Egress using Wildcard Hosts
The Accessing External Services task and
the Configure an Egress Gateway example
describe how to configure egress traffic for specific hostnames, like edition.cnn.com
.
This example shows how to enable egress traffic for a set of hosts in a common domain, for
example *.wikipedia.org
, instead of configuring each and every host separately.
Background
Suppose you want to enable egress traffic in Istio for the wikipedia.org
sites in all languages.
Each version of wikipedia.org
in a particular language has its own hostname, e.g., en.wikipedia.org
and
de.wikipedia.org
in the English and the German languages, respectively.
You want to enable egress traffic by common configuration items for all the Wikipedia sites,
without the need to specify every language’s site separately.
Before you begin
Install Istio using the
demo
configuration profile and with the blocking-by-default outbound traffic policy:$ istioctl install --set profile=demo --set meshConfig.outboundTrafficPolicy.mode=REGISTRY_ONLY
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=$(kubectl get pod -l app=sleep -o jsonpath={.items..metadata.name})
Configure direct traffic to a wildcard host
The first, and simplest, way to access a set of hosts within a common domain is by configuring
a simple ServiceEntry
with a wildcard host and calling the services directly from the sidecar.
When calling services directly (i.e., not via an egress gateway), the configuration for
a wildcard host is no different than that of any other (e.g., fully qualified) host,
only much more convenient when there are many hosts within the common domain.
Define a
ServiceEntry
for*.wikipedia.org
:$ kubectl apply -f - <<EOF apiVersion: networking.istio.io/v1alpha3 kind: ServiceEntry metadata: name: wikipedia spec: hosts: - "*.wikipedia.org" ports: - number: 443 name: https protocol: HTTPS EOF
Send HTTPS requests to https://en.wikipedia.org and https://de.wikipedia.org:
$ kubectl exec "$SOURCE_POD" -c sleep -- sh -c 'curl -s https://en.wikipedia.org/wiki/Main_Page | grep -o "<title>.*</title>"; curl -s https://de.wikipedia.org/wiki/Wikipedia:Hauptseite | grep -o "<title>.*</title>"' <title>Wikipedia, the free encyclopedia</title> <title>Wikipedia – Die freie Enzyklopädie</title>
Cleanup direct traffic to a wildcard host
$ kubectl delete serviceentry wikipedia
Configure egress gateway traffic to a wildcard host
When all wildcard hosts are served by a single server, the configuration for egress gateway-based access to a wildcard host is very similar to that of any host, with one exception: the configured route destination will not be the same as the configured host, i.e., the wildcard. It will instead be configured with the host of the single server for the set of domains.
Create an egress
Gateway
for *.wikipedia.org, a destination rule and a virtual service to direct the traffic through the egress gateway and from the egress gateway to the external service.$ kubectl apply -f - <<EOF apiVersion: networking.istio.io/v1alpha3 kind: Gateway metadata: name: istio-egressgateway spec: selector: istio: egressgateway servers: - port: number: 443 name: https protocol: HTTPS hosts: - "*.wikipedia.org" tls: mode: PASSTHROUGH --- apiVersion: networking.istio.io/v1alpha3 kind: DestinationRule metadata: name: egressgateway-for-wikipedia spec: host: istio-egressgateway.istio-system.svc.cluster.local subsets: - name: wikipedia --- apiVersion: networking.istio.io/v1alpha3 kind: VirtualService metadata: name: direct-wikipedia-through-egress-gateway spec: hosts: - "*.wikipedia.org" gateways: - mesh - istio-egressgateway tls: - match: - gateways: - mesh port: 443 sniHosts: - "*.wikipedia.org" route: - destination: host: istio-egressgateway.istio-system.svc.cluster.local subset: wikipedia port: number: 443 weight: 100 - match: - gateways: - istio-egressgateway port: 443 sniHosts: - "*.wikipedia.org" route: - destination: host: www.wikipedia.org port: number: 443 weight: 100 EOF
Create a
ServiceEntry
for the destination server, www.wikipedia.org.$ kubectl apply -f - <<EOF apiVersion: networking.istio.io/v1alpha3 kind: ServiceEntry metadata: name: www-wikipedia spec: hosts: - www.wikipedia.org ports: - number: 443 name: https protocol: HTTPS resolution: DNS EOF
Send HTTPS requests to https://en.wikipedia.org and https://de.wikipedia.org:
$ kubectl exec "$SOURCE_POD" -c sleep -- sh -c 'curl -s https://en.wikipedia.org/wiki/Main_Page | grep -o "<title>.*</title>"; curl -s https://de.wikipedia.org/wiki/Wikipedia:Hauptseite | grep -o "<title>.*</title>"' <title>Wikipedia, the free encyclopedia</title> <title>Wikipedia – Die freie Enzyklopädie</title>
Check the statistics of the egress gateway’s proxy for the counter that corresponds to your requests to *.wikipedia.org. If Istio is deployed in the
istio-system
namespace, the command to print the counter is:$ kubectl exec "$(kubectl get pod -l istio=egressgateway -n istio-system -o jsonpath='{.items[0].metadata.name}')" -c istio-proxy -n istio-system -- pilot-agent request GET clusters | grep '^outbound|443||www.wikipedia.org.*cx_total:' outbound|443||www.wikipedia.org::208.80.154.224:443::cx_total::2
Cleanup egress gateway traffic to a wildcard host
$ kubectl delete serviceentry www-wikipedia
$ kubectl delete gateway istio-egressgateway
$ kubectl delete virtualservice direct-wikipedia-through-egress-gateway
$ kubectl delete destinationrule egressgateway-for-wikipedia
Wildcard configuration for arbitrary domains
The configuration in the previous section worked because all the *.wikipedia.org
sites can be served by any one
of the wikipedia.org
servers. However, this is not always the case. For example, you may want to configure egress
control for access to more general wildcard domains like *.com
or *.org
. Configuring traffic to arbitrary
wildcard domains introduces a challenge for Istio gateways; an Istio gateway can only be configured to route traffic
to predefined hosts, predefined IP addresses, or to the original destination IP address of the request.
In the previous section you configured the virtual service to direct traffic to the predefined host www.wikipedia.org
.
In the general case, however, you don’t know the host or IP address that can serve an arbitrary host received in a
request, which leaves the original destination address of the request as the only value with which to route the request.
Unfortunately, when using an egress gateway, the original destination address of the request is lost since the original
request is redirected to the gateway, causing the destination IP address to become the IP address of the gateway.
Although not as easy and somewhat fragile as it relies on Istio implementation details, you can use Envoy filters to configure a gateway to support arbitrary domains by using the SNI value in an HTTPS, or any TLS, request to identify the original destination to which to route the request. One example of this configuration approach can be found in routing egress traffic to wildcard destinations.
Cleanup
Shutdown the sleep service:
$ kubectl delete -f @samples/sleep/sleep.yaml@
Uninstall Istio from your cluster:
$ istioctl uninstall --purge -y