To install a flex cluster (or a flex ASM)  Grid Naming Service (GNS) is required. A GNS can be configured with dynamic public networks (DHCP) for VIP. This method is suitable for a big number of nodes.In this case GNS domain delegation is mandatory.
In case of a few number of nodes, GNS can be configured without domain delegation. In this case we have to define manually all VIP addresses (like in a standard cluster)

In this article we will briefly show how to install a two nodes flex cluster (we suppose we are  familiar with standard cluster installation). We will just insist in supplementary steps to configure a flex cluster. A GNS without Subdomain will be used.

What do we need ?

1- A DNS server to resolve all addresses

2- Two servers: rac12a.localdomain and rac12b.localdomain with 1 public address, 1 virtual address and 1 private address for each node

3- A GNS Subdomain: gns.localdomain  resolved by 1 address in the public subnet  in  the  DNS

4- A scan name : racscan.gns.localdomain resolved by 3 addresses in the public subnet. Note that the name of the scan should contain the GNS subdomain name gns.localdomain.

We present below all IP addresses we use for our flex cluster


To start installation we have to launch the  ./runInstaller file. Below we will not present all screen shots of the installation. We  only show the ones which are different from the standard installation




Click Next



We choose Configure a flex cluster


In this step we have info about GNS  and SCAN configuration. Note that We check Configure GNS and that we don’t choose Dynamic Networks. Note also that the scan name is including the GNS Subdomain name.


Here we can choose to  configure a hub node or a leaf node.


In this step we have to specify network for public, private and ASM.

The remaining steps are same than in a standard installation and will not be shown here

Once install done successfully we can verify the mode of the cluster

[[email protected] ~]$ crsctl get cluster mode status
Cluster is running in "flex" mode
[[email protected] ~]$

We can see that a GNS is configured

[[email protected] ~]$ srvctl config gns
GNS is enabled.
GNS VIP addresses:
Domain served by GNS: gns.localdomain
[[email protected] ~]$


The following shows that there is a flex ASM running

 [[email protected] ~]$ asmcmd showclustermode
ASM cluster : Flex mode enabled
[[email protected] ~]


In a future article  we will see how flex ASM works and what are the benefits

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Mouhamadou Diaw