Configure Terminating Gateways for Consul on Kubernetes

Adding a terminating gateway is a multi-step process:

• Update the Helm chart with terminating gateway config options
• Deploy the Helm chart
• Access the Consul agent
• Register external services with Consul

Update the helm chart with terminating gateway config options

Minimum required Helm options:

global:
  name: consul
connectInject:
  enabled: true
controller:
  enabled: true
terminatingGateways:
  enabled: true

Deploying the Helm chart

Ensure you have the latest consul-helm chart and install Consul via helm using the following guide while being sure to provide the yaml configuration as previously discussed.

Accessing the Consul agent

You can access the Consul server directly from your host via kubectl port-forward. This is helpful for interacting with your Consul UI locally as well as to validate connectivity of the application.

$ kubectl port-forward consul-server-0 8500 &

If TLS is enabled use port 8501:

$ kubectl port-forward consul-server-0 8501 &

$ export CONSUL_HTTP_ADDR=http://localhost:8500

If TLS is enabled set:

$ export CONSUL_HTTP_ADDR=https://localhost:8501
$ export CONSUL_HTTP_SSL_VERIFY=false

If ACLs are enabled also set:

$ export CONSUL_HTTP_TOKEN=$(kubectl get secret consul-bootstrap-acl-token --template='{{.data.token | base64decode }}')

Register external services with Consul

Registering the external services with Consul is a multi-step process:

• Register external services with Consul
• Update the terminating gateway ACL token if ACLs are enabled
• Create a TerminatingGateway resource to configure the terminating gateway
• Create a ServiceIntentions resource to allow access from services in the mesh to external service
• Define upstream annotations for any services that need to talk to the external services

Register external services with Consul

Create a sample external service and register it with Consul.

{
  "Node": "example_com",
  "Address": "example.com",
  "NodeMeta": {
    "external-node": "true",
    "external-probe": "true"
  },
  "Service": {
    "Address": "example.com",
    "ID": "example-https",
    "Service": "example-https",
    "Port": 443
  }
}

• "Node": "example_com" is our made up node name.
• "Address": "example.com" is the address of our node. Services registered to that node will use this address if their own address isn't specified. If you're registering multiple external services, ensure you use different node names with different addresses or set the Service.Address key.
• "Service": { "Address": "example.com" ... } is the address of our service. In this example this doesn't need to be set since the address of the node is the same, but if there were two services registered to that same node then this should be set.

Register the external service with Consul:

$ curl --request PUT --data @external.json --insecure $CONSUL_HTTP_ADDR/v1/catalog/register
true

If ACLs and TLS are enabled :

$ curl --request PUT --header "X-Consul-Token: $CONSUL_HTTP_TOKEN" --data @external.json --insecure $CONSUL_HTTP_ADDR/v1/catalog/register
true

Update terminating gateway ACL token if ACLs are enabled

If ACLs are enabled, update the terminating gateway acl token to have service: write permissions on all of the services being represented by the gateway:

• Create a new policy that includes these permissions
• Update the existing token to include the new policy

service "example-https" {
  policy = "write"
}

$ consul acl policy create -name "example-https-write-policy" -rules @write-policy.hcl
ID:           xxxxxxxxxxxxxxx
Name:         example-https-write-policy
Description:
Datacenters:
Rules:
service "example-https" {
  policy = "write"
}

Now fetch the ID of the terminating gateway token

consul acl token list | grep -B 6 -- "- terminating-gateway-terminating-gateway-token" | grep AccessorID

AccessorID:       <token id>

Update the terminating gateway acl token with the new policy

$ consul acl token update -id <token-id> -policy-name example-https-write-policy -merge-policies -merge-roles -merge-service-identities
AccessorID:       <token id>
SecretID:         <secret id>
Description:      terminating-gateway-terminating-gateway-token Token
Local:            true
Create Time:      2021-01-08 21:18:47.957450486 +0000 UTC
Policies:
   63bf1d9b-a87d-8672-ddcb-d25e2d88adb8 - terminating-gateway-terminating-gateway-token
   f63d1ae6-ffe7-44bd-bf7a-704a86939a63 - example-https-write-policy

Create the configuration entry for the terminating gateway

Once the tokens have been updated, create the TerminatingGateway resource to configure the terminating gateway:

apiVersion: consul.hashicorp.com/v1alpha1
kind: TerminatingGateway
metadata:
  name: terminating-gateway
spec:
  services:
    - name: example-https
      caFile: /etc/ssl/cert.pem

Apply the TerminatingGateway resource with kubectl apply:

$ kubectl apply --filename terminating-gateway.yaml

If using ACLs and TLS, create a ServiceIntentions resource to allow access from services in the mesh to the external service

apiVersion: consul.hashicorp.com/v1alpha1
kind: ServiceIntentions
metadata:
  name: example-https
spec:
  destination:
    name: example-https
  sources:
    - name: static-client
      action: allow

Apply the ServiceIntentions resource with kubectl apply:

$ kubectl apply --filename service-intentions.yaml

Define the external services as upstreams for services in the mesh

Finally define and deploy the external services as upstreams for the internal mesh services that wish to talk to them. An example deployment is provided which will serve as a static client for the terminating gateway service.

apiVersion: v1
kind: Service
metadata:
  name: static-client
spec:
  selector:
    app: static-client
  ports:
    - port: 80
---
apiVersion: v1
kind: ServiceAccount
metadata:
  name: static-client
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: static-client
spec:
  replicas: 1
  selector:
    matchLabels:
      app: static-client
  template:
    metadata:
      name: static-client
      labels:
        app: static-client
      annotations:
        'consul.hashicorp.com/connect-inject': 'true'
        'consul.hashicorp.com/connect-service-upstreams': 'example-https:1234'
    spec:
      containers:
        - name: static-client
          image: curlimages/curl:latest
          command: ['/bin/sh', '-c', '--']
          args: ['while true; do sleep 30; done;']
      serviceAccountName: static-client

Run the service via kubectl apply:

$ kubectl apply --filename static-client.yaml

Wait for the service to be ready:

$ kubectl rollout status deploy static-client --watch
deployment "static-client" successfully rolled out

You can verify connectivity of the static-client and terminating gateway via a curl command:

$ kubectl exec deploy/static-client -- curl -vvvs --header "Host: example-https.com" http://localhost:1234/