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Kubernetes Response Engine, Part 1: Falcosidekick + Kubeless

By Thomas Labarussias |

This blog post is part of a series of articles about how to create a Kubernetes response engine with Falco, Falcosidekick and a FaaS.

See other posts:

Two years ago, we presented to you a Kubernetes Response Engine based on Falco. The idea was to trigger Kubeless serverless functions for deleting infected pod, start a Sysdig capture or forward the events to GCP PubSub. See the README.

To avoid maintaining this custom stack, we worked hard with the community to integrate all components into Falcosidekick and to improve the UX. With the last release 2.20.0 we have the finale piece, the integration of Kubeless as native output. More details in our retrospective of 2020.

In this blog post, we will explain the basic concepts for integrating your own Response Engine into K8S with the stack Falco + Falcosidekick + Kubeless.

Requirements

We require a kubernetes cluster running at least 1.17 release and helm and kubectl installed.

Install Kubeless

Follow the official quick start page:

export RELEASE=$(curl -s https://api.github.com/repos/kubeless/kubeless/releases/latest | grep tag_name | cut -d '"' -f 4)
kubectl create ns kubeless
kubectl create -f https://github.com/kubeless/kubeless/releases/download/$RELEASE/kubeless-$RELEASE.yaml

After a few seconds, we can check that the controller is up and running:

kubectl get pods -n kubeless
NAME                                          READY   STATUS    RESTARTS   AGE
kubeless-controller-manager-99459cb67-tb99d   3/3     Running   3          2m34s

Install Falco

Firstly, we'll create the namespace that will use both Falco and Falcosidekick:

kubectl create ns falco

Add the helm repo:

helm repo add falcosecurity https://falcosecurity.github.io/charts

In a real project, you should get the whole chart with helm pull falcosecurity/falco --untar and then configure the values.yaml. For this tutorial, we will try to keep things as easy as possible and set configs directly by helm install command:

helm install falco falcosecurity/falco --set falco.jsonOutput=true --set falco.httpOutput.enabled=true --set falco.httpOutput.url=http://falcosidekick:2801 -n falco

You should get this output:

NAME: falco
LAST DEPLOYED: Thu Jan 14 23:43:46 2021
NAMESPACE: falco
STATUS: deployed
REVISION: 1
TEST SUITE: None
NOTES:
Falco agents are spinning up on each node in your cluster. After a few
seconds, they are going to start monitoring your containers looking for
security issues.
No further action should be required.

And you can see your new Falco pods:

kubectl get pods -n falco
NAME                           READY   STATUS        RESTARTS   AGE
falco-ctmzg                    1/1     Running       0          111s
falco-sfnn8                    1/1     Running       0          111s
falco-rrg28                    1/1     Running       0          111s

The arguments --set falco.jsonOutput=true --set falco.httpOutput.enabled=true --set falco.httpOutput.url=http://falcosidekick:2801 are there configuring the format of events and the URL where Falco will send them. As Falco and Falcosidekick will be in the same namespace, we can directly use the name of the service (falcosidekick).

Install Falcosidekick

The process is quite the same:

helm install falcosidekick falcosecurity/falcosidekick --set config.kubeless.namespace=kubeless --set config.kubeless.function=delete-pod -n falco

You should get this output:

NAME: falcosidekick
LAST DEPLOYED: Thu Jan 14 23:55:12 2021
NAMESPACE: falco
STATUS: deployed
REVISION: 1
NOTES:
1. Get the application URL by running these commands:
  export POD_NAME=$(kubectl get pods --namespace falco -l "app.kubernetes.io/name=falcosidekick,app.kubernetes.io/instance=falcosidekick" -o jsonpath="{.items[0].metadata.name}")
  kubectl port-forward $POD_NAME 2801:2801
  echo "Visit http://127.0.0.1:2801 to use your application"

We check the logs:

kubectl logs deployment/falcosidekick -n falco
2021/01/14 22:55:31 [INFO]  : Enabled Outputs : Kubeless
2021/01/14 22:55:31 [INFO]  : Falco Sidekick is up and listening on port 2801

Kubeless is displayed as enabled output, everything is good 👍.

That's it, we really tried to get a nice UX 😉.

Install our Kubeless function

We'll not explain how to write or how to work Kubeless functions, please read the official docs for more information.

Our basic function will receive events from Falco, thanks to Falcosidekick. Check if the triggered rule is Terminal Shell in container. See rule, extract the namespace and pod name from fields of events, and delete the according pod:

from kubernetes import client,config

config.load_incluster_config()

def delete_pod(event, context):
    rule = event['data']['rule'] or None
    output_fields = event['data']['output_fields'] or None

    if rule and rule == "Terminal shell in container" and output_fields:
        if output_fields['k8s.ns.name'] and output_fields['k8s.pod.name']:
            pod = output_fields['k8s.pod.name']
            namespace = output_fields['k8s.ns.name']
            print (f"Deleting pod \"{pod}\" in namespace \"{namespace}\"")
            client.CoreV1Api().delete_namespaced_pod(name=pod, namespace=namespace, body=client.V1DeleteOptions())

Basically, the process is:

           +----------+                 +---------------+                    +----------+
           |  Falco   +-----------------> Falcosidekick +--------------------> Kubeless |
           +----^-----+   sends event   +---------------+      triggers      +-----+----+
                |                                                                  |
detects a shell |                                                                  |
                |                                                                  |
           +----+-------+                                   deletes                |
           | Pwned Pod  <----------------------------------------------------------+
           +------------+

Before deploying our function, we need to create a ServiceAccount for it, as it will need the right to delete a pod in any namespace:

cat <<EOF | kubectl apply -n kubeless -f -
apiVersion: v1
kind: ServiceAccount
metadata:
  name: falco-pod-delete
---
kind: ClusterRole
apiVersion: rbac.authorization.k8s.io/v1
metadata:
  name: falco-pod-delete-cluster-role
rules:
  - apiGroups: [""]
    resources: ["pods"]
    verbs: ["get", "list", "delete"]
---
kind: ClusterRoleBinding
apiVersion: rbac.authorization.k8s.io/v1
metadata:
  name: falco-pod-delete-cluster-role-binding
roleRef:
  kind: ClusterRole
  name: falco-pod-delete-cluster-role
  apiGroup: rbac.authorization.k8s.io
subjects:
  - kind: ServiceAccount
    name: falco-pod-delete
    namespace: kubeless
EOF

namespace: kubelessetetion.k8s.io
serviceaccount/falco-pod-delete created
clusterrole.rbac.authorization.k8s.io/falco-pod-delete-cluster-role created
clusterrolebinding.rbac.authorization.k8s.io/falco-pod-delete-cluster-role-binding created

Only remains the installation of our function itself:

cat <<EOF | kubectl apply -n kubeless -f -
apiVersion: kubeless.io/v1beta1
kind: Function
metadata:
  finalizers:
    - kubeless.io/function
  generation: 1
  labels:
    created-by: kubeless
    function: delete-pod
  name: delete-pod
spec:
  checksum: sha256:a68bf570ea30e578e392eab18ca70dbece27bce850a8dbef2586eff55c5c7aa0
  deps: |
    kubernetes>=12.0.1
  function-content-type: text
  function: |-
    from kubernetes import client,config

    config.load_incluster_config()

    def delete_pod(event, context):
        rule = event['data']['rule'] or None
        output_fields = event['data']['output_fields'] or None

        if rule and rule == "Terminal shell in container" and output_fields:
            if output_fields['k8s.ns.name'] and output_fields['k8s.pod.name']:
                pod = output_fields['k8s.pod.name']
                namespace = output_fields['k8s.ns.name']
                print (f"Deleting pod \"{pod}\" in namespace \"{namespace}\"")
                client.CoreV1Api().delete_namespaced_pod(name=pod, namespace=namespace, body=client.V1DeleteOptions())
  handler: delete-pod.delete_pod
  runtime: python3.7
  deployment:
    spec:
      template:
        spec:
          serviceAccountName: falco-pod-delete
EOF

function.kubeless.io/delete-pod created

kubectl get pods -n kubeless

NAME                                          READY   STATUS    RESTARTS   AGE
kubeless-controller-manager-99459cb67-tb99d   3/3     Running   3          3d14h
delete-pod-d6f98f6dd-cw228                    1/1     Running   0          2m52s

kubectl get svc -n kubeless

NAME         TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)          AGE
delete-pod   ClusterIP   10.43.211.201   <none>        8080/TCP         4m38s

Test our function

We start by creating a dumb pod:

kubectl run alpine -n default --image=alpine --restart='Never' -- sh -c "sleep 600"

kubectl get pods -n default
NAME     READY   STATUS    RESTARTS   AGE
alpine   1/1     Running   0          9s

Let's run a shell command inside and see what happens:

kubectl exec -i --tty alpine -n default -- sh -c "uptime"

23:44:25 up 1 day, 19:11,  load average: 0.87, 0.77, 0.77

As expected, we got the result of our command, but, to get the status of the pod now:

kubectl get pods -n default
NAME     READY   STATUS        RESTARTS   AGE
alpine   1/1     Terminating   0          103s

💥 It has been terminated 💥

We can now check the logs of components.

For Falco:

kubectl logs daemonset/falco -n falco

{"output":"23:39:44.834631763: Notice A shell was spawned in a container with an attached terminal (user=root user_loginuid=-1 k8s.ns=default k8s.pod=alpine container=5892b41bcf46 shell=sh parent=<NA> cmdline=sh terminal=34817 container_id=5892b41bcf46 image=<NA>) k8s.ns=default k8s.pod=alpine container=5892b41bcf46","priority":"Notice","rule":"Terminal shell in container","time":"2021-01-14T23:39:44.834631763Z", "output_fields": {"container.id":"5892b41bcf46","container.image.repository":null,"evt.time":1610667584834631763,"k8s.ns.name":"default","k8s.pod.name":"alpine","proc.cmdline":"sh","proc.name":"sh","proc.pname":null,"proc.tty":34817,"user.loginuid":-1,"user.name":"root"}}

For Falcosidekick:

kubectl logs deployment/falcosidekick -n falco

2021/01/14 23:39:45 [INFO]  : Kubeless - Post OK (200)
2021/01/14 23:39:45 [INFO]  : Kubeless - Function Response :
2021/01/14 23:39:45 [INFO]  : Kubeless - Call Function "delete-pod" OK

(Notice, the function returns nothing, this is why the message log is empty)

For delete-pod function:

kubectl logs deployment/delete-pod -n kubeless

10.42.0.31 - - [14/Jan/2021:23:39:45 +0000] "POST / HTTP/1.1" 200 0 "" "Falcosidekick" 0/965744
Deleting pod "alpine" in namespace "default"

Conclusion

With this simple example, we only scratched the surface of possibilities. Everything is possible now, so don't hesitate to share with us on Slack (https://kubernetes.slack.com #falco) your comments, ideas and successes. You're always welcome to contribute.

Bonus: You're running Falcosidekick outside Kubernetes but still want to use the Kubeless output? No problem, you can declare a kubeconfig file to use. See README.

Bonus 2: For people who wants to use Knative in place of Kubeless, it's coming soon 😉

Enjoy