UDP Routing

The UDPRoute resource allows users to configure UDP routing by matching UDP traffic and forwarding it to Kubernetes backends. This task will use CoreDNS example to walk you through the steps required to configure UDPRoute on Envoy Gateway.

Note: UDPRoute allows Envoy Gateway to operate as a non-transparent proxy between a UDP client and server. The lack of transparency means that the upstream server will see the source IP and port of the Gateway instead of the client. For additional information, refer to Envoy’s UDP proxy documentation.

Prerequisites

Follow the steps below to install Envoy Gateway and the example manifest. Before proceeding, you should be able to query the example backend using HTTP.

Installation

Install CoreDNS in the Kubernetes cluster as the example backend. The installed CoreDNS is listening on UDP port 53 for DNS lookups.

kubectl apply -f https://raw.githubusercontent.com/envoyproxy/gateway/latest/examples/kubernetes/udp-routing-example-backend.yaml

Wait for the CoreDNS deployment to become available:

kubectl wait --timeout=5m deployment/coredns --for=condition=Available

Update the Gateway from the Quickstart to include a UDP listener that listens on UDP port 5300:

kubectl patch gateway eg --type=json --patch '
  - op: add
    path: /spec/listeners/-
    value:
      name: coredns
      protocol: UDP
      port: 5300
      allowedRoutes:
        kinds:
        - kind: UDPRoute
  '

Verify the Gateway status:

kubectl get gateway/eg -o yaml

Configuration

Create a UDPRoute resource to route UDP traffic received on Gateway port 5300 to the CoredDNS backend.

• Apply from stdin
• Apply from file

cat <<EOF | kubectl apply -f -
apiVersion: gateway.networking.k8s.io/v1alpha2
kind: UDPRoute
metadata:
  name: coredns
spec:
  parentRefs:
    - name: eg
      sectionName: coredns
  rules:
    - backendRefs:
        - name: coredns
          port: 53
EOF

---
apiVersion: gateway.networking.k8s.io/v1alpha2
kind: UDPRoute
metadata:
  name: coredns
spec:
  parentRefs:
    - name: eg
      sectionName: coredns
  rules:
    - backendRefs:
        - name: coredns
          port: 53

Verify the UDPRoute status:

kubectl get udproute/coredns -o yaml

Testing

Get the External IP of the Gateway:

export GATEWAY_HOST=$(kubectl get gateway/eg -o jsonpath='{.status.addresses[0].value}')

Use dig command to query the dns entry foo.bar.com through the Gateway.

dig @${GATEWAY_HOST} -p 5300 foo.bar.com

You should see the result of the dns query as the below output, which means that the dns query has been successfully routed to the backend CoreDNS.

Note: 49.51.177.138 is the resolved address of GATEWAY_HOST.

; <<>> DiG 9.18.1-1ubuntu1.1-Ubuntu <<>> @49.51.177.138 -p 5300 foo.bar.com
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 58125
;; flags: qr aa rd; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 3
;; WARNING: recursion requested but not available

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1232
; COOKIE: 24fb86eba96ebf62 (echoed)
;; QUESTION SECTION:
;foo.bar.com.			IN	A

;; ADDITIONAL SECTION:
foo.bar.com.		0	IN	A	10.244.0.19
_udp.foo.bar.com.	0	IN	SRV	0 0 42376 .

;; Query time: 1 msec
;; SERVER: 49.51.177.138#5300(49.51.177.138) (UDP)
;; WHEN: Fri Jan 13 10:20:34 UTC 2023
;; MSG SIZE  rcvd: 114

Clean-Up

Follow the steps from the Quickstart to uninstall Envoy Gateway.

Delete the CoreDNS example manifest and the UDPRoute:

kubectl delete deploy/coredns
kubectl delete service/coredns
kubectl delete cm/coredns
kubectl delete udproute/coredns

Next Steps

Checkout the Developer Guide to get involved in the project.