candela-sidecar

The Candela Sidecar is a lightweight Go proxy (< 5MB) built for production container environments. It provides LLM request proxying, OpenTelemetry tracing, cost calculation, and budget enforcement with minimal overhead.

Key Features

• Zero-config GCP auth via Application Default Credentials (ADC)
• W3C Trace Context propagation — traceparent/tracestate headers
• Async span export via Google Cloud Pub/Sub or OTLP
• Cost calculation with the shared costcalc engine
• Budget enforcement via Firestore
• Single static binary — < 5MB, no runtime dependencies

Supported Providers

Route	Provider	Auth
/proxy/google/*	Google Gemini (native format)	ADC
/proxy/openai/*	OpenAI API	API key in config
/proxy/anthropic/*	Anthropic (via Vertex AI)	ADC

Configuration

Environment variables:

Variable	Required	Description
GCP_PROJECT	✅	GCP project for Vertex AI and Pub/Sub
GCP_REGION		Vertex AI region (default: us-central1)
PUBSUB_TOPIC		Pub/Sub topic for span export
OTLP_ENDPOINT		OTLP HTTP endpoint for span export
PORT		Listen port (default: 8080)
FIRESTORE_DB		Firestore database for budget enforcement

Deployment

Docker

docker run -p 8080:8080 \
  -e GCP_PROJECT=my-project \
  -e PUBSUB_TOPIC=candela-spans \
  ghcr.io/candelahq/candela-sidecar:latest

Kubernetes

apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-app
spec:
  template:
    spec:
      containers:
        - name: app
          image: my-app:latest
          env:
            - name: LLM_BASE_URL
              value: "http://localhost:8080/proxy/google"
        - name: candela-sidecar
          image: ghcr.io/candelahq/candela-sidecar:latest
          ports:
            - containerPort: 8080
          env:
            - name: GCP_PROJECT
              value: my-project
            - name: PUBSUB_TOPIC
              value: candela-spans
          resources:
            requests:
              memory: "32Mi"
              cpu: "50m"
            limits:
              memory: "64Mi"
              cpu: "100m"

Cloud Run (Multi-Container)

service.yaml

apiVersion: serving.knative.dev/v1
kind: Service
metadata:
  name: my-service
spec:
  template:
    spec:
      containers:
        - image: my-app:latest
          ports:
            - containerPort: 3000
        - image: ghcr.io/candelahq/candela-sidecar:latest
          env:
            - name: GCP_PROJECT
              value: my-project

Sidecar vs. Server

	candela-sidecar	candela-server
Best for	Containers, CI, production	Local dev with UI
Size	< 5MB binary	Full server
Storage	Pub/Sub + OTLP export	DuckDB, SQLite, BigQuery
Budget enforcement	Yes (via Firestore)	Yes (via local store)
UI	None	Dashboard at :3000
Default port	:8080	:8181

Health Check

curl http://localhost:8080/healthz

Related

• ADK Integration — Route ADK agents through the sidecar
• Architecture — Storage backend details