Terminating Gateways on Kubernetes

1.8.0+: This feature is available in Consul versions 1.8.0 and higher

0.16.0+: This feature is available in consul-k8s versions 0.16.0 and higher

This topic requires familiarity with Terminating Gateways.

Terminating gateways are a new feature included in Consul 1.8. The correlating consul-k8s binary version is 0.16.0, and is required to enable terminating gateways. If you are using the latest official consul-helm chart, and have not customized the imageK8S configuration for any of your components, you should be running a compatible version by default.

Adding a terminating gateway is a multi-step process:

• Update the helm chart with terminating gateway config options
• Deploying the helm chart
• Accessing 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
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-foward consul-server-0 8500 &

If TLS is enabled use port 8501:

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

Be sure the latest consul binary is installed locally on your host. https://releases.hashicorp.com/consul/

$ 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 -o jsonpath={.data.token} | base64 -D)

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 the configuration entry for the terminating gateway
• Create intentions 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": "legacy_node",
  "Address": "example.com",
  "NodeMeta": {
    "external-node": "true",
    "external-probe": "true"
  },
  "Service": {
    "ID": "example-https",
    "Service": "example-https",
    "Port": 443
  }
}

Register the external service with Consul:

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

If ACLs and TLS are enabled :

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

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

The CLI command should be run with the -merge-policies, -merge-roles and -merge-service-identities so nothing is removed from the terminating gateway token

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

$ consul acl policy create -name "example-https-write-policy" -rules @write-policy.hcl

Now fetch the id of the terminating gateway token

$ consul acl token list | grep terminating-gateway-terminating-gateway-token

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

Create the configuration entry for the terminating gateway

Once the tokens have been updated, next write the Consul config entry for the terminating gateway:

Kind = "terminating-gateway"
Name = "terminating-gateway"
Services = [
 {
   Name = "example-https"
   CAFile = "/etc/ssl/cert.pem"
 }
]

If TLS is enabled a CAFile must be provided, it must point to the system trust store of the terminating gateway container.

Submit the terminating gateway entry with the Consul CLI using this command.

$ consul config write terminating-gateway.hcl

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

$ consul intention create -allow static-client example-https

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: 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:
        # This name will be the service name in Consul.
        - name: static-client
          image: tutum/curl:latest
          command: ['/bin/sh', '-c', '--']
          args: ['while true; do sleep 30; done;']
        # If ACLs are enabled, the serviceAccountName must match the Consul service name.
      serviceAccountName: static-client

Run the service via kubectl apply:

$ kubectl apply -f static-client.yaml

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

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