Architecture

This sections gives an overview of a Kuma service mesh. It also covers how to start integrating your services into your mesh.

A Kuma mesh consists of two main components:

• The data plane consists of the proxies that run alongside your services. All of your mesh traffic flows through these proxies on its way to its destination. Kuma’s uses Envoy for its data plane proxy.
• The control plane configures the data plane proxies for handling mesh traffic. However, the control plane runs independently of the data plane and does not interact with mesh traffic directly. Kuma users create policies that the Kuma control plane processes to generate configuration for the data plane proxies.

This is a high level visualization of a Kuma service mesh:

Communication happens between the control and data plane as well as between the services and their data plane proxies:

Components

A minimal Kuma deployment involves one or more instances of the control plane executable, kuma-cp. For each service in your mesh, you’ll have one or more instances of the data plane proxy executable, kuma-dp.

Users interact with the control plane via the command-line tool kumactl.

There are two modes that the Kuma control plane can run in:

• kubernetes: users configure Kuma via Kubernetes resources and Kuma uses the Kubernetes API server as the data store.
• universal: users configure Kuma via the Kuma API server and Kuma resources. PostgreSQL serves as the data store. This mode works for any infrastructure other than Kubernetes, though you can run a universal control plane on top of a Kubernetes cluster.

Kubernetes mode

When running in Kubernetes mode, Kuma stores all of its state and configuration on the underlying Kubernetes API Server.

The only step necessary to join your Kubernetes services to the mesh is enabling sidecar injection. For any Pods configured with sidecar injection, Kuma adds the kuma-dp sidecar container. The following label on any Namespace or Pod controls this injection:

kuma.io/sidecar-injection: enabled

Services and Pods

Pods with a Service

For all Pods associated with a Kubernetes Service resource, Kuma control plane automatically generates an annotation kuma.io/service: <name>_<namespace>_svc_<port> where <name>, <namespace> and <port> come from the Service. For example, the following resources generates kuma.io/service: echo-server_kuma-test_svc_80:

apiVersion: v1
kind: Service
metadata:
  name: echo-server
  namespace: kuma-test
  annotations:
    80.service.kuma.io/protocol: http
spec:
  ports:
    - port: 80
      name: http
  selector:
    app: echo-server
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: echo-server
  namespace: kuma-test
  labels:
    app: echo-server
spec:
  strategy:
    rollingUpdate:
      maxSurge: 1
      maxUnavailable: 0
  selector:
    matchLabels:
      app: echo-server
  template:
    metadata:
      labels:
        app: echo-server
    spec:
      containers:
        - name: echo-server
          image: nginx
          ports:
            - containerPort: 80

Pods without a Service

In some cases Pods don’t belong to a corresponding Service. This is typically because they don’t expose any consumable services. Kubernetes Jobs are a good example of this.

In this case, the Kuma control plane generates a kuma.io/service tag with the format <name>_<namespace>_svc, where <name> and<namespace> come from the Pod resource itself.

The Pods created by the following example Deployment have the tag kuma.io/service: echo-client_default_svc:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: echo-client
  labels:
    app: echo-client
spec:
  selector:
    matchLabels:
      app: echo-client
  template:
    metadata:
      labels:
        app: echo-client
    spec:
      containers:
        - name: alpine
          image: "alpine"
          imagePullPolicy: IfNotPresent
          command: ["sh", "-c", "tail -f /dev/null"]

Universal mode

When running in Universal mode, Kuma requires a PostgreSQL database to store its state. This replaces the Kubernetes API. With Universal, you use kumactl to interact directly with the Kuma API server to manage policies.

Read the docs about the PostgreSQL backend for more details.