Availability Guide for Application Design

Instrumenting an Application for Availability
Availability Guide for Application Design—525637-004
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Alternatives to DSM
You can find more information about automating object management using HP’s
implementation of SNMP in the SNMP Manager Programmer’s Guide and SNMP
Subagent Programmer’s Guide. You can find a full description of DSM in the
Distributed Systems Management (DSM) Manual; the following subsections discuss
the use of DSM to instrument applications so that they can be managed as objects.
Alternatives to DSM
Applications that are not managed through the DSM architecture can be designed with
various response levels to problems that threaten the availability of the application.
Historically, such approaches have included:
•
Provide no support at all.
When an application encounters a problem, it simply stops without telling anyone.
It could take a long time before the operations staff is aware that a problem exists.
•
Inform the end user.
When an application encounters a problem it sends a message to the end user.
Here, the end user is probably not trained to understand or respond to the
problem. In addition, such messages are likely to be missed or ignored if they
appear among lots of regular application output.
•
Notify the operators of every event.
When an application encounters a problem, it sends a message to the operator's
console. Here, a suitably trained person receives the information. However, critical
messages can easily be lost among screens full of general status information.
Moreover, the time it takes an operator to analyze and resolve the problem and
implement the solution can still lead to significant downtime of the application.
•
Code for all contingencies.
When an application encounters a problem, it invokes processes or calls on
procedures within itself to resolve the problem. This approach works well and is
recommended for all anticipated error conditions that the application is capable of
recovering from by itself. However, this approach offers no solution for errors from
which the application is not capable of recovering without help, nor does it provide
help when an unexpected error condition occurs.
Clearly, all these approaches have significant drawbacks for managing problems.
Advantages of DSM
Appropriate use of the DSM architecture can greatly enhance the availability of your
application by monitoring events generated by your application or by HP subsystems,
and by facilitating responses to those events through command and control interfaces.
Because operational outages are often the most common cause of application
downtime, DSM can further enhance the availability of an application by:
•
Providing consistent interfaces across various subsystems and applications