Egress TLS Origination
The Accessing External Services 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=$(kubectl get pod -l app=sleep -o jsonpath={.items..metadata.name})
Configuring access to an external service
First start by configuring access to an external service, edition.cnn.com
,
using the same technique shown in the Accessing External Services task.
This time, however, use a single ServiceEntry
to enable both HTTP and HTTPS access to the service.
Create a
ServiceEntry
to enable access toedition.cnn.com
:$ 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 EOF
Make a request to the external HTTP service:
$ kubectl exec "${SOURCE_POD}" -c sleep -- curl -sSL -o /dev/null -D - http://edition.cnn.com/politics HTTP/1.1 301 Moved Permanently ... location: https://edition.cnn.com/politics ... HTTP/2 200 ...
The output should be similar to the above (some details replaced by ellipsis).
Notice the -L
flag of curl which instructs curl to follow redirects.
In this case, the server returned a redirect response (301 Moved Permanently)
for the HTTP request to http://edition.cnn.com/politics
.
The redirect response instructs the client to send an additional request, this time using HTTPS, to https://edition.cnn.com/politics
.
For the second request, the server returned the requested content and a 200 OK status code.
Although the curl command handled the redirection transparently, there are two issues here.
The first issue is the redundant request, which doubles the latency of fetching the content of http://edition.cnn.com/politics
.
The second issue is that the path of the URL, politics in this case, is sent in clear text.
If there is an attacker who sniffs the communication between your application and edition.cnn.com
,
the attacker would know which specific topics of edition.cnn.com
the application fetched.
For privacy reasons, you might want to prevent such disclosure.
Both of these issues can be resolved by configuring Istio to perform TLS origination.
TLS origination for egress traffic
Redefine your
ServiceEntry
from the previous section to redirect HTTP requests to port 443 and add aDestinationRule
to perform TLS origination:$ 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 targetPort: 443 - number: 443 name: https-port protocol: HTTPS resolution: DNS --- apiVersion: networking.istio.io/v1alpha3 kind: DestinationRule metadata: name: edition-cnn-com spec: host: edition.cnn.com trafficPolicy: portLevelSettings: - port: number: 80 tls: mode: SIMPLE # initiates HTTPS when accessing edition.cnn.com EOF
The above
DestinationRule
will perform TLS origination for HTTP requests on port 80 and theServiceEntry
will then redirect the requests on port 80 to target port 443.Send an HTTP request to
http://edition.cnn.com/politics
, as in the previous section:$ kubectl exec "${SOURCE_POD}" -c sleep -- curl -sSL -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 -sSL -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 attackers from learning that edition.cnn.com
is accessed.
Cleanup the TLS origination configuration
Remove the Istio configuration items you created:
$ kubectl delete serviceentry edition-cnn-com
$ kubectl delete destinationrule edition-cnn-com
Mutual TLS origination for egress traffic
This section describes how to configure a sidecar to perform TLS origination for an external service, this time using a service that requires mutual TLS. This example is considerably more involved because it requires the following setup:
- Generate client and server certificates
- Deploy an external service that supports the mutual TLS protocol
- Configure the client (sleep pod) to use the credentials created in Step 1
Once this setup is complete, you can then configure the external traffic to go through the sidecar which will perform TLS origination.
Generate client and server certificates and keys
For this task you can use your favorite tool to generate certificates and keys. The commands below use openssl
Create a root certificate and private key to sign the certificate for your services:
$ openssl req -x509 -sha256 -nodes -days 365 -newkey rsa:2048 -subj '/O=example Inc./CN=example.com' -keyout example.com.key -out example.com.crt
Create a certificate and a private key for
my-nginx.mesh-external.svc.cluster.local
:$ openssl req -out my-nginx.mesh-external.svc.cluster.local.csr -newkey rsa:2048 -nodes -keyout my-nginx.mesh-external.svc.cluster.local.key -subj "/CN=my-nginx.mesh-external.svc.cluster.local/O=some organization" $ openssl x509 -req -sha256 -days 365 -CA example.com.crt -CAkey example.com.key -set_serial 0 -in my-nginx.mesh-external.svc.cluster.local.csr -out my-nginx.mesh-external.svc.cluster.local.crt
Optionally, you can add
SubjectAltNames
to the certificate if you want to enable SAN validation for the destination. For example:$ cat > san.conf <<EOF [req] distinguished_name = req_distinguished_name req_extensions = v3_req x509_extensions = v3_req prompt = no [req_distinguished_name] countryName = US [v3_req] keyUsage = critical, digitalSignature, keyEncipherment extendedKeyUsage = serverAuth, clientAuth basicConstraints = critical, CA:FALSE subjectAltName = critical, @alt_names [alt_names] DNS = my-nginx.mesh-external.svc.cluster.local EOF $ $ openssl req -out my-nginx.mesh-external.svc.cluster.local.csr -newkey rsa:4096 -nodes -keyout my-nginx.mesh-external.svc.cluster.local.key -subj "/CN=my-nginx.mesh-external.svc.cluster.local/O=some organization" -config san.conf $ openssl x509 -req -sha256 -days 365 -CA example.com.crt -CAkey example.com.key -set_serial 0 -in my-nginx.mesh-external.svc.cluster.local.csr -out my-nginx.mesh-external.svc.cluster.local.crt -extfile san.conf -extensions v3_req
Generate client certificate and private key:
$ openssl req -out client.example.com.csr -newkey rsa:2048 -nodes -keyout client.example.com.key -subj "/CN=client.example.com/O=client organization" $ openssl x509 -req -sha256 -days 365 -CA example.com.crt -CAkey example.com.key -set_serial 1 -in client.example.com.csr -out client.example.com.crt
Deploy a mutual TLS server
To simulate an actual external service that supports the mutual TLS protocol, deploy an NGINX server in your Kubernetes cluster, but running outside of the Istio service mesh, i.e., in a namespace without Istio sidecar proxy injection enabled.
Create a namespace to represent services outside the Istio mesh, namely
mesh-external
. Note that the sidecar proxy will not be automatically injected into the pods in this namespace since the automatic sidecar injection was not enabled on it.$ kubectl create namespace mesh-external
Create Kubernetes Secrets to hold the server’s and CA certificates.
$ kubectl create -n mesh-external secret tls nginx-server-certs --key my-nginx.mesh-external.svc.cluster.local.key --cert my-nginx.mesh-external.svc.cluster.local.crt $ kubectl create -n mesh-external secret generic nginx-ca-certs --from-file=example.com.crt
Create a configuration file for the NGINX server:
$ cat <<\EOF > ./nginx.conf events { } http { log_format main '$remote_addr - $remote_user [$time_local] $status ' '"$request" $body_bytes_sent "$http_referer" ' '"$http_user_agent" "$http_x_forwarded_for"'; access_log /var/log/nginx/access.log main; error_log /var/log/nginx/error.log; server { listen 443 ssl; root /usr/share/nginx/html; index index.html; server_name my-nginx.mesh-external.svc.cluster.local; ssl_certificate /etc/nginx-server-certs/tls.crt; ssl_certificate_key /etc/nginx-server-certs/tls.key; ssl_client_certificate /etc/nginx-ca-certs/example.com.crt; ssl_verify_client on; } } EOF
Create a Kubernetes ConfigMap to hold the configuration of the NGINX server:
$ kubectl create configmap nginx-configmap -n mesh-external --from-file=nginx.conf=./nginx.conf
Deploy the NGINX server:
$ kubectl apply -f - <<EOF apiVersion: v1 kind: Service metadata: name: my-nginx namespace: mesh-external labels: run: my-nginx annotations: "networking.istio.io/exportTo": "." # simulate an external service by not exporting outside this namespace spec: ports: - port: 443 protocol: TCP selector: run: my-nginx --- apiVersion: apps/v1 kind: Deployment metadata: name: my-nginx namespace: mesh-external spec: selector: matchLabels: run: my-nginx replicas: 1 template: metadata: labels: run: my-nginx spec: containers: - name: my-nginx image: nginx ports: - containerPort: 443 volumeMounts: - name: nginx-config mountPath: /etc/nginx readOnly: true - name: nginx-server-certs mountPath: /etc/nginx-server-certs readOnly: true - name: nginx-ca-certs mountPath: /etc/nginx-ca-certs readOnly: true volumes: - name: nginx-config configMap: name: nginx-configmap - name: nginx-server-certs secret: secretName: nginx-server-certs - name: nginx-ca-certs secret: secretName: nginx-ca-certs EOF
Configure the client (sleep pod)
Create Kubernetes Secrets to hold the client’s certificates:
$ kubectl create secret generic client-credential --from-file=tls.key=client.example.com.key \ --from-file=tls.crt=client.example.com.crt --from-file=ca.crt=example.com.crt
The secret must be created in the same namespace as the client pod is deployed in,
default
in this case.Create required
RBAC
to make sure the secret created in the above step is accessible to the client pod, which issleep
in this case.$ kubectl create role client-credential-role --resource=secret --verb=list $ kubectl create rolebinding client-credential-role-binding --role=client-credential-role --serviceaccount=default:sleep
Configure mutual TLS origination for egress traffic at sidecar
Add a
ServiceEntry
to redirect HTTP requests to port 443 and add aDestinationRule
to perform mutual TLS origination:$ kubectl apply -f - <<EOF apiVersion: networking.istio.io/v1alpha3 kind: ServiceEntry metadata: name: originate-mtls-for-nginx spec: hosts: - my-nginx.mesh-external.svc.cluster.local ports: - number: 80 name: http-port protocol: HTTP targetPort: 443 - number: 443 name: https-port protocol: HTTPS resolution: DNS --- apiVersion: networking.istio.io/v1alpha3 kind: DestinationRule metadata: name: originate-mtls-for-nginx spec: workloadSelector: matchLabels: app: sleep host: my-nginx.mesh-external.svc.cluster.local trafficPolicy: loadBalancer: simple: ROUND_ROBIN portLevelSettings: - port: number: 80 tls: mode: MUTUAL credentialName: client-credential # this must match the secret created earlier to hold client certs, and works only when DR has a workloadSelector sni: my-nginx.mesh-external.svc.cluster.local # this is optional EOF
The above
DestinationRule
will perform mTLS origination for HTTP requests on port 80 and theServiceEntry
will then redirect the requests on port 80 to target port 443.Verify that the credential is supplied to the sidecar and active.
$ istioctl proxy-config secret deploy/sleep | grep client-credential kubernetes://client-credential Cert Chain ACTIVE true 1 2024-06-04T12:15:20Z 2023-06-05T12:15:20Z kubernetes://client-credential-cacert Cert Chain ACTIVE true 10792363984292733914 2024-06-04T12:15:19Z 2023-06-05T12:15:19Z
Send an HTTP request to
http://my-nginx.mesh-external.svc.cluster.local
:$ kubectl exec "$(kubectl get pod -l app=sleep -o jsonpath={.items..metadata.name})" -c sleep -- curl -sS http://my-nginx.mesh-external.svc.cluster.local <!DOCTYPE html> <html> <head> <title>Welcome to nginx!</title> ...
Check the log of the
sleep
pod for a line corresponding to our request.$ kubectl logs -l app=sleep -c istio-proxy | grep 'my-nginx.mesh-external.svc.cluster.local'
You should see a line similar to the following:
[2022-05-19T10:01:06.795Z] "GET / HTTP/1.1" 200 - via_upstream - "-" 0 615 1 0 "-" "curl/7.83.1-DEV" "96e8d8a7-92ce-9939-aa47-9f5f530a69fb" "my-nginx.mesh-external.svc.cluster.local:443" "10.107.176.65:443"
Cleanup the mutual TLS origination configuration
Remove created Kubernetes resources:
$ kubectl delete secret nginx-server-certs nginx-ca-certs -n mesh-external $ kubectl delete secret client-credential $ kubectl delete rolebinding client-credential-role-binding $ kubectl delete role client-credential-role $ kubectl delete configmap nginx-configmap -n mesh-external $ kubectl delete service my-nginx -n mesh-external $ kubectl delete deployment my-nginx -n mesh-external $ kubectl delete namespace mesh-external $ kubectl delete serviceentry originate-mtls-for-nginx $ kubectl delete destinationrule originate-mtls-for-nginx
Delete the certificates and private keys:
$ rm example.com.crt example.com.key my-nginx.mesh-external.svc.cluster.local.crt my-nginx.mesh-external.svc.cluster.local.key my-nginx.mesh-external.svc.cluster.local.csr client.example.com.crt client.example.com.csr client.example.com.key
Delete the generated configuration files used in this example:
$ rm ./nginx.conf
Cleanup common configuration
Delete the sleep
service and deployment:
$ kubectl delete service sleep
$ kubectl delete deployment sleep