Kubernetes Services for Egress Traffic
Kubernetes ExternalName
services and Kubernetes services with
Endpoints
let you create a local DNS alias to an external service.
This DNS alias has the same form as the DNS entries for local services, namely
<service name>.<namespace name>.svc.cluster.local
. DNS aliases provide location transparency for your workloads:
the workloads can call local and external services in the same way. If at some point in time you decide to deploy the
external service inside your cluster, you can just update its Kubernetes service to reference the local version. The workloads will continue to operate without any change.
This task shows that these Kubernetes mechanisms for accessing external services continue to work with Istio. The only configuration step you must perform is to use a TLS mode other than Istio’s mutual TLS. The external services are not part of an Istio service mesh so they cannot perform the mutual TLS of Istio. You must set the TLS mode according to the TLS requirements of the external service and according to the way your workload accesses the external service. If your workload issues plain HTTP requests and the external service requires TLS, you may want to perform TLS origination by Istio. If your workload already uses TLS, the traffic is already encrypted and you can just disable Istio’s mutual TLS.
While the examples in this task use HTTP protocols, Kubernetes Services for egress traffic work with other protocols as well.
Before you begin
Setup Istio by following the instructions in the Installation guide.
Deploy the sleep sample app to use as a test source for sending requests. If you have automatic sidecar injection enabled, run the following command to deploy the sample app:
$ kubectl apply -f @samples/sleep/sleep.yaml@
Otherwise, manually inject the sidecar before deploying the
sleep
application with the following command:$ kubectl apply -f <(istioctl kube-inject -f @samples/sleep/sleep.yaml@)
Set the
SOURCE_POD
environment variable to the name of your source pod:$ export SOURCE_POD=$(kubectl get pod -l app=sleep -o jsonpath={.items..metadata.name})
Create a namespace for a source pod without Istio control:
$ kubectl create namespace without-istio
Start the sleep sample in the
without-istio
namespace.$ kubectl apply -f @samples/sleep/sleep.yaml@ -n without-istio
To send requests, create the
SOURCE_POD_WITHOUT_ISTIO
environment variable to store the name of the source pod:$ export SOURCE_POD_WITHOUT_ISTIO="$(kubectl get pod -n without-istio -l app=sleep -o jsonpath={.items..metadata.name})"
Verify that the Istio sidecar was not injected, that is the pod has one container:
$ kubectl get pod "$SOURCE_POD_WITHOUT_ISTIO" -n without-istio NAME READY STATUS RESTARTS AGE sleep-66c8d79ff5-8tqrl 1/1 Running 0 32s
Kubernetes ExternalName service to access an external service
Create a Kubernetes ExternalName service for
httpbin.org
in the default namespace:$ kubectl apply -f - <<EOF kind: Service apiVersion: v1 metadata: name: my-httpbin spec: type: ExternalName externalName: httpbin.org ports: - name: http protocol: TCP port: 80 EOF
Observe your service. Note that it does not have a cluster IP.
$ kubectl get svc my-httpbin NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE my-httpbin ExternalName <none> httpbin.org 80/TCP 4s
Access
httpbin.org
via the Kubernetes service’s hostname from the source pod without Istio sidecar. Note that the curl command below uses the Kubernetes DNS format for services:<service name>.<namespace>.svc.cluster.local
.$ kubectl exec "$SOURCE_POD_WITHOUT_ISTIO" -n without-istio -c sleep -- curl -sS my-httpbin.default.svc.cluster.local/headers { "headers": { "Accept": "*/*", "Host": "my-httpbin.default.svc.cluster.local", "User-Agent": "curl/7.55.0" } }
In this example, unencrypted HTTP requests are sent to
httpbin.org
. For the sake of the example only, you disable the TLS mode and allow the unencrypted traffic to the external service. In the real life scenarios, we recommend to perform Egress TLS origination by Istio.$ kubectl apply -f - <<EOF apiVersion: networking.istio.io/v1 kind: DestinationRule metadata: name: my-httpbin spec: host: my-httpbin.default.svc.cluster.local trafficPolicy: tls: mode: DISABLE EOF
Access
httpbin.org
via the Kubernetes service’s hostname from the source pod with Istio sidecar. Notice the headers added by Istio sidecar, for exampleX-Envoy-Peer-Metadata
. Also note that theHost
header equals to your service’s hostname.$ kubectl exec "$SOURCE_POD" -c sleep -- curl -sS my-httpbin.default.svc.cluster.local/headers { "headers": { "Accept": "*/*", "Content-Length": "0", "Host": "my-httpbin.default.svc.cluster.local", "User-Agent": "curl/7.64.0", "X-B3-Sampled": "0", "X-B3-Spanid": "5795fab599dca0b8", "X-B3-Traceid": "5079ad3a4af418915795fab599dca0b8", "X-Envoy-Peer-Metadata": "...", "X-Envoy-Peer-Metadata-Id": "sidecar~10.28.1.74~sleep-6bdb595bcb-drr45.default~default.svc.cluster.local" } }
Cleanup of Kubernetes ExternalName service
$ kubectl delete destinationrule my-httpbin
$ kubectl delete service my-httpbin
Use a Kubernetes service with endpoints to access an external service
Create a Kubernetes service without selector for Wikipedia:
$ kubectl apply -f - <<EOF kind: Service apiVersion: v1 metadata: name: my-wikipedia spec: ports: - protocol: TCP port: 443 name: tls EOF
Create endpoints for your service. Pick a couple of IPs from the Wikipedia ranges list.
$ kubectl apply -f - <<EOF kind: Endpoints apiVersion: v1 metadata: name: my-wikipedia subsets: - addresses: - ip: 198.35.26.96 - ip: 208.80.153.224 ports: - port: 443 name: tls EOF
Observe your service. Note that it has a cluster IP which you can use to access
wikipedia.org
.$ kubectl get svc my-wikipedia NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE my-wikipedia ClusterIP 172.21.156.230 <none> 443/TCP 21h
Send HTTPS requests to
wikipedia.org
by your Kubernetes service’s cluster IP from the source pod without Istio sidecar. Use the--resolve
option ofcurl
to accesswikipedia.org
by the cluster IP:$ kubectl exec "$SOURCE_POD_WITHOUT_ISTIO" -n without-istio -c sleep -- curl -sS --resolve en.wikipedia.org:443:"$(kubectl get service my-wikipedia -o jsonpath='{.spec.clusterIP}')" https://en.wikipedia.org/wiki/Main_Page | grep -o "<title>.*</title>" <title>Wikipedia, the free encyclopedia</title>
In this case, the workload send HTTPS requests (open TLS connection) to the
wikipedia.org
. The traffic is already encrypted by the workload so you can safely disable Istio’s mutual TLS:$ kubectl apply -f - <<EOF apiVersion: networking.istio.io/v1 kind: DestinationRule metadata: name: my-wikipedia spec: host: my-wikipedia.default.svc.cluster.local trafficPolicy: tls: mode: DISABLE EOF
Access
wikipedia.org
by your Kubernetes service’s cluster IP from the source pod with Istio sidecar:$ kubectl exec "$SOURCE_POD" -c sleep -- curl -sS --resolve en.wikipedia.org:443:"$(kubectl get service my-wikipedia -o jsonpath='{.spec.clusterIP}')" https://en.wikipedia.org/wiki/Main_Page | grep -o "<title>.*</title>" <title>Wikipedia, the free encyclopedia</title>
Check that the access is indeed performed by the cluster IP. Notice the sentence
Connected to en.wikipedia.org (172.21.156.230)
in the output ofcurl -v
, it mentions the IP that was printed in the output of your service as the cluster IP.$ kubectl exec "$SOURCE_POD" -c sleep -- curl -sS -v --resolve en.wikipedia.org:443:"$(kubectl get service my-wikipedia -o jsonpath='{.spec.clusterIP}')" https://en.wikipedia.org/wiki/Main_Page -o /dev/null * Added en.wikipedia.org:443:172.21.156.230 to DNS cache * Hostname en.wikipedia.org was found in DNS cache * Trying 172.21.156.230... * TCP_NODELAY set * Connected to en.wikipedia.org (172.21.156.230) port 443 (#0) ...
Cleanup of Kubernetes service with endpoints
$ kubectl delete destinationrule my-wikipedia
$ kubectl delete endpoints my-wikipedia
$ kubectl delete service my-wikipedia
Cleanup
Shutdown the sleep service:
$ kubectl delete -f @samples/sleep/sleep.yaml@
Shutdown the sleep service in the
without-istio
namespace:$ kubectl delete -f @samples/sleep/sleep.yaml@ -n without-istio
Delete
without-istio
namespace:$ kubectl delete namespace without-istio
Unset the environment variables:
$ unset SOURCE_POD SOURCE_POD_WITHOUT_ISTIO