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Software Architecture Guide

Flexibility

Explanation

Section titled “Explanation”

Flexibility describes how well a product can be adapted when requirements or contexts of use change. In ISO/IEC 25010:2023, Flexibility replaced Portability (see the article ISO/IEC 25010:2023 Product Quality Model Revision).

The standard lists four sub-characteristics:

  • Adaptability: adapting a product to, or moving it to, different hardware, software or other environments. Support staff, operations staff or end users can do this work. When end users do it, adaptability equals suitability for individualization.
  • Scalability: handling growing or shrinking workloads. Elasticity is a related quality.
  • Installability: the third child of Flexibility in the standard’s tree.
  • Replaceability: the ability to use other software products in place of the present one. This lowers lock-in risk, meaning the risk of being tied to one product.

Some constructs make change easier. Microservices are one example (see Microservices Architecture). Each microservice is a component that can be replaced and upgraded on its own. After a change, only the modified services need redeploying. Things that change together should stay together. If two services keep changing together, that suggests merging them. Moving code across service boundaries is hard.

Example

Section titled “Example”

A company runs an online shop as several small services. Holiday traffic grows, so the team adds capacity for the checkout service (scalability). The payment service needs a new provider. The team swaps that one service and redeploys only it (replaceability). The rest of the shop stays untouched.

Trade-offs

Section titled “Trade-offs”

Flexibility has a cost. Replaceability is not free and is rarely worth maximizing. Lock-in is the price of low replaceability, so a team should decide where it accepts lock-in. Microservices ease change, but moving code across service boundaries is hard.

Checks

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  • The document states which Flexibility sub-characteristics (adaptability, scalability, installability, replaceability) matter for the system.
  • Scalability requirements say whether the workload is expected to grow, shrink, or both.
  • Replaceability targets are stated, and accepted lock-in is named as a conscious choice.
  • The document says who performs adaptation: support staff, operations staff or end users.
Section titled “Related”

Sources

Section titled “Sources”