Harden the nodes with AppArmor and seccomp

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$ als gewone gebruiker# als root (of met sudo)

Vaardigheden in dit hoofdstuk

Klein host-OS, AppArmor, seccomp, IAM en netwerktoegang

Keep the host small

Every package, service and open port on a node is a possible way in.

#systemctl list-units --type=service --state=running
#ss -tulpn
#apt list --installed | wc -l
#systemctl disable --now snapd cups avahi-daemon
#echo "install dccp /bin/true" > /etc/modprobe.d/disable-dccp.conf

Use a minimal OS image (or a container-optimised OS).
No SSH passwords, no shared admin accounts.
Cloud IAM: the node's identity gets only the rights the kubelet needs.

3.2

Use AppArmor profiles

An AppArmor profile on the node says what a program may do. The pod asks for it in securityContext.appArmorProfile.

/etc/apparmor.d/k8s-deny-write

#include <tunables/global>
profile k8s-deny-write flags=(attach_disconnected) {
  #include <abstractions/base>
  file,
  deny /** w,
}

#apparmor_parser -q /etc/apparmor.d/k8s-deny-write
#aa-status | grep k8s-deny-write

pod-apparmor.yaml

apiVersion: v1
kind: Pod
metadata: { name: ro-app, namespace: shop }
spec:
  nodeName: worker1
  securityContext:
    appArmorProfile:
      type: Localhost
      localhostProfile: k8s-deny-write
  containers:
    - name: app
      image: busybox:1.36
      command: ["sh", "-c", "touch /tmp/x; sleep 3600"]

$kubectl logs ro-app -n shop
touch: /tmp/x: Permission denied

Onthoud

The profile must be loaded on the node where the pod runs — pin the pod (or load the profile on every node).

3.3

Use seccomp profiles

seccomp filters system calls. RuntimeDefault (the runtime's safe list) fits almost every app; custom profiles live in /var/lib/kubelet/seccomp/.

pod-seccomp.yaml

spec:
  securityContext:
    seccompProfile:
      type: RuntimeDefault
  containers:
    - name: app
      image: nginx:1.27
      securityContext:
        seccompProfile:
          type: Localhost
          localhostProfile: profiles/audit.json

/var/lib/kubelet/seccomp/profiles/audit.json

{ "defaultAction": "SCMP_ACT_LOG" }

Type	Meaning
`RuntimeDefault`	The container runtime's default filter
`Localhost`	A JSON profile on the node (path relative to the seccomp folder)
`Unconfined`	No filter — avoid

3.4

Restrict capabilities and privilege

Drop all Linux capabilities and add back only what the app needs.

container securityContext

securityContext:
  allowPrivilegeEscalation: false
  privileged: false
  capabilities:
    drop: ["ALL"]
    add: ["NET_BIND_SERVICE"]

Examentip

Read the task for the exact place: some settings are pod-level (spec.securityContext), some container-level (spec.containers[].securityContext) — capabilities and allowPrivilegeEscalation only exist per container.

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