Services use selectors to match the pods to direct the traffic. However, sometimes you need to implement a proxy to be the bridge between the Kubernetes cluster and another namespace, another cluster, or an external resource. In the following example, we'll demonstrate how to implement a proxy for http://www.google.com in your cluster. This is just an example; the source of the proxy in your case might be the endpoint of your database or another resource in the cloud:
The configuration file is similar to the previous one, just without the selector section:
// create a service without selectors
# cat 3-2-3_service_wo_selector_srv.yaml
kind: Service
apiVersion: v1
metadata:
name: google-proxy
spec:
ports:
- protocol: TCP
port: 80
targetPort: 80 // create service without selectors
# kubectl create -f 3-2-3_service_wo_selector_srv.yaml
service "google-proxy" created
No Kubernetes endpoint will be created, since there's no selector. Kubernetes doesn't know where to route the traffic, since no selector can match the pods. We'll have to create the endpoints manually.
In the Endpoints object, the source addresses can't be the DNS name, so we'll use nslookup to find the current Google IP from the domain, and add it to Endpoints.subsets.addresses.ip:
// get an IP from google.com
# nslookup www.google.com
Server: 192.168.1.1
Address: 192.168.1.1#53 Non-authoritative answer:
Name: google.com
Address: 172.217.0.238
// create endpoints for the ip from google.com
# cat 3-2-3_service_wo_selector_endpoints.yaml
kind: Endpoints
apiVersion: v1
metadata:
name: google-proxy
subsets:
- addresses:
- ip: 172.217.0.238
ports:
- port: 80 // create Endpoints
# kubectl create -f 3-2-3_service_wo_selector_endpoints.yaml
endpoints "google-proxy" created
Let's create another pod in the cluster to access our Google proxy:
// pod for accessing google proxy
# cat 3-2-3_proxy-chk.yaml
apiVersion: v1
kind: Pod
metadata:
name: proxy-chk
spec:
containers:
- name: centos
image: centos
command: ["/bin/sh", "-c", "while : ;do curl -L http://${GOOGLE_PROXY_SERVICE_HOST}:80/; sleep 10; done"]
// create the pod
# kubectl create -f 3-2-3_proxy-chk.yaml
pod "proxy-chk" created
Let's check stdout from the pod:
// get logs from proxy-chk
# kubectl logs proxy-chk
% Total % Received % Xferd Average Speed Time Time Time Current Dload Upload Total Spent Left Speed
100 219 100 219 0 0 2596 0 --:--:-- --:--:-- --:--:-- 2607
100 258 100 258 0 0 1931 0 --:--:-- --:--:-- --:--:-- 1931
<!doctype html><html itemscope="" itemtype="http://schema.org/WebPage" lang="en-CA">
...
Hurray! We can now confirm that the proxy works. The traffic to the Service will be routed to the endpoints we specified. If it doesn't work, make sure you add the proper inbound rules to the network of your external resources.
Endpoints don't support DNS as a source. Alternatively, we can use the ExternalName, which doesn't have selectors either. This requires kube-dns version >= 1.7.