
+
+        ghe-cluster-config-apply

data/reusables/enterprise_clustering/configuration-file-heading.md

@@ -0,0 +1 @@
+The cluster configuration file lists each node under a <code>[cluster "<em>HOSTNAME</em>"]</code> heading.

data/reusables/enterprise_clustering/configuration-finished.md

@@ -0,0 +1,5 @@
+1. After the configuration run finishes, {% data variables.product.prodname_ghe_server %} displays the following message.
+
+    ```shell
+    Finished cluster configuration
+    ```

data/reusables/enterprise_clustering/high-availability-requires-391.md

@@ -0,0 +1,9 @@
+{% ifversion ghes = 3.9 %}
+
+{% note %}
+
+**Note:** High availability replication is available on {% data variables.product.prodname_ghe_server %} version 3.9.1 and later. 
+
+{% endnote %}
+
+{% endif %}

data/reusables/enterprise_clustering/key-value-pair-order-irrelevant.md

@@ -0,0 +1 @@
+The order of the key-value pairs doesn't matter.

data/reusables/enterprise_clustering/network-latency.md

@@ -1 +1 @@
-For high availability, the latency between the network with the active nodes and the network with the passive nodes must be less than 70 milliseconds. We don't recommend configuring a firewall between the two networks.
+For high availability, the latency between the network with the active nodes and the network with the replica nodes must be less than 70 milliseconds. We don't recommend configuring a firewall between the two networks.

data/reusables/enterprise_clustering/open-configuration-file.md

@@ -0,0 +1,5 @@
+1. Open the cluster configuration file at `/data/user/common/cluster.conf` in a text editor. For example, you can use Vim. Create a backup of the `cluster.conf` file before you edit the file.
+
+   ```shell copy
+   sudo vim /data/user/common/cluster.conf
+   ```