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Web Server fail-over Proven Practice Product(s): IBM Cognos 8

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Web Server fail-over Proven Practice Product(s): IBM Cognos 8
Proven Practice
Web Server fail-over
Product(s): IBM Cognos 8
Area of Interest: Infrastructure
Web Server fail-over
2
Copyright
Copyright © 2008 Cognos ULC (formerly Cognos Incorporated). Cognos ULC
is an IBM Company. While every attempt has been made to ensure that the
information in this document is accurate and complete, some typographical
errors or technical inaccuracies may exist. Cognos does not accept
responsibility for any kind of loss resulting from the use of information
contained in this document. This document shows the publication date. The
information contained in this document is subject to change without notice.
Any improvements or changes to the information contained in this document
will be documented in subsequent editions. This document contains
proprietary information of Cognos. All rights are reserved. No part of this
document may be copied, photocopied, reproduced, stored in a retrieval
system, transmitted in any form or by any means, or translated into another
language without the prior written consent of Cognos. Cognos and the
Cognos logo are trademarks of Cognos ULC (formerly Cognos Incorporated)
in the United States and/or other countries. IBM and the IBM logo are
trademarks of International Business Machines Corporation in the United
States, or other countries, or both. All other names are trademarks or
registered trademarks of their respective companies. Information about
Cognos products can be found at www.cognos.com
This document is maintained by the Best Practices, Product and Technology
team. You can send comments, suggestions, and additions to
[email protected] .
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Contents
1
1.1
2
2.1
2.2
2.3
2.4
2.4.1
2.4.2
Introduction ......................................................................................................4
Purpose ............................................................................................................4
The IBM Cognos 8 Gateway ................................................................................5
The Web Tier ....................................................................................................5
Performance Scaling in the Application Tier ..........................................................5
Application Tier Failover .....................................................................................6
Designing for Web Tier failover ...........................................................................6
Manual change over...........................................................................................6
Automatic Failover .............................................................................................8
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1
Introduction
1.1
Purpose
When designing a IBM Cognos 8 implementation, consideration must be paid
as to how important high availability is. For example, a system that prints
marketing correspondence as scheduled batch jobs can probably afford to be
off-line for a number of hours without unduly affecting business operations.
Conversely, an on-line reporting system used by call centre staff to call up
customer records while speaking with clients will require high availability.
Every tier within a IBM Cognos 8 environment has the potential to be the
point of failure for the system – accordingly each tier has strategies to enable
operation to continue should a single component fail. This document is an
overview to providing fail over capabilities for the web server(s) used to
access IBM Cognos 8.
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2
The IBM Cognos 8 Gateway
2.1
The Web Tier
The IBM Cognos 8 Gateway operates within the Web Tier of the Application
stack. Installing the Gateway component on a Web Server machine provides
the native code executed by the Web Server to allow communication with the
IBM Cognos 8 Dispatchers (in the Application tier) along with static web page
content utilized by the IBM Cognos 8 Portal and Studio interfaces. The
amount of processing power required by the Gateway is many times smaller
than that of the Application Tier components for any given IBM Cognos 8
request. The static content is handled by the web server itself (Apache, IIS
etc. – the same web servers that service millions of hits a day on many
Internet sites) and the dynamic content is simply being passed through. The
‘heavy lifting’ takes place in the Application and Data Tiers – the majority of
the time the Gateway will be waiting for these components to complete their
tasks. Even if the Web Server is being used to handle authentication
information, you can expect a single, correctly tuned web server can handle
all the requests that a substantial IBM Cognos 8 installation would generate
without any issues.
2.2
Performance Scaling in the Application Tier
Because it is rarely the Gateway / Web Server that is the performance
bottleneck in a IBM Cognos 8 environment, for load-balancing and scalability
purposes it is usually the Application tier that has additional hardware added
to it. Performance wise, this is entirely logical. When configuring the
Gateway, a list of Dispatchers that can handle the request is specified. By
adding additional Application tier resources, the Gateway should be serviced
quicker, which in turn can respond to the users faster.
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2.3
6
Application Tier Failover
Adding additional servers to the Application tier does not only provide
performance benefits. Intentionally or unintentionally, the additional
hardware also adds an element of failover. By specifying multiple
Dispatchers that can service the Gateway, we are not only adding for
performance, but indicating that there is more than one resource available to
execute a request. If one the Dispatchers should become unavailable, then
the Gateway will simply use the others in the list.
Having failover support in the Application tier is certainly desirable, but unless
the rest of the system is designed accordingly, there will still be potential
single point of failures, one of which is the Web tier.
2.4
Designing for Web Tier failover
A IBM Cognos 8 install can accommodate multiple gateways, which although
not solely for the benefit of failover, allows redundancy to be created in the
Web tier.
2.4.1
Manual change over
At the simplest level, this could be two separate web servers with the IBM
Cognos 8 gateway installed. Should one of the web server fails, users could
switch from server1 to server2.
Users
http://server1/cognos8
http://server2/cognos8
Web Tier
Application Tier
Data Tier
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Although this does work, it clearly isn’t ideal, as it relies on the users
remembering that there are additional web servers available and manually
changing the URL they hit.
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Web Server fail-over
2.4.2
8
Automatic Failover
A more practical (and common) solution is to place a hardware router in front
of the web servers. Users then hit this router which load-balances between
the two (or more) web servers that run the IBM Cognos 8 gateway. In
addition to load balancing traffic, the router regularly checks that each web
server is responding – should a one of web servers fail to respond, then the
router stops passing traffic to it (usually for a preset amount of time, before
checking it again).
To the users, any fail-over should be seamless. They will always access a
consistent URL (the router), whichever web server actually ends up
processing the request.
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