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"@type": "BlogPosting",
"headline": "API Gateway Engineer Interview Guide",
"description": "Master API gateway engineering interviews \u2014 reverse proxy architecture, rate limiting algorithms, JWT validation, request routing, circuit breakers.",
"datePublished": "2026-03-19",
"author": {
"@type": "Organization",
"name": "CodeSwiftr Team"
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"url": "https://codeswiftr.com/blog/api-gateway-engineer-interview-guide"
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{
"@context": "https://schema.org",
"@type": "FAQPage",
"mainEntity": [
{
"@type": "Question",
"name": "What does an API gateway engineer do and what do their interviews cover?",
"acceptedAnswer": {
"@type": "Answer",
"text": "API gateway engineers build and maintain the reverse proxy infrastructure that sits between clients and backend services: request routing, authentication and authorization enforcement, rate limiting, request/response transformation, SSL termination, logging, and observability. Interviews cover reverse proxy architecture (Nginx, Envoy, Kong, AWS API Gateway), rate limiting algorithm implementation, JWT validation at the edge, circuit breaker patterns (preventing cascade failures when backend services fail), request routing strategies (path-based, header-based, canary routing), and observability (distributed tracing with OpenTelemetry, request logging, error rate monitoring). Expect both system design questions and coding exercises implementing specific gateway components."
}
},
{
"@type": "Question",
"name": "What is a circuit breaker pattern and how does it apply to API gateways?",
"acceptedAnswer": {
"@type": "Answer",
"text": "A circuit breaker prevents a failing downstream service from cascading failures to the entire system. It works like an electrical circuit breaker: when a threshold of failures is detected (e.g., 50% error rate over 30 seconds), the circuit 'opens' and subsequent requests fail immediately without hitting the backend, giving the backend time to recover. After a configurable timeout, the circuit transitions to 'half-open' and allows a small number of probe requests through. If those succeed, the circuit closes and normal traffic resumes; if they fail, the circuit opens again. At an API gateway, circuit breakers protect against: database timeouts, slow backend services causing client thread exhaustion, and downstream service restarts. Resilience4j and Hystrix are common implementations; Envoy has built-in circuit breaking."
}
},
{
"@type": "Question",
"name": "How does JWT validation work at the API gateway layer?",
"acceptedAnswer": {
"@type": "Answer",
"text": "JWT validation at the gateway offloads authentication from individual backend services. The gateway receives an Authorization: Bearer {token} header, base64-decodes the JWT, and verifies the signature using the public key from the identity provider (fetched from a JWKS endpoint and cached). It then validates the claims: expiration (exp), audience (aud should match the service), and issuer (iss should match the expected identity provider). Valid tokens have their claims forwarded to backend services as trusted headers (X-User-ID, X-User-Roles) so backends can authorize without re-validating the JWT. The gateway rejects expired tokens, invalid signatures, and tokens with wrong audience claims with a 401 response. JWKS key caching requires periodic refresh to handle key rotation by the identity provider."
}
},
{
"@type": "Question",
"name": "What popular API gateway technologies should I know for engineering interviews?",
"acceptedAnswer": {
"@type": "Answer",
"text": "Key API gateway technologies to know: Kong (Nginx-based, plugin architecture, widely used in Kubernetes), Envoy (high-performance, used by Istio service mesh, strong observability), AWS API Gateway (managed, tight AWS integration, good for Lambda-backed APIs), Nginx (battle-tested reverse proxy, sometimes used as a lightweight gateway), and Traefik (cloud-native, automatic service discovery, popular in Kubernetes). For managed cloud providers: AWS API Gateway vs. Application Load Balancer (ALB) as a gateway, Google Cloud API Gateway, and Azure API Management. Be able to compare these on: performance characteristics, plugin ecosystem, observability, Kubernetes integration, and cost. Knowing that Envoy is the data plane underlying most modern service meshes (Istio, Linkerd) is a strong signal of infrastructure depth."
}
}
]
}