February 26, 2025 14 min to read

Service Mesh vs API Gateway - Understanding the Differences

Learn about Service Mesh and API Gateway, two essential components in Kubernetes architecture

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Introduction

In modern microservices architectures, particularly those running on Kubernetes, two critical components have emerged to manage different aspects of network communication: Service Mesh and API Gateway. Though they may appear similar at first glance, they serve distinct purposes and solve different challenges.

This guide explores the differences between Service Mesh and API Gateway, their key features, implementation patterns, and when to use each in your Kubernetes architecture.

Service Mesh Deep Dive

What is a Service Mesh?

A Service Mesh is a dedicated infrastructure layer that controls service-to-service communication over a network. It provides capabilities like traffic management, observability, and security features without requiring changes to application code.

Core Components of a Service Mesh

1. Data Plane: Consists of lightweight proxies (sidecars) deployed alongside service instances. These proxies:
   • Intercept all network traffic
   • Apply policies
   • Collect metrics
   • Handle retries, circuit breaking, and timeouts
2. Control Plane: Manages and configures the proxies to enforce policies:
   • Service discovery
   • Certificate management
   • Policy distribution
   • Metrics aggregation

Key Features of Service Mesh

Sidecar Pattern in Depth

The Sidecar Pattern is the foundational implementation pattern for service meshes in Kubernetes. In this pattern:

apiVersion: v1
kind: Pod
metadata:
  name: service-a
spec:
  containers:
  - name: service-a
    image: service-a:latest
    ports:
    - containerPort: 8080
  - name: sidecar-proxy
    image: envoy:latest
    ports:
    - containerPort: 15000  # Admin
    - containerPort: 15001  # Ingress
    - containerPort: 15006  # Egress

Popular Service Mesh Solutions

API Gateway Deep Dive

What is an API Gateway?

An API Gateway is a server that acts as an API front-end, receives API requests, enforces throttling and security policies, passes requests to backend services, and then passes responses back to requesters. It serves as a single entry point for all clients.

Core Components of an API Gateway

1. Gateway Router: Routes external requests to the appropriate internal services
2. Authentication & Authorization: Secures access to backend services
3. Rate Limiting & Throttling: Controls traffic to protect backend services
4. Transformation Layer: Transforms requests/responses between clients and services
5. Analytics & Monitoring: Tracks API usage and performance

Key Features of API Gateways

Ambassador Pattern in Depth

The Ambassador Pattern is a design pattern where a service instance is deployed alongside a proxy application (ambassador) that handles network-related concerns.

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: api-gateway-ingress
  annotations:
    kubernetes.io/ingress.class: "nginx"
    nginx.ingress.kubernetes.io/rewrite-target: /
spec:
  rules:
  - host: api.example.com
    http:
      paths:
      - path: /users
        pathType: Prefix
        backend:
          service:
            name: user-service
            port:
              number: 80
      - path: /products
        pathType: Prefix
        backend:
          service:
            name: product-service
            port:
              number: 80

Popular API Gateway Solutions for Kubernetes

In-Depth Comparison: Service Mesh vs API Gateway

While both technologies manage network communication, they serve fundamentally different purposes in a microservices architecture.

Key Differences - Extended

Feature Overlap

Some features appear in both Service Mesh and API Gateway solutions, but with different implementations and focuses:

Practical Implementation Guide

Implementing Both: A Layered Approach

In modern Kubernetes architectures, it’s common to use both API Gateway and Service Mesh in a layered approach:

Implementation Example: Istio Service Mesh with Kong API Gateway

1. Install Istio Service Mesh

# Download Istio
curl -L https://istio.io/downloadIstio | sh -

# Install Istio with demo profile
istioctl install --set profile=demo -y

# Enable automatic sidecar injection in the default namespace
kubectl label namespace default istio-injection=enabled

2. Install Kong API Gateway

# Add Kong Helm repository
helm repo add kong https://charts.konghq.com
helm repo update

# Install Kong
helm install kong kong/kong -n kong --create-namespace

3. Deploy a Sample Microservice Application

# service-a.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: service-a
spec:
  replicas: 2
  selector:
    matchLabels:
      app: service-a
  template:
    metadata:
      labels:
        app: service-a
    spec:
      containers:
      - name: service-a
        image: service-a:latest
        ports:
        - containerPort: 8080
---
apiVersion: v1
kind: Service
metadata:
  name: service-a
spec:
  selector:
    app: service-a
  ports:
  - port: 80
    targetPort: 8080

4. Configure Kong API Gateway Ingress

# kong-ingress.yaml
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: api-gateway
  annotations:
    konghq.com/strip-path: "true"
spec:
  ingressClassName: kong
  rules:
  - host: api.example.com
    http:
      paths:
      - path: /service-a
        pathType: Prefix
        backend:
          service:
            name: service-a
            port:
              number: 80

5. Configure Istio Service Mesh Policies

# istio-policies.yaml
apiVersion: security.istio.io/v1beta1
kind: PeerAuthentication
metadata:
  name: default-mtls
  namespace: default
spec:
  mtls:
    mode: STRICT
---
apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: service-routing
spec:
  hosts:
  - service-a
  http:
  - route:
    - destination:
        host: service-a
    retries:
      attempts: 3
      perTryTimeout: 2s

Making the Right Choice

Decision Framework

When deciding between Service Mesh, API Gateway, or both, consider:

1. Architecture Complexity:
   • Simple → API Gateway might be sufficient
   • Complex → Service Mesh benefits increase
2. Team Structure:
   • Single team → Start with API Gateway
   • Multiple teams → Service Mesh helps with standardization
3. Security Requirements:
   • Basic authentication → API Gateway
   • Zero-trust, service identity → Service Mesh
4. Observability Needs:
   • API metrics → API Gateway
   • Service interactions → Service Mesh

Summary

References

• Wallarm - API Gateway vs Service Mesh
• XenonStack - Service Mesh vs API Gateway
• Microsoft - Sidecar Pattern
• Microsoft - Ambassador Pattern
• Istio Documentation
• Kong API Gateway Documentation
• CNCF - Service Mesh Interface Specification
• Solo.io - API Gateway vs Service Mesh