Configure Api Gateway

---
name: configure-api-gateway
description: >
  Deploy and configure an API gateway (Kong or Traefik) to handle API traffic management,
  authentication, rate limiting, request/response transformation, and routing. Covers plugin
  configuration, upstream services, consumer management, and integration with existing
  infrastructure. Use when multiple backend services need a unified API endpoint, when
  centralized authentication or rate limiting is required, when implementing API versioning,
  or when needing detailed analytics and load balancing for microservices.
license: MIT
allowed-tools: Read Write Edit Bash Grep Glob
metadata:
  author: Philipp Thoss
  version: "1.1"
  domain: devops
  complexity: intermediate
  language: multi
  tags: api-gateway, kong, traefik, rate-limiting, authentication, routing, middleware
---

# Configure API Gateway

Deploy and configure an API gateway for centralized API traffic management and policy enforcement.

## When to Use

- Multiple backend services need unified API endpoint with consistent policies
- Require centralized authentication/authorization for API access
- Need rate limiting and quota management across APIs
- Want to transform requests/responses without modifying backend services
- Implementing API versioning and deprecation strategies
- Need detailed API analytics and monitoring
- Require service discovery and load balancing for microservices

## Inputs

- **Required**: Kubernetes cluster or Docker environment
- **Required**: Choice of API gateway (Kong or Traefik)
- **Required**: Backend service endpoints to proxy
- **Optional**: Authentication provider (OAuth2, OIDC, API keys)
- **Optional**: Rate limiting requirements (requests per minute/hour)
- **Optional**: Custom middleware or plugin configurations
- **Optional**: TLS certificates for HTTPS endpoints — the gateway terminates TLS for every route behind it, so provision via cert-manager and verify auto-renewal is actually running; an expiry takes down all routes at once, not one

## Procedure

> See [Extended Examples](references/EXAMPLES.md) for complete configuration files and templates.
>
> Roll out incrementally in step order — do not enable all plugins/middleware in one sync; verify each step's **Expected** block before layering the next (routing → authentication → rate limiting → transformations → advanced features).

### Step 1: Install API Gateway

Deploy the API gateway with database (Kong) or file-based config (Traefik).

**For Kong with PostgreSQL:**
```yaml
# kong-deployment.yaml (excerpt - see EXAMPLES.md for complete file)
apiVersion: v1
kind: Namespace
metadata:
  name: kong
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: kong
  namespace: kong
spec:
  replicas: 2
  # ... (PostgreSQL, migrations, services - see EXAMPLES.md)
```

**For Traefik:**
```yaml
# traefik-deployment.yaml (excerpt - see EXAMPLES.md for complete file)
apiVersion: v1
kind: Namespace
metadata:
  name: traefik
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: traefik
  namespace: traefik
spec:
  replicas: 2
  # ... (RBAC, ConfigMap, services - see EXAMPLES.md)
```

See [EXAMPLES.md](references/EXAMPLES.md#step-1-install-api-gateway) for the complete deployment manifests

Deploy:
```bash
kubectl apply -f kong-deployment.yaml  # OR traefik-deployment.yaml
kubectl wait --for=condition=ready pod -l app=kong -n kong --timeout=300s
kubectl get svc -n kong kong-proxy  # Get load balancer IP
```

**Expected:** Gateway pods running with 2 replicas. Load balancer service has external IP assigned. Admin API accessible (Kong: port 8001, Traefik: dashboard port 8080). Health checks passing. CPU/memory requests and limits set on the gateway pods — a gateway that hits its CPU limit under load is throttled, and that surfaces as rising latency, not as errors or restarts.

**On failure:**
- Check pod logs: `kubectl logs -n kong -l app=kong`
- Verify database connection (Kong): `kubectl logs -n kong kong-migrations-<hash>`
- Check service account permissions (Traefik): `kubectl get clusterrolebinding traefik -o yaml`
- Ensure ports not already bound: `kubectl get svc --all-namespaces | grep 8000`

### Step 2: Configure Backend Services and Routes

Define upstream services and create routes to expose APIs.

**For Kong (using decK for declarative config):**
```bash
# Install decK CLI
curl -sL https://github.com/Kong/deck/releases/download/v1.28.0/deck_1.28.0_linux_amd64.tar.gz | tar -xz
sudo mv deck /usr/local/bin/

# Create kong.yaml with services, routes, upstreams
# (see EXAMPLES.md for complete configuration)
deck sync --kong-addr http://localhost:8001 -s kong.yaml
curl -i http://localhost:8001/routes  # Verify routes
```

**For Traefik (using IngressRoute CRD):**
```yaml
# traefik-routes.yaml (excerpt)
apiVersion: traefik.io/v1alpha1
kind: IngressRoute
metadata:
  name: user-api-route
spec:
  entryPoints: [websecure]
  routes:
  - match: Host(`api.example.com`) && PathPrefix(`/api/users`)
    # ... (see EXAMPLES.md for full configuration)
```

Apply routes:
```bash
kubectl apply -f traefik-routes.yaml
curl -H "Host: api.example.com" https://GATEWAY_IP/api/users
```

See [EXAMPLES.md](references/EXAMPLES.md#step-2-configure-backend-services-and-routes) for complete routing configurations

**Expected:** Routes correctly proxy traffic to backend services. Weighted routing distributes traffic according to configuration. Health checks monitor backend service health.

**On failure:**
- Verify backend services running: `kubectl get svc -n default`
- Check DNS resolution: `kubectl run test --rm -it --image=busybox -- nslookup user-service.default.svc.cluster.local`
- Review gateway logs: `kubectl logs -n kong -l app=kong --tail=50`
- Validate configuration: `deck validate -s kong.yaml`

### Step 3: Implement Authentication and Authorization

Configure authentication plugins/middleware for API security.

**For Kong (API Key and JWT authentication):**
```yaml
# kong-auth-config.yaml (excerpt)
consumers:
- username: mobile-app
  custom_id: app-001

keyauth_credentials:
- consumer: mobile-app
  key: mobile-secret-key-123

plugins:
- name: key-auth
  service: user-api
  # ... (see EXAMPLES.md for full configuration)
```

```bash
deck sync --kong-addr http://localhost:8001 -s kong-auth-config.yaml
curl -i -H "apikey: mobile-secret-key-123" http://GATEWAY_IP/api/users
```

**For Traefik (BasicAuth and ForwardAuth middleware):**
```yaml
# traefik-auth-middleware.yaml (excerpt)
apiVersion: traefik.io/v1alpha1
kind: Middleware
metadata:
  name: basic-auth-middleware
spec:
  basicAuth:
    secret: basic-auth
    removeHeader: true
# ... (see EXAMPLES.md for OAuth2, rate limiting)
```

```bash
kubectl apply -f traefik-auth-middleware.yaml
curl -u user1:password https://GATEWAY_IP/api/protected
```

See [EXAMPLES.md](references/EXAMPLES.md#step-3-implement-authentication-and-authorization) for complete authentication configurations

**Expected:** Unauthenticated requests return 401. Valid credentials allow access. Rate limiting returns 429 after threshold. JWT tokens validate correctly. ACL enforces group permissions.

**On failure:**
- Verify consumer creation: `curl http://localhost:8001/consumers`
- Check plugin enabled: `curl http://localhost:8001/plugins | jq .`
- Test with verbose: `curl -v` to see response headers
- Validate JWT: use jwt.io to decode token

### Step 4: Configure Request/Response Transformation

Add middleware to transform requests and responses.

**For Kong:**
```yaml
# kong-transformations.yaml (excerpt)
plugins:
- name: request-transformer
  service: user-api
  config:
    add:
      headers: [X-Gateway-Version:1.0, X-Request-ID:$(uuid)]
    remove:
      headers: [X-Internal-Token]
- name: correlation-id
  # ... (see EXAMPLES.md for full configuration)
```

```bash
deck sync --kong-addr http://localhost:8001 -s kong-transformations.yaml
```

**For Traefik:**
```yaml
# traefik-transformations.yaml (excerpt)
apiVersion: traefik.io/v1alpha1
kind: Middleware
metadata:
  name: add-headers
spec:
  headers:
    customRequestHeaders:
      X-Gateway-Version: "1.0"
    # ... (see EXAMPLES.md for circuit breaker, retry, chain)
```

```bash
kubectl apply -f traefik-transformations.yaml
curl -v https://GATEWAY_IP/api/users | grep X-Gateway
```

See [EXAMPLES.md](references/EXAMPLES.md#step-4-configure-requestresponse-transformation) for complete transformation configurations

**Expected:** Request headers added/removed as configured. Response headers include gateway metadata. Large requests rejected with 413. Circuit breaker trips on repeated failures. Retries occur for transient errors.

**On failure:**
- Verify middleware order in chain
- Check for header conflicts with backend services
- Test transformations individually before chaining
- Review logs for transformation errors

### Step 5: Enable Monitoring and Analytics

Configure metrics, logging, and dashboards for API visibility.

**Kong monitoring setup:**
```yaml
# kong-monitoring.yaml (excerpt)
plugins:
- name: prometheus
  config:
    per_consumer: true
- name: http-log
  service: user-api
  # ... (see EXAMPLES.md for Datadog, file-log configuration)
```

```bash
deck sync --kong-addr http://localhost:8001 -s kong-monitoring.yaml

# Deploy ServiceMonitor (see EXAMPLES.md)
kubectl apply -f kong-servicemonitor.yaml
curl http://localhost:8100/metrics
```

**Traefik monitoring (built-in):**
```yaml
# ServiceMonitor (excerpt - see EXAMPLES.md for Grafana dashboard)
apiVersion: monitoring.coreos.com/v1
kind: ServiceMonitor
metadata:
  name: traefik-metrics
spec:
  endpoints:
  - port: metrics
    path: /metrics
    interval: 30s
```

```bash
kubectl port-forward -n traefik svc/traefik-dashboard 8080:8080
# Open http://localhost:8080/dashboard/
```

See [EXAMPLES.md](references/EXAMPLES.md#step-5-enable-monitoring-and-analytics) for complete monitoring configurations

**Expected:** Prometheus scraping gateway metrics successfully. Dashboards show request rates, latency percentiles, error rates. Logs forwarding to aggregation system. Metrics segmented by service, route, and consumer.

**On failure:**
- Verify ServiceMonitor: `kubectl get servicemonitor -A`
- Check Prometheus targets in UI
- Ensure metrics port accessible: `kubectl port-forward -n kong svc/kong-metrics 8100:8100`
- Validate log endpoint reachability

### Step 6: Implement API Versioning and Deprecation

Configure version management and graceful API deprecation.

**Kong versioning strategy:**
```yaml
# kong-versioning.yaml (excerpt)
services:
- name: user-api-v1
  url: http://user-service-v1.default.svc.cluster.local:8080
  routes:
  - name: user-v1-route
    paths: [/api/v1/users]
  plugins:
  - name: response-transformer
    config:
      add:
        headers:
        - X-Deprecation-Notice:"API v1 deprecated on 2024-12-31"
        - Sunset:"Wed, 31 Dec 2024 23:59:59 GMT"
# ... (see EXAMPLES.md for v2, default routing, rate limits)
```

**Traefik versioning:**
```yaml
# traefik-versioning.yaml (excerpt)
apiVersion: traefik.io/v1alpha1
kind: Middleware
metadata:
  name: v1-deprecation-headers
spec:
  headers:
    customResponseHeaders:
      X-Deprecation-Notice: "API v1 deprecated on 2024-12-31"
# ... (see EXAMPLES.md for complete IngressRoutes)
```

Test versioning:
```bash
curl -i https://api.example.com/api/v1/users  # Deprecated
curl -i https://api.example.com/api/v2/users  # Current
curl -i https://api.example.com/api/users     # Routes to v2
```

See [EXAMPLES.md](references/EXAMPLES.md#step-6-implement-api-versioning-and-deprecation) for complete versioning configurations

**Expected:** Different versions route to appropriate backend services. Deprecation headers present on v1 responses. Rate limits stricter for deprecated versions. Default path routes to latest version. Metrics segmented by API version.

**On failure:**
- Verify path precedence/priority configuration (higher priority = evaluated first; more specific paths need higher priority)
- Check for overlapping path patterns (overlaps do not error — they silently cause unpredictable routing; verify the actual route hit with `curl -v`)
- Test each version route independently
- Review routing logs for path matching
- Ensure backend services for each version are running

## Validation

- [ ] API gateway pods running with multiple replicas for HA
- [ ] Load balancer service has external IP assigned
- [ ] Routes correctly proxy traffic to backend services
- [ ] Authentication/authorization enforcing access control (401/403 responses)
- [ ] Rate limiting returns 429 after exceeding quotas
- [ ] Request/response transformation adding/removing headers correctly
- [ ] Circuit breaker trips on repeated backend failures
- [ ] Metrics exposed and scraped by Prometheus
- [ ] Dashboards showing request rates, latency, errors
- [ ] API versioning routing requests to correct backend versions
- [ ] Deprecation headers present on older API versions
- [ ] Health checks monitoring backend service availability

## Common Pitfalls

- **Database Dependency (Kong)**: Kong with database requires PostgreSQL/Cassandra. DB-less mode available but limits some features (runtime config changes). Use DB mode for production with multiple gateway instances.

- **Authentication Bypass**: Ensure authentication plugins applied to all routes. Easy to add route without auth. Use default plugins at service level, then override per-route as needed.

- **Rate Limit Scope**: Rate limiting `policy: local` counts per gateway pod. For consistent limits across replicas, use centralized policy (Redis) or sticky sessions.

- **CORS Configuration**: API gateway should handle CORS, not individual services. Add CORS plugin/middleware early to avoid browser preflight failures.

- **Upstream Health Checks**: Configure active health checks to detect backend failures quickly. Passive checks rely on real traffic and may be slower to detect issues.

- **Plugin/Middleware Execution Order**: Order matters. Authentication before rate limiting (avoid wasted rate limit slots for invalid requests). Transformation before logging (log transformed values).

## Related Skills

- `configure-ingress-networking` - Ingress controller setup complements API gateway
- `setup-service-mesh` - Service mesh provides complementary east-west traffic management
- `manage-kubernetes-secrets` - Certificate and credential management for gateway
- `setup-prometheus-monitoring` - Monitoring integration for gateway metrics
- `enforce-policy-as-code` - Policy enforcement that complements gateway authorization