Replacing a cluster node

To replace a GitHub Enterprise Server node, you must mark the affected nodes offline in the cluster configuration file (cluster.conf) and add the replacement nodes. This might be necessary if a node were to fail, or to add a node with more resources to increase performance.

Warning: The replacement node must use a hostname that has not been used previously in the cluster to avoid conflicts.

Provision and install GitHub Enterprise Server with a unique hostname on the replacement node.
Using the administrative shell or DHCP, only configure the IP address of the replacement node. Don't configure any other settings.
To mark the failed node offline, on any node, modify the cluster configuration file (cluster.conf) in the relevant node section to include the text offline = true.

For example, this modified cluster.conf will mark the ghe-data-node-3 node as offline:
```
  [cluster "ghe-data-node-3"]
    hostname = ghe-data-node-3
    offline = true
    ipv4 = 192.168.0.6
    # ipv6 = fd12:3456:789a:1::6
```
From the administrative shell of the node where you modified cluster.conf, run ghe-cluster-config-apply. This will validate the configuration file, copy it to each node in the cluster, and mark the node offline.

To add the newly provisioned replacement node, on any node, modify the cluster.conf file to remove the failed node and add the replacement node. For example, this modified cluster.conf file replaces ghe-data-node-3 with the newly provisioned node, ghe-replacement-data-node-3:

[cluster "ghe-replacement-data-node-3"]
  hostname = ghe-replacement-data-node-3
  ipv4 = 192.168.0.7
  # ipv6 = fd12:3456:789a:1::7
  git-server = true
  pages-server = true
  mysql-server = true
  elasticsearch-server = true
  redis-server = true
  memcache-server = true
  metrics-server = true
  storage-server = true

If you're replacing the MySQL master node or Redis master node, in cluster.conf, modify the mysql-master or redis-master value with the replacement node name.

For example, this modified cluster.conf file specifies a newly provisioned cluster node, ghe-replacement-data-node-1 as the MySQL and Redis master node:
```
  mysql-master = ghe-replacement-data-node-1
  redis-master = ghe-replacement-data-node-1
```
From the administrative shell of the node with the modified cluster.conf, run ghe-cluster-config-init. This will initialize the newly added node in the cluster.
From the same node, run ghe-cluster-config-apply. This will validate the configuration file, copy it to each node in the cluster, and configure each node according to the modified cluster.conf file.

Replacing a cluster node

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