pjt222/agent-almanac/configure-api-gateway

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 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:

# 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:

# 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 for the complete deployment manifests

Deploy:

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):

# 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):

# 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:

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

See EXAMPLES.md 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):

# 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)

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):

# 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)

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

See EXAMPLES.md 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:

# 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)

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

For Traefik:

# 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)

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

See EXAMPLES.md 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:

# 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)

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):

# 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

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

See EXAMPLES.md 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:

# 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:

# 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:

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 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