The goal of high availability is to provide a backup mechanism to transfer requests and data processing to a standby system in the event of primary system failure; however, user and system requirements vary. There is no one ideal configuration and so you must carefully consider the settings based on the system performance, availability, scalability, and reliability.
In this article we'll provide a number of recommendations for setting up and maintaining the Cognos solution for high availability and for disaster recovery, including:
- Cognos gateways and Cognos application servers.
- Active and standby Cognos Content Manager.
- IBM® DB2® High Availability and Disaster Recovery (HADR).
For more on installing and configuring Cognos in the IBM Cloud, see the rest of this series and the Cognos site (Resources).
Cognos gateways and Cognos application servers
To achieve failover support at the gateway layer, install multiple Cognos gateways onto a web farm, one on each web server. The web farm entry point (commonly a router or reverse proxy server) should be able to re-route requests to the next available web server in the event of web server failure (as in Figure 1).
Figure 1. A high-availability Cognos cloud environment with a reverse proxy router
We recommend that each Cognos gateway be configured with multiple Cognos application servers. Requests to the gateway are routed to the first available server in the list. If this server is not available, the gateway re-routes the request to the next available server. And so on.
Notice that the status of the primary Cognos application server for each Cognos gateway is monitored by the gateway itself; requests will be routed back to the primary server as soon as it returns to service.
Alternative: Cognos application server as gateway
Users who don't require gateway support for other C/C++ applications may elect to replace the Cognos gateways (mentioned in the previous section) with Cognos application servers with all services disabled (Figure 2):
Figure 2. Using the Cognos application server as a gateway
The topology shown in Figure 2 eliminates the need to manage and maintain the configuration between the gateways and the application servers. That configuration is managed by the auto-service discovery feature provided by the Cognos application server.
Cognos Content Manager in active and standby modes
The failover support of Cognos Content Manager allows multiple installations of Cognos Content Manager onto the Cognos solution. Select one of the installations as the active Cognos Content Manager and all other installations will be run in standby mode (Figure 3).
Figure 3. Cognos Content Manager in active and standby modes
If the active Cognos Content Manager fails, the Cognos application server can no longer communicate with it. In this situation, the Cognos application server will select a standby Cognos Content Manager, which becomes the new active Content Manager. All requests will then be directed to this newly active Content Manager. All other installations of Cognos Content Manager remain in standby mode for continuing failover support.
At least one active and one standby Cognos Content Manager should be installed for failover protection. The administrator should also aware that when the active Content Manager fails, unsaved session data is lost and users will be prompted to logon again after the new Content Manager becomes active.
IBM DB2 High Availability and Disaster Recovery (HADR)
The DB2-HADR is an easy-to-use feature of IBM DB2; it provides a high availability solution to handle different types of repository database failures of your Cognos solution. In the DB2-HADR environment, the administrator needs to set up two DB2 databases, one primary and one standby. Transaction logs are synchronized from the primary database to the standby database automatically (Figure 4).
Figure 4. IBM DB2 High Availability and Disaster Recovery (HADR)
In the DB2-HADR environment, connections from client to databases are managed by the automated client routing (ACR) settings. In normal circumstances, all requests are routed to the primary database. In the event of primary database failure, the client will receive a connection failure and will attempt to connect to the standby system automatically using the information stored in the ACR settings.
The DB2-HADR environment offers several choices of synchronization modes for balancing performance, scalability, and reliability of the system which should be considered by the Cognos administrator:
- Synchronous: No possible loss of data between primary and standby databases, but occurs at a cost of performance on the primary.
- Near Synchronous: Remote possibility of data lost if both primary database and standby database fail simultaneously, this mode is the best compromise of performance and reliability.
- Asynchronous: Best performing option but with potential data lost in the event of a failure of the primary or standby instance or of the connecting network.
We recommend that the Near Synchronous mode be set up for all Cognos solutions and Synchronous mode for mission-critical situations.
We hope these best practices will help you understand some of the system configurations available to provide high availability when delivering the Cognos power of smart business analytics on the IBM Cloud.
Look for more information on running Cognos on the cloud at the Cognos site and on developerWorks (Resources).
- For more in this series, see "Moving from a single- to a multiple-image topology" and "Sizing the architecture for performance and scalability."
- Find more information about Cognos Business Analytics.
- Check out other IBM Business Analytics software.
- The Cognos Proven Practices team delivers documentation of best practices built from real-life customer experiences.
- The Redbooks draft "IBM Smart Analytics Cloud" details a lab implementation of a smart analytics cloud.
- In the developerWorks cloud developer resources, discover and share knowledge and experience of application and services developers building their projects for cloud deployment.
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