The following table lists the impact on NFRs of the active/passive solution pattern:
|
NFRs |
Description |
|
Availability |
Availability of the system is improved due to the presence of a redundant element that can take over in the event that an active element fails or has to be taken out of service for maintenance. |
|
Performance |
There will be a minuscule (possibly insignificant) negative impact on performance due to the introduction of the 'failover' mechanism that switches in the redundant element should the active one fail. |
|
Scalability |
Not affected. |
|
Security |
Security may be negatively impacted by the additional element and failover mechanism, both of which have to be secured. |
|
Manageability |
Manageability is negatively impacted as part has been replaced by two and the failover mechanism also has to be managed. |
|
Maintainability |
Not affected. |
|
Flexibility |
Not affected. |
|
Portability |
Not affected. |
|
Cost |
The impact on cost can be significant: where there was a single element, there are now two (plus the cost of implementing the failover mechanism). If the elements are identical, we have basically doubled the cost of introducing that element. We can mitigate this by introducing a cheaper version of the element as the redundant one, but this restricts our implementation choices: we would definitely want to switch back to the active element as soon as it is introduced back into service. |