Terminating Gateways on Kubernetes

1.9.0+: This feature is available in Consul versions 1.9.0 and higher

This topic requires familiarity with Terminating Gateways.

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:

  1. global:
  2.   name: consul
  3. connectInject:
  4.   enabled: true
  5. controller:
  6.   enabled: true
  7. terminatingGateways:
  8.   enabled: true

Terminating Gateways - 图1

config.yaml

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.

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

If TLS is enabled use port 8501:

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

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

  1. $ export CONSUL_HTTP_ADDR=http://localhost:8500

If TLS is enabled set:

  1. $ export CONSUL_HTTP_ADDR=https://localhost:8501
  2. $ export CONSUL_HTTP_SSL_VERIFY=false

If ACLs are enabled also set:

  1. $ 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

Note: Normal Consul services are registered with the Consul client on the node that they’re running on. Since this is an external service, there is no Consul node to register it onto. Instead, we will make up a node name and register the service to that node.

Create a sample external service and register it with Consul.

  1. {
  2.   "Node": "example_com",
  3.   "Address": "example.com",
  4.   "NodeMeta": {
  5.     "external-node": "true",
  6.     "external-probe": "true"
  7.   },
  8.   "Service": {
  9.     "Address": "example.com",
  10.     "ID": "example-https",
  11.     "Service": "example-https",
  12.     "Port": 443
  13.   }
  14. }

Terminating Gateways - 图2

external.json

  • “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:

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

If ACLs and TLS are enabled :

  1. $ curl --request PUT --header "X-Consul-Token: $CONSUL_HTTP_TOKEN" --data @external.json --insecure $CONSUL_HTTP_ADDR/v1/catalog/register
  2. 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

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

  1. service "example-https" {
  2.   policy = "write"
  3. }

Terminating Gateways - 图3

write-policy.hcl

  1. $ consul acl policy create -name "example-https-write-policy" -rules @write-policy.hcl
  2. ID:           xxxxxxxxxxxxxxx
  3. Name:         example-https-write-policy
  4. Description:
  5. Datacenters:
  6. Rules:
  7. service "example-https" {
  8.   policy = "write"
  9. }

Now fetch the ID of the terminating gateway token

  1. consul acl token list | grep -B 6 -- "- terminating-gateway-terminating-gateway-token" | grep AccessorID
  3. AccessorID:       <token id>

Update the terminating gateway acl token with the new policy

  1. $ consul acl token update -id <token-id> -policy-name example-https-write-policy -merge-policies -merge-roles -merge-service-identities
  2. AccessorID:       <token id>
  3. SecretID:         <secret id>
  4. Description:      terminating-gateway-terminating-gateway-token Token
  5. Local:            true
  6. Create Time:      2021-01-08 21:18:47.957450486 +0000 UTC
  7. Policies:
  8.    63bf1d9b-a87d-8672-ddcb-d25e2d88adb8 - terminating-gateway-terminating-gateway-token
  9.    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:

  1. apiVersion: consul.hashicorp.com/v1alpha1
  2. kind: TerminatingGateway
  3. metadata:
  4.   name: terminating-gateway
  5. spec:
  6.   services:
  7.     - name: example-https
  8.       caFile: /etc/ssl/cert.pem

Terminating Gateways - 图4

terminating-gateway.yaml

If TLS is enabled a caFile must be provided, it must point to the system trust store of the terminating gateway container (/etc/ssl/cert.pem).

Apply the TerminatingGateway resource with kubectl apply:

  1. $ 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

  1. apiVersion: consul.hashicorp.com/v1alpha1
  2. kind: ServiceIntentions
  3. metadata:
  4.   name: example-https
  5. spec:
  6.   destination:
  7.     name: example-https
  8.   sources:
  9.     - name: static-client
  10.       action: allow

Terminating Gateways - 图5

service-intentions.yaml

Apply the ServiceIntentions resource with kubectl apply:

  1. $ 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.

  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': 'example-https: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

Terminating Gateways - 图6

static-client.yaml

Run the service via kubectl apply:

  1. $ kubectl apply --filename static-client.yaml

Wait for the service to be ready:

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

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

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