38 Setting Up Replication Failover

This Chapter contains the following topics:

38.1 Introduction to Replication Failover

Since 10g (10.1.4.0.1), Oracle Internet Directory has supported failover of LDAP replicas from one supplier to another. Administrator intervention is required. Figure 38-1 shows a typical failover scenario.

Figure 38-1 Replication Failover Scenario

Described in text

This scenario has the following features:

  • Apple, Banana and Candy are multimaster replicas in the same DRG.

  • Damson is a read-only fan-out replica of Banana. That is, it is a partial replica using one-way LDAP replication.

  • Eggplant is an updatable fan-out replica of Banana. That is, it is a partial replica using two-way LDAP replication.

  • If Banana goes down, replication between the multimaster DRG and its fan-out replicas is broken.

    An administrator can switch Eggplant and Damson to a new supplier, Candy.

Only two failover topology types are supported:

  • The consumer and new supplier are both connected to the old supplier with LDAP-based replication agreements. This is shown in Figure 38-2. Node 1 and Node 3 both have LDAP replication agreements with Node 2. Node 2 is the original supplier for Node 1. When Node 2 fails, you can fail over Node 1 to a new supplier, Node 3.

    Figure 38-2 Consumer and New Supplier Connected to Old Supplier by LDAP

    Described in Text

  • The consumer is connected to the old supplier with an LDAP-based agreement and the old supplier is in the same Advanced Replication group as the new supplier. This is shown in Figure 38-3. Node 2 and Node 3 are in the same Advanced Replication DRG. Node 2 is the original supplier for Node 4. When Node 4 fails, you can fail over Node 4 to a new supplier, Node 3.

    Figure 38-3 Old and New Suppliers in the Same Advanced Replication Group

    Described in text

38.1.1 Limitations and Warnings for Replication Failover

This section describes limitations and warnings related to the use of replication failover.

  • As of Oracle Internet Directory 11g Release 1 (11.1.1), replication failover requires administrator intervention.

  • Following failover, you must compare and reconcile the consumer with the new supplier.

  • The new agreement must be of the same type and direction as the old agreement.

  • Only two topology types are supported.

  • When a supplier fails, its directly connected replica can only fail over to another directly connected replica of the failed supplier.

  • The replication filtering policy for the agreement between the new supplier and old supplier must match that between the old supplier and consumer.

  • In most cases, you should fail over the replica in a way that preserves the original replica type. In the case shown in Figure 38-4, node 2 is the old supplier for both node 1 and 3, and node 1 is read-only. When node 2 fails, you could, in theory, set up either node 1 or 3 as the new supplier node. Best practice, however, is to fail over node 1 so that node 3 is the supplier. This preserves node 1's original, read-only replica type.

    Figure 38-4 Failover Preserving Replica Type

    Described in text

  • If the new agreement is a two-way agreement, after you compare and reconcile the consumer with its new supplier, you must also compare and reconcile all other replicas that are connected to the new supplier with the new supplier. For example, in Figure 38-5, Node 2 has a two-way agreement with Node 3. Node 3 is connected to another replica, Node 4. When Node 2 fails, you set up a two-way agreement between node 3 and node 1. After comparing and reconciling node 3 with node 1, you must also compare and reconcile Node 4 with node 3 to ensure that the replicas are synchronized.

    Figure 38-5 Compare and Reconcile All Connected Replicas

    Described in text

38.1.2 Determining Which Type of Replication Failover to Use

There are two types of replication failover. They are:

  • Stateless

  • Time-based

Use stateless failover when you are unable to plan for the failover in advance. Stateless replication failover makes no assumptions about the state of the replicas. You can fail over to a new supplier at any time. Stateless failover requires more work after failover to synchronize the nodes.

Use time-based failover for planned failover. Time-based failover results in less work after failover. However, it requires some setup ahead of time to ensure that the following assumptions are true at the time of failover:

  • The nodes are mostly synchronized

  • The new supplier has preserved its change logs so that complete synchronization can be achieved quickly.

38.2 Performing a Stateless Replication Failover

This section explains how to perform a stateless replication failover. It consists of the following tasks:

38.2.1 Task 1: Stop all Directory Replication Server on related Nodes

Stop the Oracle directory replication servers on the new supplier, old supplier and consumer, by typing:

oidctl connect=connStr server=oidrepld instance=1 componentname=oidComponentName \
 flags="-h LdapHost -p LdapPort" stop

38.2.2 Task 2: Break Old Replication Agreement and Set up New Agreement

Break the old replication agreement between the old supplier and consumer and set up a new agreement between the new supplier and consumer. Do this by using the Replication Environment Management Tool. Type:

remtool -pchgmaster [-v] [-bind consumer_host::port_number]

you are prompted for the replication_dn_password.

See Also:

The remtool command-line tool reference in Oracle Fusion Middleware User Reference for Oracle Identity Management

38.2.3 Task 3: Save Last Change Number

Obtain the last change number from the new supplier.

For a one-way agreement, use the following command:

ldapsearch -h new_supplier_host -p port_number -b "" \
   -s base "objectclass=*" lastchangenumber

For a two-way agreement, use the following command:

ldapsearch -h consumer_host -p port_number -b "" \
   -s base "objectclass=*" lastchangenumber

Save this number!

38.2.4 Task 4: Compare and Reconcile New Supplier and Consumer

Use the Oracle Internet Directory Comparison and Reconciliation Tool to compare and reconcile the new supplier and consumer. For a one-way agreement, type:

oidcmprec operation=reconcile \
   source=new_supplier_host:port \
   destination=consumer_host:port \
   base='""' scope=sub

For a two-way agreement, type:

oidcmprec operation=merge \
   source=new_supplier_host:port\
   destination=consumer_host:port/ \
   base='""' scope=sub

you are prompted for the source and destination replication dn passwords.

This example assumes that the entire directory is replicated and, therefore, that base is set to " ". If you are using partial replication, use the base and dns2exclude arguments to the oidcmprec tool to include the desired DIT.

See Also:

The oidcmprec command-line tool reference in Oracle Fusion Middleware User Reference for Oracle Identity Management

38.2.5 Task 5: Update Last Applied Change Number of New Agreement

Modify the new agreement with the retrieved last applied number at the new supplier. To do this:

  1. Create an LDIF file with the last change number you retrieved in "Task 3: Save Last Change Number".

    For a one-way agreement, it should look similar to this:

    dn: agreement_dn
changetype: modify
replace: orclLastAppliedChangeNumber;apply$new_supplier_host$consumer_host
 orclLastAppliedChangeNumber;apply$new_supplier_host$consumer_host: 
 last_change_number_retrieved.
-
replace: orclLastAppliedChangeNumber;transport$new_supplier_host$consumer_host
orclLastAppliedChangeNumber;transport$new_supplier_host$consumer_host: 
 last_change_number_retrieved_from_new_supplier

    For a two-way agreement, it should look similar to this:

    dn: agreement_dn
changetype: modify
replace: orclLastAppliedChangeNumber;apply$new_supplier_host$consumer_host
orclLastAppliedChangeNumber;apply$new_supplier_host$consumer_host: 
 last_change_number_retrieved_from_new_supplier
-
replace: orclLastAppliedChangeNumber;transport$new_supplier$consumer
orclLastAppliedChangeNumber;transport$new_supplier$consumer: 
 last_change_number_retrieved_from_new_supplier   
-
replace: orclLastAppliedChangeNumber;apply$consumer_host$new_supplier_host
orclLastAppliedChangeNumber;apply$consumer_host$new_supplier_host: 
 last_change_number_retrieved_from_consumer      
-
replace: orclLastAppliedChangeNumber;transport$consumer_host$new_supplier_host
orclLastAppliedChangeNumber;transport$consumer_host$new_supplier_host:
 last_change_number_retrieved_from_consumer

  2. Modify the agreement by using ldapmodify, as follows:

    ldapmodify -D "cn=orcladmin" -q -h host_name -p port_number -f LDIF_file

38.2.6 Task 6: Clean Up Old Agreement on Old Supplier

If the old supplier was down when you performed "Task 2: Break Old Replication Agreement and Set up New Agreement", the old agreement on the old supplier was not cleaned up. Clean it up now by using the Replication Environment Management Tool. Type:

remtool -pcleanup -agrmt [-v] [-bind consumer_host::port_number]

you are prompted for the replication_dn_password.

See Also:

The remtool command-line tool reference in Oracle Fusion Middleware User Reference for Oracle Identity Management

38.2.7 Task 7: Start All Directory Replication Server on related Nodes

Start the Oracle directory replication servers on the new supplier, the old supplier and the consumer, by typing:

oidctl connect=connStr server=oidrepld instance=1 \
   name=instance_name componentname=component_name \
   flags="-h LdapHost -p LdapPort" start

See Also:

Chapter 4, "Understanding Process Control of Oracle Internet Directory Components"

38.3 Performing a Time-Based Replication Failover

This section explains how to perform a time-based replication failover. It contains these topics:

38.3.1 Task 1: Configure Change Log Garbage Collection Object on New Supplier

Configure the changelog purging configuration entry on the new supplier so that it preserves change logs for the desired period, for example, 24 hours, as follows:

  1. Create an LDIF file similar to this:

    dn: cn=changelog purgeconfig,cn=purgeconfig,cn=subconfigsubentry
changetype:modify
replace: orclpurgetargetage
orclpurgetargetage: 24

  2. Apply the LDIF file by typing:

    ldapmodify -D "cn=orcladmin" -q -p port -h host -D dn -f LDIF_file

See Also:

Chapter 34, "Managing Garbage Collection"

38.3.2 Task 2: Save Last Change Number from New Supplier

Obtain the last change number from the new supplier, as follows:

ldapsearch -h new_supplier_host -p port_number -D cn=orcladmin -q \
   -b "" -s base "objectclass=*" lastchangenumber

Save this number!

38.3.3 Task 3: Enable Change Log Regeneration on New Supplier

Enable change log regeneration at the new supplier, as follows:

  1. Create an LDIF file like this:

    dn: 
changetype: modify
replace: orcldiprepository
orcldiprepository: TRUE

  2. Apply the LDIF file by typing:

    ldapmodify -D "cn=orcladmin" -q -h host_name -p port_number -f LDIF_file

38.3.4 Task 4: Wait for the Desired Time Period to Elapse

Wait for a period no greater than the value of orclpurgetargetage in the changelog purging configuration entry.

38.3.5 Task 5: Stop all Directory Replication Servers on Related Nodes

Stop the Oracle directory replication servers on the new supplier, old supplier and consumer, by typing:

oidctl connect=connStr server=oidrepld instance=1 \
 componentname=oidComponentName \
 flags="-h LdapHost -p LdapPort" stop

See Also:

Chapter 4, "Understanding Process Control of Oracle Internet Directory Components"

38.3.6 Task 6: Break Old Replication Agreement and Set Up New Agreement

Break the old replication agreement between the old supplier and the consumer, then set up a new agreement between the new supplier and the consumer. Do this by using the Replication Environment Management Tool, as follows:

remtool -pchgmaster [-v] [-bind hostname:port_number]

you are prompted for the replication_dn_password.

See Also:

The remtool command-line tool reference in Oracle Fusion Middleware User Reference for Oracle Identity Management

38.3.7 Task 7: Update Last Applied Change Number of New Agreement

Modify the new agreement at the new supplier so that its last applied change number has the value you retrieved in "Task 2: Save Last Change Number from New Supplier", as follows:

  1. Create an LDIF file with the retrieved last applied change number, similar to this:

    dn: agreement_dn
changetype: modify
replace: orclLastAppliedChangeNumber
orclLastAppliedChangeNumber: last_change_number_retrieved

  2. Apply the LDIF file to the agreement by using ldapmodify:

    ldapmodify -D "cn=orcladmin" -q -h host_name -p port_number -f LDIF_file

38.3.8 Task 8: Clean Up Old Agreement on Old Supplier

If the old supplier was down when you performed "Task 6: Break Old Replication Agreement and Set Up New Agreement", the old agreement on the old supplier was not cleaned up. Clean it up now by using the Replication Environment Management Tool. Type:

remtool -pcleanup -agrmt [-v] [-bind hostname:port_number]

you are prompted for the replication_dn_password.

See Also:

The remtool command-line tool reference in Oracle Fusion Middleware User Reference for Oracle Identity Management

38.3.9 Task 9: Start All Directory Replication Servers on Related Nodes

Start the Oracle directory replication servers on the new supplier, the old supplier and the consumer, by typing:

oidctl connect=connStr server=oidrepld instance=1  \
 componentname=oidComponentName \
 flags="-h LdapHost -p LdapPort" start

See Also: