Choosing Inner source
Choosing to use inner source for your product should be a deliberate and conscious decision based on its benefits. Flutter is a group of independent divisions so from a group perspective there are three high-level patterns for product development:
- Independent : designed, built/bought and operated independently within a division by their teams with no cross-divisional collaboration.
- Delegated : designed, built/bought and operated by one division on behalf of all other divisions.
- Inner Source : designed and built collaboratively by several divisions, with each division operating their own deployment.
Comparing these approaches from the perspective of a division:
|Predictability||Velocity and priorities fully controlled.||Projects depend on an external prioritisation process with other divisions.||Velocity and priorities controlled, but intent must be agreed with other divisions and cycle time expectation adjusted.|
|Efficiency||Start from scratch. Need to implement all features.||All features are implemented by another division, just need to use.||Need to implement specific priorities and deployment, get most features from other divisions.|
|Quality||Aligned with our standards, and can trade-off quality for velocity as desired.||Aligned with another division's standards and treated as a service dependency.||Aligned with cross-divisionally agreed standards, limited ability to trade-off quality for velocity.|
|Stability||Operational concerns fully controlled.||Must be managed as an external service dependency.||Operational concerns fully controlled.|
Watch an 8 minute video introduction to choosing Inner Source and an explanation of the Inner Source pyramid from Rob.
Independent development is the default choice, and is optimum when:
- expected efficiency gain of re-use across divisions is low (e.g. front-end web or app interfaces).
- capability is important but not complex enough to justify cross-divisional collaboration (e.g. content management).
- cost of change from existing divisional capability is too great to consider alternatives (e.g. data services)
Delegated development is optimum when:
- capability is required but not strategically important (e.g. identity management, HR system).
- the commercial value of a capability is primarily realised in a single division (e.g. PokerStars).
- 3rd party integrations, dependencies or relationships are optimised by centralised management (e.g. casino games).
Inner Source development is optimum when:
- high complexity makes the value of re-use high, and capability is strategically important for many divisions (e.g. betting platform).
- divisional priorities for a capability are naturally complementary (e.g. sports modelling – where US, UK, Australia and International all prioritise different sports).
- cross-divisional consensus is necessary for an effective capability (e.g. inter-divisional network).
Inner Source Pyramid
Inner source at Flutter is described as a pyramid with various stages. This reflects the reality that there is no single inner source operating model – it depends on the capability needs & teams. Similarly, Independent and Delegated patterns are families of operating models and the boundaries between the development patterns are blurred.
- Readable Source on the Inner Source Pyramid can be Independent or Delegated capabilities that value development transparency (e.g. for community learning) or plan to accept contributions in future.
- Any Inner Source capability can be copied (“forked”) and changed into a new Independent capability to accelerate start-up.
- Guest Contribution capabilities are owned by a divisional host team, and if contribution stops over time can become Delegated.
- Some Inner Source capabilities that accept cross-divisional contribution still Delegate to a single division for a single managed deployment.
Both the inner source pyramid and the 3 development patterns are a simplification: but they provide a powerful language with which to discuss, inform and make decisions about the best way forward within the group for a specific capability.