Dynamic Routing

By default, bridgeTransform takes a parsed .bridge file and attaches it to your schema statically. But for enterprise gateways, multi-tenant SaaS, and strict compliance environments, a static graph isn’t enough.

The Bridge supports Context-Aware Topology Switching. Instead of passing a static array of instructions, you can pass a router function: (context: any) => Instruction[].

This function is evaluated per-request, allowing you to hot-swap the entire physical wiring of your GraphQL API based on the user’s identity, region, or billing tier—without writing a single if/else statement in your business logic.

How it works

When a request hits your GraphQL server, the engine passes the GraphQL context to your router function. The function returns the specific .bridge AST that should execute for that exact request.

import { bridgeTransform, parseBridge } from "@stackables/bridge";

// 1. Parse your different topologies at startup
const euBridge = parseBridge(fs.readFileSync("eu-infrastructure.bridge"));
const usBridge = parseBridge(fs.readFileSync("us-infrastructure.bridge"));

// 2. Define the dynamic router
const schema = bridgeTransform(baseSchema, (context) => {
  // Read the user's region from the request context
  if (context.user.region === "EU") {
    return euBridge;
  }
  return usBridge;
});

Why use Dynamic Routing?

By keeping the routing logic in the host server and the data mapping in the .bridge files, you achieve a perfect separation of concerns between Platform Engineering and Product Development.

1. Data Sovereignty & Compliance (GDPR)

Ensure EU users never accidentally touch US servers. If the context dictates the EU bridge, the US endpoints physically do not exist in the execution graph for that request. It is mathematically impossible for data to leak to the wrong region.

2. Tiered SLAs (Free vs. Pro)

Swap expensive tools for cheap ones based on billing.

const schema = bridgeTransform(baseSchema, (context) => {
  // Pro users get real-time GPT-4; Free users get a cached/smaller model
  return context.user.plan === "PRO" ? premiumBridge : budgetBridge;
});

3. Canary Releases & A/B Testing

Safely migrate between external API providers (e.g., swapping SendGrid for Postmark) by routing a small percentage of traffic to the new topology.

const schema = bridgeTransform(baseSchema, (context) => {
  // Route 5% of traffic to the experimental v2 pipeline
  return Math.random() < 0.05 ? experimentalBridge : stableBridge;
});

Security Note

Because .bridge files are parsed into serializable ASTs (Instruction[]), the router function is incredibly fast. Evaluating the context and returning an in-memory AST array adds virtually zero latency to your request pipeline, making it ideal for high-throughput edge gateways.