Chapter 2
Introduction to Flipt: Architecture and Capabilities
Step behind the curtain of Flipt and discover what sets this open-source feature flag platform apart as a lynchpin for modern software delivery. In this chapter, we demystify Flipt's architecture, deep-dive into its extensibility, and illuminate the powerful ecosystem that surrounds it. Whether you want hands-on operational fluency or architectural mastery, this guided tour reveals the inner workings, scalability, and integrations that make Flipt the choice for high-stakes engineering teams.
2.1 Flipt Architectural Overview
Flipt's architecture is anchored in a deliberate philosophy designed to reconcile the challenges of high availability, maintainability, and global scalability. Its defining characteristics are a stateless core, modular persistence layers, and a decoupled processing model. Each of these elements contributes to both operational robustness and extensibility, warranting a detailed examination of their design rationale and implications.
At the heart of Flipt lies a stateless core, a strategic choice that abstracts the system's business logic from mutable state. This core acts purely as a processor of input data and configurational rules, issuing decisions without retaining session-specific or intermediate data internally. By decoupling state from logic, Flipt achieves three distinct advantages:
- It facilitates horizontal scaling since instances can be dynamically added or removed with no synchronization overhead.
- It enables straightforward failover and recovery processes, as any core node can resume processing without state reconstruction.
- It simplifies the deployment model, permitting continuous delivery practices with minimal disruption.
This statelessness, however, necessitates robust external mechanisms for state management. Flipt addresses this through modular persistence options designed as interchangeable backend modules. These persistence layers are responsible for storing configuration states, feature flags, and metadata critical to Flipt's operation. The modular interfaces allow deployment teams to utilize a variety of storage systems-ranging from SQL databases, NoSQL stores, to distributed key-value systems-tailored to their infrastructure requirements. This tactical modularity confers operational flexibility without compromising the core processing logic. Notably, consistent API abstractions across persistence modules ensure that enhancements or swaps at the data layer do not propagate complexity or coupling into the core.
The modular persistence approach, however, introduces trade-offs, chiefly in consistency and latency. Different storage systems inherently provide varying consistency guarantees: strongly consistent stores may impede latency-sensitive operations, while eventually consistent ones can introduce stale reads. Flipt's design accommodates this spectrum by allowing configuration of consistency levels aligned with the deployment's availability and responsiveness needs, forming the basis of customized service-level objectives.
Complementing the stateless core and modular persistence is Flipt's decoupled processing model. This design separates configuration ingestion and state mutation from decision serving, effectively splitting the control and data planes. Configuration updates to feature flags and rules are ingested asynchronously, propagated through internal pipelines, and materialized in persistence layers without immediate coupling to real-time decision logic. Decision requests-queries to determine feature flag states for particular contexts-are handled independently, querying the persisted configuration data. This separation greatly enhances throughput and responsiveness in decision serving, as it avoids blocking on write operations or update propagation latencies.
Decoupling also improves system observability and operational control. Metrics and logs can be collected independently for ingestion pipelines and decision endpoints, allowing pinpoint diagnostics and targeted scaling. Moreover, through well-defined API contracts between planes, Flipt supports extensibility via plug-in components for validation, auditing, and canary releases without entangling the critical decision path.
These architectural choices cumulatively yield a system resilient to partial failures. Stateless cores can fail and restart without loss, while persistence modules can be replicated or replaced transparently. The asynchronous processing model allows graceful degradation where reads can proceed with last-known configurations even if writes are temporarily stalled. Consequently, Flipt is able to sustain high availability in globally distributed environments, accommodating intermittent network partitions and varying load patterns.
Maintainability gains stem from the modular separation and clean interfaces. Developers can iterate on data store implementations, decision algorithms, or ingestion mechanisms independently. Testing is simplified as modules can be mocked or isolated. Version upgrades can be phased by rolling out persistence modules or core logic separately, reducing risk.
In summary, Flipt's architecture embodies a synergy of statelessness, modularity, and decoupled processing to meet the demanding requirements of scalable feature management at global scale. Each core design decision trades off certain complexity or latency for gains in availability, extensibility, and maintainability. Understanding these trade-offs is essential when customizing, deploying, or extending Flipt in diverse operational contexts.
2.2 API Surface and Extension Points
Flipt exposes a rich and versatile API surface, designed to accommodate various integration needs through REST, gRPC, and GraphQL endpoints. This multiplicity provides flexibility for developers and systems architects to choose the most appropriate interaction protocol depending on their environment, technological stack, and performance requirements.
The REST API serves as the foundational interface, offering a straightforward HTTP-based mechanism for managing feature flags, retrieving flag evaluations, and administering configurations. Its statelessness and wide adoption make it an accessible option for external systems and scripting environments. The REST endpoints primarily follow resource-oriented design principles, with clearly defined URIs and HTTP verbs that correspond to CRUD operations, enabling intuitive interactions with flags, flag sets, segments, and more. Authentication is typically implemented via bearer tokens, emphasizing secure access control.
Complementing REST, the gRPC API provides a high-performance, strongly typed interface utilizing Protocol Buffers as its serialization format. The gRPC endpoints are optimized for low-latency and high-throughput scenarios, suitable for microservice ecosystems or backend platforms requiring efficient binary communication. This API supports bidirectional streaming, allowing real-time updates and continuous evaluations to be transmitted between clients and the Flipt server. The gRPC definitions encapsulate all major operational functionality available in REST but with added benefits such as contract versioning, advanced error handling, and tighter schema enforcement.
GraphQL presents a flexible query language that empowers clients to request exactly the data they need, minimizing over-fetching or under-fetching issues common in REST interactions. Flipt's GraphQL endpoint exposes a unified schema that bundles feature flags, evaluation results, targeting rules, and metadata into easily consumable entities. This facilitates complex queries that can traverse relationships between entities in a single request, simplifying client logic and improving performance in UI-driven or orchestrated environments.
Best practices for integrating with Flipt's APIs emphasize idempotency, robust error handling, and efficient data retrieval patterns. When performing flag evaluations, clients should cache results judiciously and leverage batching methods available in gRPC and GraphQL to reduce request overhead. When manipulating flag definitions or segments, it is recommended to adopt optimistic concurrency controls based on versioning metadata to prevent conflicting updates.
Automation and advanced workflows are significantly enhanced by Flipt's webhook support. Webhooks enable external systems to subscribe to state changes within Flipt-such as flag creation, modification, or deletion-and receive asynchronous HTTP callbacks. This mechanism allows orchestration pipelines, CI/CD processes, or notification systems to respond immediately to feature flag lifecycle events. Payloads sent to webhooks are structured with detailed context and change information, supporting flexible processing by subscribers. Best practices include verifying webhook request signatures to ensure security, implementing retry policies for reliability, and using event filtering to narrow down the scope of received notifications.
Extensibility is realized through Flipt's robust plugin architecture, which provides extension points for custom logic, integrations, and workflows. Plugins can be developed to augment evaluation semantics, inject...
