|
Oracle® Internet Directory Administrator's Guide,
10g Release 2 (10.1.2) Part No. B14082-01 |
|
 Previous |
 Next |
|
Oracle® Internet Directory Administrator's Guide,
10g Release 2 (10.1.2) Part No. B14082-01 |
|
|
Previous |
Next |
This chapter explains the Oracle Application Server Cold Failover Cluster (Identity Management), one of the high availability configurations for Oracle Internet Directory.
This chapter contains these topics:
About the Oracle Application Server Cold Failover Cluster (Identity Management)
Installing Oracle Application Server Cold Failover Cluster (Identity Management)
A cluster is a collection of interconnected usable whole computers that is used as a single computing resource. Hardware clusters provide high availability and scalability.
During failover, an application running on one cluster node is transparently migrated to another cluster node. During this migration, clients accessing the service on the cluster see a momentary outage and may need to reconnect once the failover is complete.
The cluster node on which the application runs at any given time is called the primary node. The cluster node to which the application is moved during a failover is called the secondary node.
In a hardware cluster, each physical node has its own physical IP address and physical host name. To present a single system image to the outside world, the cluster uses a dynamic IP address that can be moved to any physical node in the cluster. This is called the virtual IP address. The host name corresponding to this virtual IP address is called the logical or virtual host name. All network clients accessing a service on the cluster in a cold failover configuration use the virtual host name.
A logical host consists of one or more disk groups, and pairs of host names and IP addresses. It is mapped to a physical host in the cluster. This physical host impersonates the host name and IP address of the logical host.
Although each node is a usable whole computer, in most cases the storage subsystem is shared by all the nodes. In a Oracle Application Server Cold Failover Cluster (Identity Management) configuration, the shared storage subsystem hosts the Oracle Internet Directory installation—that is, the ORACLE_HOME—and at any given point in time is accessible by one active node.
For information about installing a cold Oracle Application Server Cold Failover Cluster (Identity Management) configuration like the one described in the next section, see the section "Installing a Distributed OracleAS Cold Failover Cluster (Identity Management) Configuration" in the chapter "Installing in HA Environments: OracleAS Cold Failover Cluster" in Oracle Application Server Installation Guide.
Figure 28-1 shows a simple cold failover configuration in which an unspecified number of LDAP clients connect to Physical Host A and Physical Host B.
In Figure 28-1 the primary cluster node is Physical Host A and the secondary cluster node is Physical Host B. There is only one software and database installation. Physical hosts A and B have access to the shared disk on which the Oracle Internet Directory software and database reside.
Physical host A is configured to host the virtual host VH and the installation on the virtual host VH. The Oracle Internet Directory processes are started on the virtual host VH. All LDAP clients talk to Oracle Internet Directory by using the virtual host name VH.
This section contains these topics:
You can start Oracle Internet Directory servers on virtual hosts by using either OID Monitor (oidmon) and OID Control Utility (oidctl), or by using the Oracle Directory Integration and Provisioning Server Registration Tool (odisrvreg).
When using the Oracle Directory Integration and Provisioning Server Registration Tool (odisrvreg), use the lhost parameter to specify the virtual host name.
|
See Also:
|
To illustrate the cold failover process, Figure 28-2 shows the same environment as that in Figure 28-1 but with Physical Host A having failed.
As Figure 28-2 shows, when Physical Host A fails or is shut down for maintenance purposes, the virtual host VH is migrated to Physical Host B. After the failover, you must restart the Oracle Database, the listener, and Oracle Internet Directory.
To automate the failover, you can write vendor-specific scripts to start the required processes. To effect transparent failover semantics, direct the cluster software to invoke the scripts.
After failover, LDAP clients continue to communicate with the same host as before, namely, the virtual host, VH. Consequently, the service disruption for these clients is minimal. The clients must reconnect when the failover is complete.
To provide additional availability and scalability, you can use the cold failover technique in conjunction with Oracle Internet Directory Replication. Figure 28-3 illustrates this configuration.
As Figure 28-3 shows, on a two node cluster:
Virtual Host VHA is hosted by Physical Host A.
Virtual Host VHB is hosted by Physical Host B.
Oracle Internet Directory Node 1 is installed and configured on Virtual host VHA.
Oracle Internet Directory Node 2 is installed and configured on Virtual Host VHB.
Both Oracle Internet Directory nodes are configured for multimaster replication.
LDAP applications can do either of the following:
Communicate directly with either Oracle Internet Directory node by using the respective virtual host names for the LDAP host
Load-balance by means of a LAN re-director or another third-party solution that connects to the two hosts on which the Oracle Internet Directory nodes are configured
Using cold failover in this way represents an improvement over the simple cold failover configuration. There are two Oracle Internet Directory nodes and the two are in multimaster replication. Oracle Internet Directory is active on both cluster nodes and hence presents an active-active configuration. In contrast to the cold failover-only configuration, which is an active-passive configuration, the Oracle Internet Directory services are actively available on both cluster nodes at any given point in time.
Figure 28-4 shows the cold failover process in conjunction with Oracle directory replication.
As Figure 28-4 shows, when Physical Host A fails or is unavailable because of maintenance downtime, the cluster software fails over virtual host VHA to Physical Host B. The Oracle Internet Directory processes that were previously running on Physical Host A are then restarted on Virtual Host VHA, and replication is resumed.
LDAP applications communicating directly with Oracle Internet Directory Node 1 by using host name VHA experience a momentary service outage. After the failover is complete, these applications must reconnect by using the same host name, namely, VHA. The momentary LDAP outage can be avoided completely if the two Oracle Internet Directory nodes are front-ended by a LAN redirector for load balancing.
