Enforce Calico network policy using Istio (tutorial)
This tutorial sets up a microservices application, then demonstrates how to use Calico application layer policy to mitigate some common threats.
Note: This tutorial was verified using Istio v1.10.2. Some content may not apply to the latest Istio version.
- Build a Kubernetes cluster.
- Install Calico on Kubernetes:
- Install the calicoctl command line tool. Note: Ensure calicoctl is configured to connect with your datastore.
- Enable application layer policy.
Note: Label the default namespace for the Istio sidecar injection (
kubectl label namespace default istio-injection=enabled
Install the demo application
We will use a simple microservice application to demonstrate Calico application layer policy. The YAO Bank application creates a customer-facing web application, a microservice that serves up account summaries, and an etcd datastore.
kubectl apply -f https://projectcalico.docs.tigera.io/security/tutorials/app-layer-policy/manifests/10-yaobank.yaml
Note: You can also view the manifest in your browser.
Verify that the application pods have been created and are ready.
kubectl get pods
When the demo application has come up, you will see three pods.
Determining ingress IP and port
You will use the
istio-ingressgateway service to access the YAO Bank
application. Determine your ingress host and port following the Istio instructions. Once you have the
INGRESS_PORT variables set, you can
GATEWAY_URL as follows.
Point your browser to
http://$GATEWAY_URL/ to confirm the YAO Bank application is functioning
correctly. It may take several minutes for all the services to come up and respond, during which
time you may see 404 or 500 errors.
The need for policy
Although Calico & Istio are running in the cluster, we have not defined any authentication policy. Istio was configured to mutually authenticate traffic between the pods in your application, so only connections with Istio-issued certificates are allowed, and all inter-pod traffic is encrypted with TLS. That’s already a big step in the right direction.
But, let’s consider some deficiencies in this security architecture:
- All incoming connections from workloads in the Istio mesh are equally trusted
- Possession of a key & certificate pair is the only access credential considered.
To understand why these might be a problem, let’s take them one at a time.
Trusting connections from any workload in the Istio mesh is a poor security architecture because, like Kubernetes, Istio is designed to host multiple applications. Some of those applications may not be as trusted as others. They may be operated by different users or teams with wildly different security requirements. We don’t want our secure financial application microservices accessible from some hacky prototype another developer is cooking up.
Even within our own application, the best practice is to limit access as much as possible. Only pods that need access to a service should get it. Consider the YAO Bank application. The customer web service does not need, and should not have direct access to the backend database. The customer web service needs to directly interact with clients outside the cluster, some of whom may be malicious. Unfortunately, vulnerabilities in web applications are all too common. For example, an unpatched vulnerability in Apache Struts is what allowed attackers their initial access into the Equifax network where they then launched a devastating attack to steal millions of people’s financial information.
Imagine what would happen if an attacker were to gain control of the customer web pod in our application. Let’s simulate this by executing a remote shell inside that pod.
kubectl exec -ti customer-<fill in pod ID> -c customer -- bash
Notice that from here, we get direct access to the backend database. For example, we can list all the entries in the database like this:
curl http://database:2379/v2/keys?recursive=true | python -m json.tool
python -m json.tool nicely formats the output.)
The possession of a key and certificate pair is a very strong assertion that a connection is authentic because it is based on cryptographic proofs that are believed to be nearly impossible to forge. When we authenticate connections this way we can say with extremely high confidence that the party on the other end is in possession of the corresponding key. However, this is only a proxy for what we actually want to be confident of: that the party on the other end really is the authorized workload we want to communicate with. Keeping the private key a secret is vital to this confidence, and occasionally attackers can find ways to trick applications into giving up secrets they should not. For example, the Heartbleed vulnerability in OpenSSL allowed attackers to trick an affected application into reading out portions of its memory, compromising private keys.
We can mitigate both of the above deficiencies with a Calico policy.
wget https://projectcalico.docs.tigera.io/security/tutorials/app-layer-policy/manifests/30-policy.yaml calicoctl create -f 30-policy.yaml
Note: You can also view the manifest in your browser.
Let’s examine this policy piece by piece. It consists of three policy objects, one for each microservice.
This policy protects the customer web app. Since this application is customer facing, we do not
restrict what can communicate with it. We do, however, restrict its communications to HTTP
The second policy protects the account summary microservice. We know the only consumer of this service is the customer web app, so we restrict the source of incoming connections to the service account for the customer web app.
The third policy protects the database. Only the summary microservice should have direct access to the database.
Let’s verify our policy is working as intended. First, return to your browser and refresh to ensure policy enforcement has not broken the application.
Next, return to the customer web app. Recall that we simulated an attacker gaining control of that pod by executing a remote shell inside it.
kubectl exec -ti customer-<fill in pod ID> -c customer bash
Repeat our attempt to access the database.
curl -I http://database:2379/v2/keys?recursive=true
We have left out the JSON formatting because we do not expect to get a valid JSON response. This
time we should get a
403 Forbidden response. Only the account summary microservice has database
access according to our policy.