Traffic Routing to Specific Microservices in AWS Using App Mesh

AWS App Mesh supports advanced traffic routing across microservices, including header-based routing. This method allows developers to route requests based on HTTP headers such as Accept, Cookie, or custom keys like canary_fleet.

Why Use Header-Based Routing?

Header-based routing helps support several use cases:

• Session persistence (sticky sessions)
  
• A/B testing via custom headers
  
• Canary or blue/green deployments
  
• Device-specific experiences (e.g., using regex on headers)
  
• Browser-based routing (e.g., using User-Agent)
  
• Access control based on IP or CDN (X-Forwarded-For)
  

Example: Route Canary Traffic Based on Header Value

In this example, we configure AWS App Mesh to route traffic only to the crystal-sd-epoch service if the request includes the header canary_fleet: true.

Create Traffic Routes

Instead of splitting traffic randomly across virtual nodes, the route directs traffic to the canary service only if the specified header is present.

# Define variables #
SPEC=$(cat <<-EOF
  { 
    "httpRoute": {
      "action": { 
        "weightedTargets": [
          {
            "virtualNode": "crystal-sd-epoch",
            "weight": 1
          }
        ]
      },
      "match": {
        "prefix": "/",
        "headers": [
          {
            "name": "canary_fleet",
            "match": {
              "exact": "true"
            }
          }
        ]
      }
    },
    "priority": 1
  }
EOF
); \
# Create app mesh route #
aws appmesh create-route \
  --mesh-name appmesh-workshop \
  --virtual-router-name crystal-router \
  --route-name crystal-header-route \
  --spec "$SPEC"

Check Results

Use the following script to test if you’re consistently receiving responses from the canary service:

# Define variables #
URL=$(jq < cfn-output.json -r '.ExternalLoadBalancerDNS');
# Execute curl #
for ((i=1;i<=15;i++)); do
  curl --location --silent --header "canary_fleet: true" $URL/json | jq ' .';
  sleep 2s
done

Benefits and Challenges of Microservice Routing

As applications scale, managing service-to-service traffic manually becomes a bottleneck. With hundreds of microservices, developers struggle to locate errors, update traffic flows, and safely roll out changes.

A service mesh like AWS App Mesh simplifies this by handling:

• Service discovery
  
• Traffic routing
  
• Observability
  
• Security policies
  
• Deployment control
  

This reduces the need to hardcode logic into each service and enables a centralized control plane.

However, it introduces its own complexities—especially for operations. Monitoring, backups, API gateways, CI/CD pipelines, and security enforcement must all be well-configured to benefit fully from the mesh model.

Zero-trust networking is also a key practice. Just because two services can communicate doesn’t mean they should. Enforcing policies at the service level, backed by a centralized registry, is essential for maintaining security and order in a microservices architecture.