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Establish cluster peering connections on Kubernetes

This page details the process for establishing a cluster peering connection between services in a Consul on Kubernetes deployment.

The overall process for establishing a cluster peering connection consists of the following steps:

  1. Create a peering token in one cluster.
  2. Use the peering token to establish peering with a second cluster.
  3. Export services between clusters.
  4. Create intentions to authorize services for peers.

Cluster peering between services cannot be established until all four steps are complete.

Cluster peering between services cannot be established until all four steps are complete. If you want to establish cluster peering connections and create sameness groups at the same time, refer to the guidance in create sameness groups.

For general guidance for establishing cluster peering connections, refer to Establish cluster peering connections.

Prerequisites

You must meet the following requirements to use Consul's cluster peering features with Kubernetes:

  • Consul v1.14.1 or higher
  • Consul on Kubernetes v1.0.0 or higher
  • At least two Kubernetes clusters

In Consul on Kubernetes, peers identify each other using the metadata.name values you establish when creating the PeeringAcceptor and PeeringDialer CRDs. For additional information about requirements for cluster peering on Kubernetes deployments, refer to Cluster peering on Kubernetes technical specifications.

Assign cluster IDs to environmental variables

After you provision a Kubernetes cluster and set up your kubeconfig file to manage access to multiple Kubernetes clusters, you can assign your clusters to environmental variables for future use.

  1. Get the context names for your Kubernetes clusters using one of these methods:

    • Run the kubectl config current-context command to get the context for the cluster you are currently in.
    • Run the kubectl config get-contexts command to get all configured contexts in your kubeconfig file.

  2. Use the kubectl command to export the Kubernetes context names and then set them to variables. For more information on how to use kubeconfig and contexts, refer to the Kubernetes docs on configuring access to multiple clusters.

    $ export CLUSTER1_CONTEXT=<CONTEXT for first Kubernetes cluster>
$ export CLUSTER2_CONTEXT=<CONTEXT for second Kubernetes cluster>

Install Consul using Helm and configure peering over mesh gateways

To use cluster peering with Consul on Kubernetes deployments, update the Helm chart with the required values. After updating the Helm chart, you can use the consul-k8s CLI to apply values.yaml to each cluster.

  1. In cluster-01, run the following commands:

    $ export HELM_RELEASE_NAME1=cluster-01

    $ helm install ${HELM_RELEASE_NAME1} hashicorp/consul --create-namespace --namespace consul --version "1.2.0" --values values.yaml --set global.datacenter=dc1 --kube-context $CLUSTER1_CONTEXT

  2. In cluster-02, run the following commands:

    $ export HELM_RELEASE_NAME2=cluster-02

    $ helm install ${HELM_RELEASE_NAME2} hashicorp/consul --create-namespace --namespace consul --version "1.2.0" --values values.yaml --set global.datacenter=dc2 --kube-context $CLUSTER2_CONTEXT

  3. For both clusters apply the Mesh configuration entry values provided in Mesh Gateway Specifications to allow establishing peering connections over mesh gateways.

Configure the mesh gateway mode for traffic between services

In Kubernetes deployments, you can configure mesh gateways to use local mode so that a service dialing a service in a remote peer dials the local mesh gateway instead of the remote mesh gateway. To configure the mesh gateway mode so that this traffic always leaves through the local mesh gateway, you can use the ProxyDefaults CRD.

  1. In cluster-01 apply the following ProxyDefaults CRD to configure the mesh gateway mode.

    proxy-defaults.yaml
    apiVersion: consul.hashicorp.com/v1alpha1
kind: ProxyDefaults
metadata:
  name: global
spec:
  meshGateway:
    mode: local

    $ kubectl --context $CLUSTER1_CONTEXT apply -f proxy-defaults.yaml

  2. In cluster-02 apply the following ProxyDefaults CRD to configure the mesh gateway mode.

    proxy-defaults.yaml
    apiVersion: consul.hashicorp.com/v1alpha1
kind: ProxyDefaults
metadata:
  name: global
spec:
  meshGateway:
    mode: local

    $ kubectl --context $CLUSTER2_CONTEXT apply -f proxy-defaults.yaml

Create a peering token

To begin the cluster peering process, generate a peering token in one of your clusters. The other cluster uses this token to establish the peering connection.

Every time you generate a peering token, a single-use secret for establishing the secret is embedded in the token. Because regenerating a peering token invalidates the previously generated secret, you must use the most recently created token to establish peering connections.

  1. In cluster-01, create the PeeringAcceptor custom resource. To ensure cluster peering connections are secure, the metadata.name field cannot be duplicated. Refer to the peer by a specific name.

    acceptor.yaml
    apiVersion: consul.hashicorp.com/v1alpha1
kind: PeeringAcceptor
metadata:
  name: cluster-02 ## The name of the peer you want to connect to
spec:
  peer:
    secret:
      name: "peering-token"
      key: "data"
      backend: "kubernetes"

  2. Apply the PeeringAcceptor resource to the first cluster.

    $ kubectl --context $CLUSTER1_CONTEXT apply --filename acceptor.yaml

  3. Save your peering token so that you can export it to the other cluster.

    $ kubectl --context $CLUSTER1_CONTEXT get secret peering-token --output yaml > peering-token.yaml

Establish a connection between clusters

Next, use the peering token to establish a secure connection between the clusters.

  1. Apply the peering token to the second cluster.

    $ kubectl --context $CLUSTER2_CONTEXT apply --filename peering-token.yaml

  2. In cluster-02, create the PeeringDialer custom resource. To ensure cluster peering connections are secure, the metadata.name field cannot be duplicated. Refer to the peer by a specific name.

    dialer.yaml
    apiVersion: consul.hashicorp.com/v1alpha1
kind: PeeringDialer
metadata:
  name: cluster-01 ## The name of the peer you want to connect to
spec:
  peer:
    secret:
      name: "peering-token"
      key: "data"
      backend: "kubernetes"

  3. Apply the PeeringDialer resource to the second cluster.

    $ kubectl --context $CLUSTER2_CONTEXT apply --filename dialer.yaml

Export services between clusters

After you establish a connection between the clusters, you need to create an exported-services CRD that defines the services that are available to another admin partition.

While the CRD can target admin partitions either locally or remotely, clusters peering always exports services to remote admin partitions. Refer to exported service consumers for more information.

  1. For the service in cluster-02 that you want to export, add the "consul.hashicorp.com/connect-inject": "true" annotation to your service's pods prior to deploying. The annotation allows the workload to join the mesh. It is highlighted in the following example:

    backend.yaml
    # Service to expose backend
apiVersion: v1
kind: Service
metadata:
  name: backend
spec:
  selector:
    app: backend
  ports:
  - name: http
    protocol: TCP
    port: 80
    targetPort: 9090
---
apiVersion: v1
kind: ServiceAccount
metadata:
  name: backend
---
# Deployment for backend
apiVersion: apps/v1
kind: Deployment
metadata:
  name: backend
  labels:
    app: backend
spec:
  replicas: 1
  selector:
    matchLabels:
      app: backend
  template:
    metadata:
      labels:
        app: backend
      annotations:
        "consul.hashicorp.com/connect-inject": "true"
    spec:
      serviceAccountName: backend
      containers:
      - name: backend
        image: nicholasjackson/fake-service:v0.22.4
        ports:
        - containerPort: 9090
        env:
        - name: "LISTEN_ADDR"
          value: "0.0.0.0:9090"
        - name: "NAME"
          value: "backend"
        - name: "MESSAGE"
          value: "Response from backend"

  2. Deploy the backend service to the second cluster.

    $ kubectl --context $CLUSTER2_CONTEXT apply --filename backend.yaml

  3. In cluster-02, create an ExportedServices custom resource. The name of the peer that consumes the service should be identical to the name set in the PeeringDialer CRD.

    exported-service.yaml
    apiVersion: consul.hashicorp.com/v1alpha1
kind: ExportedServices
metadata:
  name: default ## The name of the partition containing the service
spec:
  services:
    - name: backend ## The name of the service you want to export
      consumers:
      - peer: cluster-01 ## The name of the peer that receives the service

  4. Apply the ExportedServices resource to the second cluster.

    $ kubectl --context $CLUSTER2_CONTEXT apply --filename exported-service.yaml

Authorize services for peers

Before you can call services from peered clusters, you must set service intentions that authorize those clusters to use specific services. Consul prevents services from being exported to unauthorized clusters.

  1. Create service intentions for the second cluster. The name of the peer should match the name set in the PeeringDialer CRD.

    intention.yaml
    apiVersion: consul.hashicorp.com/v1alpha1
kind: ServiceIntentions
metadata:
  name: backend-deny
spec:
  destination:
    name: backend
  sources:
   - name: "*"
     action: deny
   - name: frontend
     action: allow
     peer: cluster-01 ## The peer of the source service

  2. Apply the intentions to the second cluster.

    $ kubectl --context $CLUSTER2_CONTEXT apply --filename intention.yaml

  3. Add the "consul.hashicorp.com/connect-inject": "true" annotation to your service's pods before deploying the workload so that the services in cluster-01 can dial backend in cluster-02. To dial the upstream service from an application, configure the application so that that requests are sent to the correct DNS name as specified in Service Virtual IP Lookups. In the following example, the annotation that allows the workload to join the mesh and the configuration provided to the workload that enables the workload to dial the upstream service using the correct DNS name is highlighted. Service Virtual IP Lookups for Consul Enterprise details how you would similarly format a DNS name including partitions and namespaces.

    frontend.yaml
    # Service to expose frontend
apiVersion: v1
kind: Service
metadata:
  name: frontend
spec:
  selector:
    app: frontend
  ports:
  - name: http
    protocol: TCP
    port: 9090
    targetPort: 9090
---
apiVersion: v1
kind: ServiceAccount
metadata:
  name: frontend
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: frontend
  labels:
    app: frontend
spec:
  replicas: 1
  selector:
    matchLabels:
      app: frontend
  template:
    metadata:
      labels:
        app: frontend
      annotations:
        "consul.hashicorp.com/connect-inject": "true"
    spec:
      serviceAccountName: frontend
      containers:
      - name: frontend
        image: nicholasjackson/fake-service:v0.22.4
        securityContext:
          capabilities:
            add: ["NET_ADMIN"]
        ports:
        - containerPort: 9090
        env:
        - name: "LISTEN_ADDR"
          value: "0.0.0.0:9090"
        - name: "UPSTREAM_URIS"
          value: "http://backend.virtual.cluster-02.consul"
        - name: "NAME"
          value: "frontend"
        - name: "MESSAGE"
          value: "Hello World"
        - name: "HTTP_CLIENT_KEEP_ALIVES"
          value: "false"

  4. Apply the service file to the first cluster.

    $ kubectl --context $CLUSTER1_CONTEXT apply --filename frontend.yaml

  5. Run the following command in frontend and then check the output to confirm that you peered your clusters successfully.

    $ kubectl --context $CLUSTER1_CONTEXT exec -it $(kubectl --context $CLUSTER1_CONTEXT get pod -l app=frontend -o name) -- curl localhost:9090

    {
  "name": "frontend",
  "uri": "/",
  "type": "HTTP",
  "ip_addresses": [
    "10.16.2.11"
  ],
  "start_time": "2022-08-26T23:40:01.167199",
  "end_time": "2022-08-26T23:40:01.226951",
  "duration": "59.752279ms",
  "body": "Hello World",
  "upstream_calls": {
    "http://backend.virtual.cluster-02.consul": {
      "name": "backend",
      "uri": "http://backend.virtual.cluster-02.consul",
      "type": "HTTP",
      "ip_addresses": [
        "10.32.2.10"
      ],
      "start_time": "2022-08-26T23:40:01.223503",
      "end_time": "2022-08-26T23:40:01.224653",
      "duration": "1.149666ms",
      "headers": {
        "Content-Length": "266",
        "Content-Type": "text/plain; charset=utf-8",
        "Date": "Fri, 26 Aug 2022 23:40:01 GMT"
      },
      "body": "Response from backend",
      "code": 200
    }
  },
  "code": 200
}
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