Sidecar Patterns — Deep Dive

graph TD
    subgraph Pod
        App[Main Application]
        SC[Sidecar Container]
    end
    App <--> SC
    SC --> Ext[External Systems]

apiVersion: v1
kind: Pod
metadata:
  name: order-service
spec:
  containers:
    # Main application
    - name: order-app
      image: order-service:1.0
      ports:
        - containerPort: 8080
      volumeMounts:
        - name: logs
          mountPath: /var/log/app

    # Sidecar: Log forwarder
    - name: log-forwarder
      image: fluent/fluent-bit:latest
      volumeMounts:
        - name: logs
          mountPath: /var/log/app
          readOnly: true

  volumes:
    - name: logs
      emptyDir: {}

graph LR
    subgraph Pod
        App[Application]
        Amb[Ambassador - Envoy]
    end
    App -->|localhost| Amb
    Amb -->|mTLS, retry| Ext[External Service]

graph LR
    subgraph Pod A
        AppA[App A]
        EnvoyA[Envoy Sidecar]
    end
    subgraph Pod B
        EnvoyB[Envoy Sidecar]
        AppB[App B]
    end
    AppA --> EnvoyA
    EnvoyA -->|mTLS| EnvoyB
    EnvoyB --> AppB

graph LR
    subgraph Pod
        App[Application]
        Adp[Adapter]
    end
    App -->|Custom format| Adp
    Adp -->|Standard format| Mon[Monitoring System]

apiVersion: v1
kind: Pod
spec:
  containers:
    - name: app
      image: my-app:1.0
      # App exposes metrics at /internal-metrics in custom format

    - name: prometheus-exporter
      image: custom-exporter:1.0
      ports:
        - containerPort: 9090
          name: metrics
      # Converts /internal-metrics to Prometheus format at :9090/metrics

sequenceDiagram
    participant K as Kubelet
    participant I as Init Container
    participant M as Main Container
    K->>I: Start init container
    I->>I: Run initialization
    I->>K: Exit 0 (success)
    K->>M: Start main container

apiVersion: v1
kind: Pod
spec:
  initContainers:
    - name: wait-for-db
      image: busybox:1.28
      command: ['sh', '-c', 
        'until nc -z postgres-service 5432; do echo waiting for db; sleep 2; done']

    - name: run-migrations
      image: my-app:1.0
      command: ['./migrate.sh']
      env:
        - name: DATABASE_URL
          valueFrom:
            secretKeyRef:
              name: db-secret
              key: url

  containers:
    - name: app
      image: my-app:1.0

graph TD
    subgraph Control Plane
        CP[Istiod]
    end
    subgraph Data Plane
        subgraph Pod 1
            A1[App]
            E1[Envoy]
        end
        subgraph Pod 2
            A2[App]
            E2[Envoy]
        end
        subgraph Pod 3
            A3[App]
            E3[Envoy]
        end
    end
    CP --> E1
    CP --> E2
    CP --> E3
    E1 <--> E2
    E2 <--> E3

spec:
  containers:
    - name: app
      resources:
        requests:
          memory: "256Mi"
          cpu: "500m"
        limits:
          memory: "512Mi"
          cpu: "1000m"

    - name: envoy
      resources:
        requests:
          memory: "64Mi"
          cpu: "100m"
        limits:
          memory: "128Mi"
          cpu: "200m"