Implementing High Availability, Failover, and Load Management

High availability, failover, and load management can be implemented at several components:

There are two main types of schemes to support high availability, failover, and load management schemes:

In the following sections we will take a look at how these schemes can be implemented with WebFOCUS for the components listed earlier.

Hardware and Software

The following images illustrate how hardware can be configured to support the commonly used Active-Active load management schemes to support the clustered architecture models covered in Designing the WebFOCUS 8 Architecture.

We make reference to the Presentation Layer, which is comprised of the WebFOCUS Client and ReportCaster, and the Reporting and Metadata Layer, which is comprised of the Reporting Server.

This section is not intended to cover high availability and failover at the WebFOCUS Application Level. Later on we will cover how WebFOCUS Workload Distribution Facility (CLM) can be used to provide high availability and failover at the WebFOCUS Application Level.

Note: Third-party resources that are required to support the clustered architecture models must also support high-availability.

In the following Active-Active Single-Tier Clustered Architecture Model image:

There are two machines, both in active mode.
Each machine hosts both the Presentation and Reporting and Metadata Layers.
Provides high availability and failover at the machine level.
- For active machines:
  - Both machines are actively listening for incoming requests and will process all requests concurrently.
  - If one of the machines become unavailable, all requests will be routed to the remaining machine.

In the following Active-Active Multi-Tier Clustered Architecture Model image:

There are two machines, each hosting the Presentation Layer.
There are three machines, each hosting the Reporting and Metadata Layer.
Provides high availability and failover at the machine level for both Presentation and Reporting and Metadata Layers.
- Presentation Layer. Active machines. Both machines are actively listening for incoming requests and will process all requests concurrently.
- Reporting and Metadata Layer. Active machines. All requests will be routed to all three machines, each of which are actively listening for incoming requests and will process all requests concurrently.

Maintaining Performance When Cluster Members Become Unavailable

There must be adequate resources to support desired load in the event one or more cluster members become unavailable. Companies must establish policy as to what constitutes acceptable degradation.

For example, if you have a cluster of two Reporting Servers running at 75% capacity, and one goes offline, the workload of the remaining Reporting Server will be increased potentially resulting in performance degradation. To maintain the same performance of the system as when running at full capacity, consider increasing the capacity of the remaining Reporting Server or adding a third Reporting Server node.

Considerations for Web Servers and Java Application Servers

Web server farms can be fronted by load balancers to support load management and failover schemes, as shown in the following image.

In the Failover/Load Management image, a load balancer routes user requests to the web servers in the web server farm using a defined dispatch algorithm. Each web server in the Web Server Farm is installed with a web server plug-in to communicate to the application servers in the Application Server Farm that are hosting WebFOCUS. The web server plug-in has a default dispatch algorithm.

There are special considerations for web servers and application servers, which are described below.

Fronting the Application Server With a Web Server

Often, we are asked, "Do we need a web server and an application server?" While WebFOCUS will work with both a web server and application server, or only an application server that has a built-in HTTP server, it is best to design an architecture using web servers working in tandem with application servers for WebFOCUS usage.

A web server primarily serves up static and dynamic pages from HTTP requests. It does not support transactions, database connection pooling, servlet, or JavaServer™ Pages (JSP) files, and will typically pass such requests to a server-side program that can handle it, such as a servlet container. WebFOCUS consists of web applications that are comprised of related files, including HTML files, JavaServer Pages files, and servlets.

Some of the advantages in fronting a application server with a web server are outlined below:

Content. Separate content, in that you can have the web server serve up static pages and images so that some of the burden on the application server is reduced.
Scalability. By placing a web server in front of the application server, you can use the load balancing features of the web server and plug-ins to distribute the workload among several application servers.
Security. Placing a web server in front of the application server provides an additional level of filtering and security that can be integrated with SSO policy agents of security authentication providers, such as CA SiteMinder.

WebFOCUS

In this section:

Customers can leverage the built-in failover and load management capabilities of WebFOCUS to minimize application downtime and distribute workload to maintain optimal performance. These capabilities are implemented for the following WebFOCUS components.

Workload Distribution Facility. The Cluster Manager (CLM) works in tandem with the Presentation Layer to distribute workload across a cluster of WebFOCUS Reporting Servers.
ReportCaster Workload Distribution. The Workload Manager distributes scheduled jobs across a cluster of Distribution workers.

Let us first take a look at how these components are designed to work and how they can be best used to satisfy failover and workload distribution requirements using supported load-management schemes.

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Workload Distribution Facility

The Workload Distribution Facility (CLM) is an independent server component that manages one or more clusters of WebFOCUS Reporting Servers. You can have one CLM or a cluster of CLMs running at the same time in Active-Active mode. To leverage CLM, you need to configure the Presentation Layer to communicate to one or a cluster of CLMs. It is recommended to use a cluster of CLMs for high availability and failover.

The main functions of the CLM are to:

Use collected polling statistics to determine which remote WebFOCUS Reporting Servers a WebFOCUS request should be routed. CLM sends this information to the Presentation Layer, which will forward the user request to the recommended server.
Maintain attributes for each remote WebFOCUS Reporting Server.
Monitor all of the remote WebFOCUS Reporting Servers through a central console.
Define rules for monitoring and dispatching requests to the remote WebFOCUS Reporting Servers.
Log statistics about remote WebFOCUS Reporting Servers for reporting and subsequent analysis.

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Workflow for CLM Processing

When a user submits a request to the Presentation Layer, the high-level workflow for processing that request is outlined, as shown in the following image.

Request is submitted and routed through the load balancer to a web server.
Request is sent from the web server to the application server, where the WebFOCUS Client or ReportCaster is installed.
WebFOCUS Client or ReportCaster asks CLM for the remote WebFOCUS Reporting Server to which the request should be sent.
CLM uses collected polling statistics to determine the most appropriate remote WebFOCUS Reporting Server to process the request, and notifies the WebFOCUS Client or ReportCaster.
The WebFOCUS Client or ReportCaster sends the request to the specified WebFOCUS Reporting Server.

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ReportCaster Workload Distribution

When ReportCaster is configured for Workload Distribution, the Workload Manager is activated on the ReportCaster Distribution Server. The Workload Manager distributes scheduled jobs to a cluster of Workers for processing. This provides a scalable way to process a larger number of scheduled jobs. CLM and ReportCaster Workload Distribution can be configured to work in tandem to manage the workload.

Note: ReportCaster supports Active-Passive failover for the ReportCaster Distribution Servers. There can only be a single Primary ReportCaster Distribution Server in a WebFOCUS instance. If the Primary ReportCaster Distribution Server becomes unavailable, then the roles are switched and the Failover ReportCaster Distribution Server is automatically brought online and becomes the Primary ReportCaster Distribution Server. ReportCaster supports Active-Active failover and load management for the Workload Distribution Workers.

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Configuring WebFOCUS for High Availability, Failover, and Load Management

The following is the recommended order for configuring WebFOCUS to support high availability, failover, and load management.

WebFOCUS Reporting Servers.
Cluster JSCOM agents under Java Services.
Create Data Services on each WebFOCUS Reporting Server.

Workload Distribution Facility (CLM)

Install a cluster of CLMs. For each installation of the Workload Distribution Facility (CLM):
- Enable the Cluster Manager (CLM).
- Assign values to CLM properties.
- Add Active Remote Server nodes and assign values for Remote Server properties.
- Create a CLUSTER node called EDASERVE and assign values for Remote Server properties.
- Create additional CLUSTER nodes if the configuration requires multiple clusters and assign values for Remote Server properties.
- Assign Remote Servers to each of the CLUSTER nodes.

WebFOCUS Client

Create CLM Processing nodes to match the CLM CLUSTER nodes created on the CLM. The WebFOCUS Client has to be configured to communicate to one or more clusters defined on the CLM.
Convert the default Client node, EDASERVE, to be a CLM Processing node.
Create a separate CLM Processing node for each additional CLM CLUSTER node, using identical names. For example, if the CLM CLUSTER node is called UNIXCLUS, then the name of the CLM Processing node must also be UNIXCLUS. Assign values for properties.
If using a cluster of CLMs, add each CLM to the CLM Processing node using the Add option.

ReportCaster

As of WebFOCUS Release 8.1 Version 03, ReportCaster leverages the WebFOCUS Client communications file, odin.cfg. You no longer have to create Data Servers in the ReportCaster configuration GUI. Instead, when you click New from the ReportCaster configuration GUI, the list of Client, CLM Processing, and Cluster nodes defined on the WebFOCUS Client will display. You can then choose the appropriate nodes that are required for ReportCaster scheduling.

The recommendation is to select all listed nodes because at the time when the schedule is being created, a check is not done to ensure that the assigned server for the resource being scheduled is available to ReportCaster. If the assigned server is not available to the Primary ReportCaster Distribution Server, the scheduled job will fail when it is executed. This capability is being evaluated for a future release.