service-decomposition

Strangler Fig: Routing Between Monolith and Microservice via Feature Flag

You are extracting a feature from a monolith into a microservice, but you cannot switch all traffic at once. This workflow checks a feature flag to decide the routing target, then uses a SWITCH to send the request to either the monolith or the new microservice, and optionally compares the results to validate equivalence.

Workflow

feature, request
       |
       v
+---------------------------+
| sd_check_feature_flag     |   target: "monolith", percentage: 100
+---------------------------+
       |
       v
  SWITCH on target
  +--"monolith"------------------+--"microservice"--+
  | sd_call_monolith             | sd_call_micro... |
  | source: "monolith"          | source: "micro."|
  | result: "processed"         | result: "proc."|
  +------------------------------+-----------------+
       |
       v
  sd_compare_results (optional)   match: true

Workers

CheckFeatureFlagWorker -- Checks feature flag. Currently routes to target: "monolith" at percentage: 100.

CallMonolithWorker -- Processes in the legacy system. Returns source: "monolith", result: "processed".

CallMicroserviceWorker -- Processes in the new service. Returns source: "microservice", result: "processed".

CompareResultsWorker -- Compares monolith and microservice results. Returns match: true.

Tests

No unit tests for this example.

Running

See ../../RUNNING.md for setup and execution instructions.