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Merge pull request #3 from barbacane-dev/add-multi-spec-blog-post
Add blog post: One Gateway, Many Specs
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‎src/content/blog/one-gateway-many-specs.md‎

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---
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title: "One Gateway, Many Specs: How Barbacane Unifies Your API Ecosystem"
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description: "Most API tooling assumes one repo, one spec. But microservices don't work that way. Explore how Barbacane's multi-spec compilation merges your OpenAPI and AsyncAPI files into a single, validated artifact."
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publishDate: 2026-02-13
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author: "Nicolas Dreno"
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tags: ["barbacane", "api-gateway", "openapi", "asyncapi", "microservices"]
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---
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*Most API tooling assumes one repository, one specification. But your architecture doesn't work that way.*
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In our [previous article](/blog/beyond-configuration-drift/), we explored how Barbacane eliminates configuration drift by compiling your OpenAPI spec directly into the gateway's runtime artifact. One spec, one `.bca` file, zero drift.
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But what happens when your architecture has more than one spec?
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---
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### The Multi-Spec Reality
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In a typical microservices setup, your API surface isn't described by a single file. Whether you're working contract-first or generating specs from code, you end up with multiple specifications:
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- A **User Service** with its own `openapi.yaml`
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- An **Order Service** with its own `openapi.yaml`
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- An **Inventory Service** exposing both REST endpoints and event consumers, described across OpenAPI and AsyncAPI files
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- Event schemas scattered across repos
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Each file is validated in isolation, deployed independently, and versioned on its own timeline. Single-spec tools can't see across these boundaries, so cross-service mismatches only surface at runtime. The feedback loop is as slow as it gets: write specs, deploy, discover the conflict in production, fix, redeploy.
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---
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### One Command, Multiple Specs
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Barbacane's `compile` command accepts multiple specification files in a single invocation:
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```bash
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barbacane compile \
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-s services/user-service/openapi.yaml \
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-s services/order-service/openapi.yaml \
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-s services/inventory-service/openapi.yaml \
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-s services/inventory-service/asyncapi.yaml \
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-m barbacane.yaml \
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-o gateway.bca
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```
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The compiler parses every file (OpenAPI 3.x and AsyncAPI 3.0.x) and merges their routes into a single `.bca` artifact. The output message tells you exactly what you got:
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```
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compiled 4 spec(s) to gateway.bca (23 routes, 5 plugin(s) bundled)
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```
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One artifact. One routing table. One deployment.
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---
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### What Multi-Spec Compilation Actually Does
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When you pass multiple specs, the compiler:
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1. **Parses each file independently.** OpenAPI and AsyncAPI specs are each validated against their respective standards.
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2. **Merges routes into a unified routing table.** All operations from all specs end up in a single `routes.json` inside the `.bca` artifact. The gateway doesn't care which file a route came from; it serves them all.
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3. **Detects routing conflicts.** If two specs define the same path and method combination (e.g., both declare `GET /users/{id}`), compilation fails with error `E1010`. This is a hard gate: you cannot produce an artifact with ambiguous routing.
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4. **Bundles everything together.** WASM plugins, dispatcher configurations, and the original source specs are all packaged into the artifact. The source specs remain accessible at `/__barbacane/specs` for documentation and debugging.
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This isn't magic. It's the same compilation pipeline applied across multiple input files. But the practical impact is a meaningful **shift left**: routing conflicts that would previously surface as mysterious 404s or wrong-handler bugs in production now fail your build.
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---
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### Specs Stay Accessible at Runtime
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Compilation merges routes, but the original source specs aren't thrown away. They're embedded in the `.bca` artifact and served by the gateway at `/__barbacane/specs`:
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```
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GET /__barbacane/specs
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```
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This returns an index of every spec that was compiled into the running artifact, with links to the full OpenAPI and AsyncAPI documents. The served specs are stripped of Barbacane-specific extensions (`x-barbacane-*`), so what your API consumers and documentation tools see is clean, standard OpenAPI and AsyncAPI with no vendor-specific noise. And because these are the exact specs that were compiled, they can't drift from what the gateway is actually running.
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No separate spec hosting. No stale docs. The gateway *is* the documentation server.
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---
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### A Practical Example
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Consider an e-commerce platform with four services:
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```
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User Service → openapi.yaml
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Order Service → openapi.yaml
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Inventory Service → openapi.yaml + asyncapi.yaml
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Notification Svc → asyncapi.yaml
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```
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Without multi-spec compilation, you'd deploy each service's gateway configuration independently, trusting that teams coordinated their path prefixes and schema versions. With Barbacane:
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```bash
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barbacane compile \
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-s services/user-service/openapi.yaml \
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-s services/order-service/openapi.yaml \
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-s services/inventory-service/openapi.yaml \
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-s services/inventory-service/asyncapi.yaml \
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-s services/notification-service/asyncapi.yaml \
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-m barbacane.yaml \
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-o gateway.bca
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```
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If the Order Service accidentally defines a route that collides with the User Service, compilation fails. You find out in seconds, not after a deploy.
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---
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### CI/CD Integration
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Multi-spec compilation fits naturally into a CI gate. Block merges to `main` if the combined specs don't compile cleanly:
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```yaml
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# .github/workflows/validate-contracts.yml
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jobs:
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validate:
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runs-on: ubuntu-latest
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steps:
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- uses: actions/checkout@v4
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- name: Compile gateway artifact
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run: |
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barbacane compile \
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-s services/user-service/openapi.yaml \
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-s services/order-service/openapi.yaml \
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-s services/inventory-service/openapi.yaml \
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-s services/inventory-service/asyncapi.yaml \
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-m barbacane.yaml \
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-o gateway.bca
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```
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A non-zero exit code (1 for validation failures, 2 for manifest errors) blocks the pipeline. No ambiguous warnings: either the specs compile together, or they don't.
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---
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### Progressive Adoption
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You don't have to compile everything at once. Start with your most critical services and expand:
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```bash
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# Start with two services
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barbacane compile \
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-s user-service/openapi.yaml \
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-s auth-service/openapi.yaml \
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-m barbacane.yaml \
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-o gateway.bca
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# Later, add event-driven services
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barbacane compile \
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-s user-service/openapi.yaml \
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-s auth-service/openapi.yaml \
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-s order-service/openapi.yaml \
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-s order-service/asyncapi.yaml \
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-m barbacane.yaml \
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-o gateway.bca
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```
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Each additional spec increases the surface area of conflict detection. The more specs you compile together, the more mismatches you catch before deployment.
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---
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### Strengths and Limitations
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Multi-spec compilation extends the "compile, don't configure" philosophy across service boundaries, but it's worth understanding what it does and doesn't do today.
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**What it catches:**
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- Routing conflicts (duplicate path + method across specs)
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- Spec-level validation errors (malformed OpenAPI/AsyncAPI)
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- Missing plugin or dispatcher declarations
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**What it doesn't do (yet):**
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- Cross-spec schema validation (e.g., verifying that an `Order` object is consistent between two specs)
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- Breaking change detection between spec versions
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- Dependency graph analysis between services
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These are real limitations. Multi-spec compilation today is primarily about *route-level unification and conflict detection*, not deep semantic analysis across your API ecosystem. For schema consistency, you'll still need complementary tooling or careful code review.
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---
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### Shifting Left Across Service Boundaries
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The idea behind "shift left" is simple: catch problems earlier in the development lifecycle, when they're cheapest to fix. Linters shift left on code quality. Type systems shift left on correctness. Multi-spec compilation shifts left on *cross-service integration*.
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In our [previous article](/blog/beyond-configuration-drift/), we showed how Barbacane shifts gateway configuration left by compiling the spec into the runtime artifact. Multi-spec compilation takes this further: instead of discovering that two services disagree on routing after deployment, you discover it at compile time, in CI, on a pull request.
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It's not a silver bullet. Cross-service consistency is a hard problem, and route-level conflict detection is just one piece of the puzzle. But it's a piece that most gateway tooling doesn't offer at all, and one that pays off immediately in any multi-service architecture. The earlier you catch a conflict, the less it costs.
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---
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*Barbacane is open source (Apache 2.0) and available at [github.com/barbacane-dev/barbacane](https://github.com/barbacane-dev/barbacane). Check the [documentation](https://docs.barbacane.dev/) for the full CLI reference and getting started guide.*

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