Egress TLS Origination
The Control Egress Traffic task demonstrates how external, i.e., outside of the
service mesh, HTTP and HTTPS services can be accessed from applications inside the mesh. As described in that task,
a ServiceEntry
is used to configure Istio
to access external services in a controlled way.
This example shows how to configure Istio to perform TLS origination
for traffic to an external service. Istio will open HTTPS connections to the external service while the original
traffic is HTTP.
Use case
Consider a legacy application that performs HTTP calls to external sites. Suppose the organization that operates the application receives a new requirement which states that all the external traffic must be encrypted. With Istio, this requirement can be achieved just by configuration, without changing any code in the application. The application can send unencrypted HTTP requests and Istio will then encrypt them for the application.
Another benefit of sending unencrypted HTTP requests from the source, and letting Istio perform the TLS upgrade, is that Istio can produce better telemetry and provide more routing control for requests that are not encrypted.
Before you begin
Setup Istio by following the instructions in the Installation guide.
Start the sleep sample which will be used as a test source for external calls.
If you have enabled automatic sidecar injection, deploy the
sleep
application:$ kubectl apply -f @samples/sleep/sleep.yaml@
Otherwise, you have to manually inject the sidecar before deploying the
sleep
application:$ kubectl apply -f <(istioctl kube-inject -f @samples/sleep/sleep.yaml@)
Note that any pod that you can
exec
andcurl
from will do for the procedures below.Create a shell variable to hold the name of the source pod for sending requests to external services. If you used the sleep sample, run:
$ export SOURCE_POD=$(kubectl get pod -l app=sleep -o jsonpath={.items..metadata.name})
Configuring access to an external service
First start by configuring access to an external service, edition.cnn.com
,
using the same technique shown in the Control Egress Traffic task.
This time, however, use a single ServiceEntry
to enable both HTTP and HTTPS access to the service.
Create a
ServiceEntry
andVirtualService
to enable access toedition.cnn.com
:$ kubectl apply -f - <<EOF apiVersion: networking.istio.io/v1alpha3 kind: ServiceEntry metadata: name: edition-cnn-com spec: hosts: - edition.cnn.com ports: - number: 80 name: http-port protocol: HTTP - number: 443 name: https-port protocol: HTTPS resolution: DNS --- apiVersion: networking.istio.io/v1alpha3 kind: VirtualService metadata: name: edition-cnn-com spec: hosts: - edition.cnn.com tls: - match: - port: 443 sniHosts: - edition.cnn.com route: - destination: host: edition.cnn.com port: number: 443 weight: 100 EOF
Make a request to the external HTTP service:
$ kubectl exec "${SOURCE_POD}" -c sleep -- curl -sL -o /dev/null -D - http://edition.cnn.com/politics HTTP/1.1 301 Moved Permanently ... location: https://edition.cnn.com/politics ... HTTP/2 200 ...
The output should be similar to the above (some details replaced by ellipsis).
Notice the -L
flag of curl which instructs curl to follow redirects.
In this case, the server returned a redirect response (301 Moved Permanently)
for the HTTP request to http://edition.cnn.com/politics
.
The redirect response instructs the client to send an additional request, this time using HTTPS, to https://edition.cnn.com/politics
.
For the second request, the server returned the requested content and a 200 OK status code.
Although the curl command handled the redirection transparently, there are two issues here.
The first issue is the redundant request, which doubles the latency of fetching the content of http://edition.cnn.com/politics
.
The second issue is that the path of the URL, politics in this case, is sent in clear text.
If there is an attacker who sniffs the communication between your application and edition.cnn.com
,
the attacker would know which specific topics of edition.cnn.com
the application fetched.
For privacy reasons, you might want to prevent such disclosure.
Both of these issues can be resolved by configuring Istio to perform TLS origination.
TLS origination for egress traffic
Redefine your
VirtualService
from the previous section to rewrite the HTTP request port and add aDestinationRule
to perform TLS origination.$ kubectl apply -f - <<EOF apiVersion: networking.istio.io/v1alpha3 kind: VirtualService metadata: name: edition-cnn-com spec: hosts: - edition.cnn.com http: - match: - port: 80 route: - destination: host: edition.cnn.com subset: tls-origination port: number: 443 --- apiVersion: networking.istio.io/v1alpha3 kind: DestinationRule metadata: name: edition-cnn-com spec: host: edition.cnn.com subsets: - name: tls-origination trafficPolicy: loadBalancer: simple: ROUND_ROBIN portLevelSettings: - port: number: 443 tls: mode: SIMPLE # initiates HTTPS when accessing edition.cnn.com EOF
As you can see, the
VirtualService
redirects HTTP requests on port 80 to port 443 where the correspondingDestinationRule
then performs the TLS origination.Send an HTTP request to
http://edition.cnn.com/politics
, as in the previous section:$ kubectl exec "${SOURCE_POD}" -c sleep -- curl -sL -o /dev/null -D - http://edition.cnn.com/politics HTTP/1.1 200 OK ...
This time you receive 200 OK as the first and the only response. Istio performed TLS origination for curl so the original HTTP request was forwarded to
edition.cnn.com
as HTTPS. The server returned the content directly, without the need for redirection. You eliminated the double round trip between the client and the server, and the request left the mesh encrypted, without disclosing the fact that your application fetched the politics section ofedition.cnn.com
.Note that you used the same command as in the previous section. For applications that access external services programmatically, the code does not need to be changed. You get the benefits of TLS origination by configuring Istio, without changing a line of code.
Note that the applications that used HTTPS to access the external service continue to work as before:
$ kubectl exec "${SOURCE_POD}" -c sleep -- curl -sL -o /dev/null -D - https://edition.cnn.com/politics HTTP/2 200 ...
Additional security considerations
Because the traffic between the application pod and the sidecar proxy on the local host is still unencrypted, an attacker that is able to penetrate the node of your application would still be able to see the unencrypted communication on the local network of the node. In some environments a strict security requirement might state that all the traffic must be encrypted, even on the local network of the nodes. With such a strict requirement, applications should use HTTPS (TLS) only. The TLS origination described in this example would not be sufficient.
Also note that even with HTTPS originated by the application, an attacker could know that requests to edition.cnn.com
are being sent by inspecting Server Name Indication (SNI).
The SNI field is sent unencrypted during the TLS handshake. Using HTTPS prevents the attackers from knowing specific
topics and articles but does not prevent an attackers from learning that edition.cnn.com
is accessed.
Cleanup
Remove the Istio configuration items you created:
$ kubectl delete serviceentry edition-cnn-com $ kubectl delete virtualservice edition-cnn-com $ kubectl delete destinationrule edition-cnn-com
Shutdown the sleep service:
$ kubectl delete -f @samples/sleep/sleep.yaml@