Kubernetes is becoming the operating system of the cloud. It manages workloads across clusters, orchestrating applications with efficiency and scale. But with great power comes great risk. If we don’t secure the container runtime, attackers can exploit vulnerabilities, steal data, or disrupt services. Threats lurk in outdated software, misconfigured permissions, and unchecked resource consumption. To keep our clusters safe, we must adopt strong security practices. Let’s explore the key strategies to protect our Kubernetes container runtime.
1. Update and Patch Regularly
Every software has flaws. Hackers search for these weaknesses, exploiting them to gain unauthorized access or disrupt operations. Containers are no exception. Critical vulnerabilities like CVE-2019-5736 in runc allowed attackers to escape the container and gain control over the host. If we don’t update Kubernetes and container runtimes, we leave doors open for such threats. We must apply patches quickly.2. Use Security Contexts
Containers should run with the least privileges necessary. By default, they may have more power than they need. We can set security contexts to:- Run containers as non-root users.
- Drop unnecessary Linux capabilities.
- Restrict privilege escalation.
apiVersion: v1
kind: Pod
metadata:
name: my-pod
spec:
securityContext:
runAsUser: 1000
runAsGroup: 3000
containers:
- name: my-container
image: my-image3. Use Read-Only Filesystems
A writable filesystem lets attackers plant malware or change configurations. Instead, we mount read-only filesystems where possible. This prevents unauthorized modifications and keeps our workloads safer.Example:
apiVersion: v1
kind: Pod
metadata:
name: my-pod
spec:
containers:
- name: my-container
image: my-image
securityContext:
readOnlyRootFilesystem: true4. Limit Resource Usage
Attackers often try to overwhelm systems with excessive CPU or memory usage, leading to Denial-of-Service (DoS) attacks. If one container uses too many resources, it can crash the entire node or degrade performance for other workloads. We prevent this by setting resource requests and limits in Kubernetes.Example:
apiVersion: v1
kind: Pod
metadata:
name: my-pod
spec:
containers:
- name: my-container
image: my-image
resources:
requests:
cpu: "100m"
memory: "200Mi"
limits:
cpu: "500m"
memory: "500Mi"5. Use Security Profiles
Linux security modules like SELinux and AppArmor provide extra protection. They define what a container can or cannot do. These tools block unauthorized access, preventing attackers from gaining deeper control.Example - Using SELinux
apiVersion: v1
kind: Pod
metadata:
name: selinux-pod
spec:
securityContext:
seLinuxOptions:
user: "system_u"
role: "system_r"
type: "spc_t"
level: "s0:c123,c456"
containers:
- name: secure-container
image: alpine
command: ["sleep", "3600"]apiVersion: v1
kind: Pod
metadata:
name: apparmor-pod
annotations:
container.apparmor.security.beta.kubernetes.io/secure-container: "localhost/docker-default"
spec:
containers:
- name: secure-container
image: alpine
command: ["sleep", "3600"]