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

There are two ways to register an external service with Consul:

1. If TransparentProxy is enabled, the preferred method is to declare external endpoints in the destination field of ServiceDefaults.
2. You can add the service as a node in the Consul catalog.

Register an external service as a destination

The destination field of the ServiceDefaults Custom Resource Definition (CRD) allows clients to dial the external service directly. It is valid only in TransparentProxy) mode. The following table describes traffic behaviors when using destinations to route traffic through a terminating gateway:

You can provide a caFile to secure traffic between unencrypted clients that connect to external services through the terminating gateway. Refer to Create the configuration entry for the terminating gateway for details.

Also note that regardless of the protocol specified in the ServiceDefaults, L7 intentions are not currently supported with ServiceDefaults destinations.

Create a ServiceDefaults custom resource for the external service:

  apiVersion: consul.hashicorp.com/v1alpha1
  kind: ServiceDefaults
  metadata:
    name: example-https
  spec:
    protocol: tcp
    destination:
      addresses:
        - "example.com"
      port: 443

Apply the ServiceDefaults resource with kubectl apply:

$ kubectl apply --filename serviceDefaults.yaml

All other terminating gateway operations can use the name of the ServiceDefaults in place of a typical Consul service name.

Register an external service as a Catalog Node

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 role if ACLs are enabled

If ACLs are enabled, update the terminating gateway acl role 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 role 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 role list | grep -B 6 -- "- RELEASE_NAME-terminating-gateway-policy" | grep ID

ID:       <role id>

Update the terminating gateway acl token with the new policy

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

Create the configuration entry for the terminating gateway

Once the roles 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

If TLS is enabled for external services registered through the Consul catalog and you are not using transparent proxy destination, you must include the caFile parameter that points to the system trust store of the terminating gateway container. By default, the trust store is located in the /etc/ssl/certs/ca-certificates.crt directory. Configure the caFile parameter in the TerminatingGateway config entry to point to the /etc/ssl/cert.pem directory if TLS is enabled and you are using one of the following components:

• Consul Helm chart 0.43 or older
• An Envoy image with an alpine base image

For ServiceDefaults destinations, refer to Register an external service as a destination.

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/

$ kubectl exec deploy/static-client -- curl -vvvs https://example.com/