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Consul Connect, the built-in service mesh of Consul, uses sidecar proxies to secure and manage traffic between services. By registering a sidecar proxy alongside your application, Consul can automatically route and secure calls through TLS-encrypted channels.
Registering a service proxy in Consul does not launch it. You still need to start the proxy process (either Consul’s built-in proxy or an external proxy such as Envoy).
Key tasks:
TaskDescription
1. Register the proxyAdd a connect.sidecar_service stanza in your service config
2. Start the proxyLaunch with consul connect proxy -sidecar-for <service>

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1. Registering via Configuration File

Instead of the HTTP API, declare your sidecar proxy in the same JSON or HCL file as your primary service. Include a connect block with an empty sidecar_service object: 
{
  "service": {
    "name": "front-end-ecommerce",
    "port": 8080,
    "connect": {
      "sidecar_service": {}
    }
  }
}
  • "name": Service identifier (e.g., front-end-ecommerce).
  • "port": Port your application listens on.
  • "connect.sidecar_service": {}: Signals Consul to register an integrated sidecar proxy.
Verify both the service and its proxy via the Consul UI or API.

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2. Adding Upstream Dependencies

Declare downstream services under proxy.upstreams within the sidecar_service block: 
{
  "service": {
    "id": "web-01",
    "name": "front-end-ecommerce",
    "tags": ["v7.05", "production"],
    "address": "",
    "port": 8080,
    "connect": {
      "sidecar_service": {
        "proxy": {
          "upstreams": [
            {
              "destination_name": "db01"
            }
          ]
        }
      }
    }
  }
}
  • "id": Unique instance identifier.
  • "tags": Metadata (version, environment).
  • "address": If empty, defaults to the local agent address.
  • "connect.sidecar_service.proxy.upstreams": List of target services.
    • "destination_name": Consul-registered name of the downstream service.
To add more dependencies, append additional objects to the upstreams list.
"upstreams": [
  { "destination_name": "db01" },
  { "destination_name": "api-service" }
]

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3. Deploying and Starting the Sidecar Proxy

  1. Place your JSON file in Consul’s configuration directory (e.g., /etc/consul.d/).
  2. Reload or restart the Consul agent:
    • consul reload
    • or systemctl restart consul
  3. Launch the proxy process:
    consul connect proxy -sidecar-for front-end-ecommerce
After these steps, both the application and its sidecar proxy are registered and active. Verify connectivity in the Consul UI, via the CLI, or using the API.

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References

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