Single Consul Datacenter in Multiple Kubernetes Clusters

Requires consul-helm v0.32.1 or higher.

This page describes how to deploy a single Consul datacenter in multiple Kubernetes clusters, with both servers and clients running in one cluster, and only clients running in the rest of the clusters. In this example, we will use two Kubernetes clusters, but this approach could be extended to using more than two.

Note: This deployment topology requires that your Kubernetes clusters have a flat network for both pods and nodes, so that pods or nodes from one cluster can connect to pods or nodes in another. If a flat network is not available across all Kubernetes clusters, follow the instructions for using Admin Partitions, which is a Consul Enterprise feature.

Prepare Helm release name ahead of installs

The Helm release name must be unique for each Kubernetes cluster. The Helm chart uses the Helm release name as a prefix for the ACL resources that it creates, such as tokens and auth methods. If the names of the Helm releases are identical, subsequent Consul on Kubernetes clusters overwrite existing ACL resources and cause the clusters to fail.

Before you proceed with installation, prepare the Helm release names as environment variables for both the server and client installs to use.

  1.   $ export HELM_RELEASE_SERVER=server
  2.   $ export HELM_RELEASE_CLIENT=client
  3.   ...
  4.   $ export HELM_RELEASE_CLIENT2=client2
  1.   $ export HELM_RELEASE_SERVER=server
  2.   $ export HELM_RELEASE_CLIENT=client
  3.   ...
  4.   $ export HELM_RELEASE_CLIENT2=client2

Deploying Consul servers and clients in the first cluster

First, we will deploy the Consul servers with Consul clients in the first cluster. For that, we will use the following Helm configuration:

  1. global:
  2.   datacenter: dc1
  3.   tls:
  4.     enabled: true
  5.     enableAutoEncrypt: true
  6.   acls:
  7.     manageSystemACLs: true
  8.   gossipEncryption:
  9.     secretName: consul-gossip-encryption-key
  10.     secretKey: key
  11. connectInject:
  12.   enabled: true
  13. controller:
  14.   enabled: true
  15. ui:
  16.   service:
  17.     type: NodePort

Single Consul Datacenter in Multiple Kubernetes Clusters - 图1

cluster1-config.yaml

  1. global:
  2.   datacenter: dc1
  3.   tls:
  4.     enabled: true
  5.     enableAutoEncrypt: true
  6.   acls:
  7.     manageSystemACLs: true
  8.   gossipEncryption:
  9.     secretName: consul-gossip-encryption-key
  10.     secretKey: key
  11. connectInject:
  12.   enabled: true
  13. controller:
  14.   enabled: true
  15. ui:
  16.   service:
  17.     type: NodePort

Note that we are deploying in a secure configuration, with gossip encryption, TLS for all components, and ACLs. We are enabling the Consul Service Mesh and the controller for CRDs so that we can use them to later verify that our services can connect with each other across clusters.

We’re also setting UI’s service type to be NodePort. This is needed so that we can connect to servers from another cluster without using the pod IPs of the servers, which are likely going to change.

To deploy, first we need to generate the Gossip encryption key and save it as a Kubernetes secret.

  1. $ kubectl create secret generic consul-gossip-encryption-key --from-literal=key=$(consul keygen)
  1. $ kubectl create secret generic consul-gossip-encryption-key --from-literal=key=$(consul keygen)

Now we can install our Consul cluster with Helm:

  1. $ helm install ${HELM_RELEASE_SERVER} --values cluster1-config.yaml hashicorp/consul
  1. $ helm install ${HELM_RELEASE_SERVER} --values cluster1-config.yaml hashicorp/consul

Once the installation finishes and all components are running and ready, we need to extract the gossip encryption key we’ve created, the CA certificate and the ACL bootstrap token generated during installation, so that we can apply them to our second Kubernetes cluster.

  1. $ kubectl get secret consul-gossip-encryption-key ${HELM_RELEASE_SERVER}-consul-ca-cert ${HELM_RELEASE_SERVER}-consul-bootstrap-acl-token --output yaml > cluster1-credentials.yaml
  1. $ kubectl get secret consul-gossip-encryption-key ${HELM_RELEASE_SERVER}-consul-ca-cert ${HELM_RELEASE_SERVER}-consul-bootstrap-acl-token --output yaml > cluster1-credentials.yaml

Deploying Consul clients in the second cluster

Note: If multiple Kubernetes clusters will be joined to the Consul Datacenter, then the following instructions will need to be repeated for each additional Kubernetes cluster.

Now we can switch to the second Kubernetes cluster where we will deploy only the Consul clients that will join the first Consul cluster.

First, we need to apply credentials we’ve extracted from the first cluster to the second cluster:

  1. $ kubectl apply --filename cluster1-credentials.yaml
  1. $ kubectl apply --filename cluster1-credentials.yaml

To deploy in the second cluster, we will use the following Helm configuration:

  1. global:
  2.   enabled: false
  3.   datacenter: dc1
  4.   acls:
  5.     manageSystemACLs: true
  6.     bootstrapToken:
  7.       secretName: cluster1-consul-bootstrap-acl-token
  8.       secretKey: token
  9.   gossipEncryption:
  10.     secretName: consul-gossip-encryption-key
  11.     secretKey: key
  12.   tls:
  13.     enabled: true
  14.     enableAutoEncrypt: true
  15.     caCert:
  16.       secretName: cluster1-consul-ca-cert
  17.       secretKey: tls.crt
  18. externalServers:
  19.   enabled: true
  20.   # This should be any node IP of the first k8s cluster
  21.   hosts: ["10.0.0.4"]
  22.   # The node port of the UI's NodePort service
  23.   httpsPort: 31557
  24.   tlsServerName: server.dc1.consul
  25.   # The address of the kube API server of this Kubernetes cluster
  26.   k8sAuthMethodHost: https://kubernetes.example.com:443
  27. client:
  28.   enabled: true
  29.   join: ["provider=k8s kubeconfig=/consul/userconfig/cluster1-kubeconfig/kubeconfig label_selector=\"app=consul,component=server\""]
  30.   extraVolumes:
  31.     - type: secret
  32.       name: cluster1-kubeconfig
  33.       load: false
  34. connectInject:
  35.   enabled: true

Single Consul Datacenter in Multiple Kubernetes Clusters - 图2

cluster2-config.yaml

  1. global:
  2.   enabled: false
  3.   datacenter: dc1
  4.   acls:
  5.     manageSystemACLs: true
  6.     bootstrapToken:
  7.       secretName: cluster1-consul-bootstrap-acl-token
  8.       secretKey: token
  9.   gossipEncryption:
  10.     secretName: consul-gossip-encryption-key
  11.     secretKey: key
  12.   tls:
  13.     enabled: true
  14.     enableAutoEncrypt: true
  15.     caCert:
  16.       secretName: cluster1-consul-ca-cert
  17.       secretKey: tls.crt
  18. externalServers:
  19.   enabled: true
  20.   # This should be any node IP of the first k8s cluster
  21.   hosts: ["10.0.0.4"]
  22.   # The node port of the UI's NodePort service
  23.   httpsPort: 31557
  24.   tlsServerName: server.dc1.consul
  25.   # The address of the kube API server of this Kubernetes cluster
  26.   k8sAuthMethodHost: https://kubernetes.example.com:443
  27. client:
  28.   enabled: true
  29.   join: ["provider=k8s kubeconfig=/consul/userconfig/cluster1-kubeconfig/kubeconfig label_selector=\"app=consul,component=server\""]
  30.   extraVolumes:
  31.     - type: secret
  32.       name: cluster1-kubeconfig
  33.       load: false
  34. connectInject:
  35.   enabled: true

Note that we’re referencing secrets from the first cluster in ACL, gossip, and TLS configuration.

Next, we need to set up the externalServers configuration.

The externalServers.hosts and externalServers.httpsPort refer to the IP and port of the UI’s NodePort service deployed in the first cluster. Set the externalServers.hosts to any Node IP of the first cluster, which you can see by running kubectl get nodes --output wide. Set externalServers.httpsPort to the nodePort of the cluster1-consul-ui service. In our example, the port is 31557.

  1. $ kubectl get service cluster1-consul-ui --context cluster1
  2. NAME                 TYPE       CLUSTER-IP    EXTERNAL-IP   PORT(S)         AGE
  3. cluster1-consul-ui   NodePort   10.0.240.80   <none>        443:31557/TCP   40h
  1. $ kubectl get service cluster1-consul-ui --context cluster1
  2. NAME                 TYPE       CLUSTER-IP    EXTERNAL-IP   PORT(S)         AGE
  3. cluster1-consul-ui   NodePort   10.0.240.80   <none>        443:31557/TCP   40h

We set the externalServer.tlsServerName to server.dc1.consul. This the DNS SAN (Subject Alternative Name) that is present in the Consul server’s certificate. We need to set it because we’re connecting to the Consul servers over the node IP, but that IP isn’t present in the server’s certificate. To make sure that the hostname verification succeeds during the TLS handshake, we need to set the TLS server name to a DNS name that is present in the certificate.

Next, we need to set externalServers.k8sAuthMethodHost to the address of the second Kubernetes API server. This should be the address that is reachable from the first cluster, and so it cannot be the internal DNS available in each Kubernetes cluster. Consul needs it so that consul login with the Kubernetes auth method will work from the second cluster. More specifically, the Consul server will need to perform the verification of the Kubernetes service account whenever consul login is called, and to verify service accounts from the second cluster it needs to reach the Kubernetes API in that cluster. The easiest way to get it is to set it from your kubeconfig by running kubectl config view and grabbing the value of cluster.server for the second cluster.

Lastly, we need to set up the clients so that they can discover the servers in the first cluster. For this, we will use Consul’s cloud auto-join feature for the Kubernetes provider. To use it we need to provide a way for the Consul clients to reach the first Kubernetes cluster. To do that, we need to save the kubeconfig for the first cluster as a Kubernetes secret in the second cluster and reference it in the clients.join value. Note that we’re making that secret available to the client pods by setting it in client.extraVolumes.

Note: The kubeconfig you’re providing to the client should have minimal permissions. The cloud auto-join provider will only need permission to read pods. Please see Kubernetes Cloud auto-join for more details.

Now we’re ready to install!

  1. $ helm install ${HELM_RELEASE_CLIENT} --values cluster2-config.yaml hashicorp/consul
  1. $ helm install ${HELM_RELEASE_CLIENT} --values cluster2-config.yaml hashicorp/consul

Verifying the Consul Service Mesh works

When Transparent proxy is enabled, services in one Kubernetes cluster that need to communicate with a service in another Kubernetes cluster must have a explicit upstream configured through the “consul.hashicorp.com/connect-service-upstreams” annotation.

Now that we have our Consul cluster in multiple k8s clusters up and running, we will deploy two services and verify that they can connect to each other.

First, we’ll deploy static-server service in the first cluster:

  1. ---
  2. apiVersion: consul.hashicorp.com/v1alpha1
  3. kind: ServiceIntentions
  4. metadata:
  5.   name: static-server
  6. spec:
  7.   destination:
  8.     name: static-server
  9.   sources:
  10.     - name: static-client
  11.       action: allow
  12. ---
  13. apiVersion: v1
  14. kind: Service
  15. metadata:
  16.   name: static-server
  17. spec:
  18.   type: ClusterIP
  19.   selector:
  20.     app: static-server
  21.   ports:
  22.     - protocol: TCP
  23.       port: 80
  24.       targetPort: 8080
  25. ---
  26. apiVersion: v1
  27. kind: ServiceAccount
  28. metadata:
  29.   name: static-server
  30. ---
  31. apiVersion: apps/v1
  32. kind: Deployment
  33. metadata:
  34.   name: static-server
  35. spec:
  36.   replicas: 1
  37.   selector:
  38.     matchLabels:
  39.       app: static-server
  40.   template:
  41.     metadata:
  42.       name: static-server
  43.       labels:
  44.         app: static-server
  45.       annotations:
  46.         "consul.hashicorp.com/connect-inject": "true"
  47.     spec:
  48.       containers:
  49.         - name: static-server
  50.           image: hashicorp/http-echo:latest
  51.           args:
  52.             - -text="hello world"
  53.             - -listen=:8080
  54.           ports:
  55.             - containerPort: 8080
  56.               name: http
  57.       serviceAccountName: static-server

Single Consul Datacenter in Multiple Kubernetes Clusters - 图3

static-server.yaml

  1. ---
  2. apiVersion: consul.hashicorp.com/v1alpha1
  3. kind: ServiceIntentions
  4. metadata:
  5.   name: static-server
  6. spec:
  7.   destination:
  8.     name: static-server
  9.   sources:
  10.     - name: static-client
  11.       action: allow
  12. ---
  13. apiVersion: v1
  14. kind: Service
  15. metadata:
  16.   name: static-server
  17. spec:
  18.   type: ClusterIP
  19.   selector:
  20.     app: static-server
  21.   ports:
  22.     - protocol: TCP
  23.       port: 80
  24.       targetPort: 8080
  25. ---
  26. apiVersion: v1
  27. kind: ServiceAccount
  28. metadata:
  29.   name: static-server
  30. ---
  31. apiVersion: apps/v1
  32. kind: Deployment
  33. metadata:
  34.   name: static-server
  35. spec:
  36.   replicas: 1
  37.   selector:
  38.     matchLabels:
  39.       app: static-server
  40.   template:
  41.     metadata:
  42.       name: static-server
  43.       labels:
  44.         app: static-server
  45.       annotations:
  46.         "consul.hashicorp.com/connect-inject": "true"
  47.     spec:
  48.       containers:
  49.         - name: static-server
  50.           image: hashicorp/http-echo:latest
  51.           args:
  52.             - -text="hello world"
  53.             - -listen=:8080
  54.           ports:
  55.             - containerPort: 8080
  56.               name: http
  57.       serviceAccountName: static-server

Note that we’re defining a Service intention so that our services are allowed to talk to each other.

Then we’ll deploy static-client in the second cluster with the following configuration:

  1. apiVersion: v1
  2. kind: Service
  3. metadata:
  4.   name: static-client
  5. spec:
  6.   selector:
  7.     app: static-client
  8.   ports:
  9.     - port: 80
  10. ---
  11. apiVersion: v1
  12. kind: ServiceAccount
  13. metadata:
  14.   name: static-client
  15. ---
  16. apiVersion: apps/v1
  17. kind: Deployment
  18. metadata:
  19.   name: static-client
  20. spec:
  21.   replicas: 1
  22.   selector:
  23.     matchLabels:
  24.       app: static-client
  25.   template:
  26.     metadata:
  27.       name: static-client
  28.       labels:
  29.         app: static-client
  30.       annotations:
  31.         "consul.hashicorp.com/connect-inject": "true"
  32.         "consul.hashicorp.com/connect-service-upstreams": "static-server:1234"
  33.     spec:
  34.       containers:
  35.         - name: static-client
  36.           image: curlimages/curl:latest
  37.           command: [ "/bin/sh", "-c", "--" ]
  38.           args: [ "while true; do sleep 30; done;" ]
  39.       serviceAccountName: static-client

Single Consul Datacenter in Multiple Kubernetes Clusters - 图4

static-client.yaml

  1. apiVersion: v1
  2. kind: Service
  3. metadata:
  4.   name: static-client
  5. spec:
  6.   selector:
  7.     app: static-client
  8.   ports:
  9.     - port: 80
  10. ---
  11. apiVersion: v1
  12. kind: ServiceAccount
  13. metadata:
  14.   name: static-client
  15. ---
  16. apiVersion: apps/v1
  17. kind: Deployment
  18. metadata:
  19.   name: static-client
  20. spec:
  21.   replicas: 1
  22.   selector:
  23.     matchLabels:
  24.       app: static-client
  25.   template:
  26.     metadata:
  27.       name: static-client
  28.       labels:
  29.         app: static-client
  30.       annotations:
  31.         "consul.hashicorp.com/connect-inject": "true"
  32.         "consul.hashicorp.com/connect-service-upstreams": "static-server:1234"
  33.     spec:
  34.       containers:
  35.         - name: static-client
  36.           image: curlimages/curl:latest
  37.           command: [ "/bin/sh", "-c", "--" ]
  38.           args: [ "while true; do sleep 30; done;" ]
  39.       serviceAccountName: static-client

Once both services are up and running, we can connect to the static-server from static-client:

  1. $ kubectl exec deploy/static-client -- curl --silent localhost:1234
  2. "hello world"
  1. $ kubectl exec deploy/static-client -- curl --silent localhost:1234
  2. "hello world"