Network Deployment (Distributed operating systems), v8.0 > Establishing high availability > Establishing high availability for Data access resources


Configure client reroute for applications that use DB2 databases

The client reroute feature enables you to configure your client applications for a DB2 universal database to recover from a communication loss, and the applications can continue to work with minimal interruption. Rerouting is central to the support of continuous operations, but rerouting is only possible when there is an alternate location that is identified to the client connection. This task assumes the following:

Client reroute for DB2 allows you to provide an alternate server location, in case the connection to the database server fails. If you decide to use client reroute with the persistence option, the alternate server information persists across Java Virtual Machines (JVMs). In the event of an application server crash, the alternate server information is not lost when the application server is restored and attempts to connect to the database.

Without any configuration on the client side, a JDBC driver for DB2 supports the client reroute capability, if it is enabled, when the driver makes an initial connection to the DB2 server. When the JDBC driver connects to a DB2 server that has an alternate server configured, the primary server sends information about the alternate server to the JDBC driver. If the connection to the primary server fails, the JDBC driver is able to reroute connections to the alternate server. If the client process crashes, however, the alternate server information is lost, and the client needs to connect to the primary server again. If the client cannot make an initial connection to the primary server, the client has no knowledge of the alternate server and cannot reroute.

To overcome this problem, you can configure a DB2 data source in the application server with the Alternate server name and Alternate port number fields, or with the clientRerouteAlternateServerName and clientRerouteAlternatePortNumber data source custom properties, to support client reroute even on the initial connection attempt. If the JDBC driver is not able to connect to the primary DB2 server, the information that is necessary for a client reroute is already present, and the JDBC driver can reroute the connection to an alternate server.

Attention: The data source custom property, enableClientAffinitiesList, changes the semantics of the clientRerouteAlternateServerName and clientRerouteAlternatePortNumber properties. To learn more about these properties, see the DB2 information center topic, Common IBM Data Server Driver for JDBC and SQLJ properties for all supported database products.

To learn more about client affinity, see the topic, .Configuring client affinity for applications that use DB2 databases.

Additionally, if we have configured a DB2 data source as a Type 4 JDBC driver, you can use the Client reroute server list JNDI name field, or the clientRerouteServerListJNDIName data source custom property, to enable persistence of the client reroute state. Typically, when a connection is rerouted and the JDBC driver has connected to the alternate DB2 server, the alternate server sends information about its own alternate server to the JDBC driver. The JDBC driver will then have the information that is required to reroute the connection again if the alternate DB2 server is not available. Effectively, the server that was originally the alternate server is now the primary server, and a new alternate server has been established. If you enable persistence for client reroute, this new state can be remembered. If the application server crashes and is restarted, the JDBC driver can connect to the DB2 server that was considered the primary server at the time of the crash. Without the persistence feature, the JDBC driver would have to start from the original server configuration and attempt to connect to the server that was originally considered the primary server.

We can use the automatic client rerouting feature within the following DB2 configurable environments:


Procedure

  1. In the administrative console, click Resources > JDBC > Data sources > data_source.

  2. Click WAS data source properties.

  3. In the DB2 automatic client reroute options section, fill in the fields to enable client rerouting. Complete the following fields:

    Alternate server names

    List of alternate server name or names for the DB2 server. If more than one alternate server name is specified, the names must be separated by commas. For example: 
     host1,host2

    Alternate port numbers

    List of alternate server port or ports for the DB2 server. If more than one alternate server port is specified, the ports must be separated by commas. For example: 
    5000,50001
    Ensure that an equal number of entries must be specified for both alternate ports and hosts. Otherwise, a warning is displayed and client reroute is not enabled.

  4. Optional: Enable client reroute with the persistence option.

    1. Complete the field for Client reroute server list JNDI name. The field specifies the JNDI name used to bind the DB2 client reroute server list into the JNDI name space. The DB2 database server uses this name to look up the alternate server name list when the alternate server information is not already in memory. Be aware of the following:

      • This option is not supported for Type 2 data sources. If you use a DB2 data source that is configured as a Type 2 JDBC driver, the JDBC driver uses a catalog to persist the client reroute information. If this property is configured with a Type 2 driver, the application server will issue a warning.

      • Use different JNDI names among different data sources. Otherwise, when you delete a data source, and the JNDI entry is removed from the name space, the other data sources that share the JNDI entry will be affected.

  5. Configure the retry count and interval for the client reroute function. Complete these two fields:

    Retry interval for client reroute

    Amount of time, in seconds, between retries for automatic client reroute.

    Maximum retries for client reroute

    Maximum number of connection retries that are attempted by the automatic client reroute function if the primary connection to the server fails. The property is only used when Retry interval for client reroute is set.

    If you do not specify a value for these properties, DB2 failover processing (client rerouting) does not occur.

  6. Click OK and save the changes.

  7. Restart the application server.


What to do next

If you later want to remove the client reroute information that is bound in JNDI, you can do so by deleting the data source. We can also use the unbind feature with the test connection service to delete the JNDI binding for the client reroute function from the application server's JNDI name space without deleting the data source.

To delete the JNDI binding for client reroute:

  1. Select Unbind client reroute list from JNDI.

  2. Click OK.

  3. Save the configuration.

  4. Click Test connection for the data source.
  5. Deselect Unbind client reroute list from JNDI.

  6. Click OK.

  7. Save the configuration.


Configure a JDBC provider and data source
Configure a data source
Configure client affinities for applications that use DB2 databases
Configuration of client affinities for Java clients for DB2 Database for Linux, UNIX, and Windows connections
Common IBM Data Server Driver for JDBC and SQLJ properties for all supported database products
IBM DB2 Driver for JDBC and SQLJ client reroute support
IBM WebSphere Developer Technical Journal: Building a high availability database environment using WebSphere middleware, Part 1

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