Security

Updated Dec 29, 2023 ·

Some of the scenario questions here are based on Kodekloud's CKA course labs.

NOTE

CKAD and CKA can have similar scenario questions. It is recommended to go through the CKAD practice tests.

Shortcuts

First run the two commands below for shortcuts.

export do="--dry-run=client -o yaml" 
export now="--force --grace-period=0"

Questions

Kubectl suddenly stops responding to your commands. Check it out! Someone recently modified the /etc/kubernetes/manifests/etcd.yaml file

You are asked to investigate and fix the issue. Once you fix the issue wait for sometime for kubectl to respond. Check the logs of the ETCD container.

Answer

Check the certs.

controlplane ~ ➜  grep cert /etc/kubernetes/manifests/etcd.yaml
    - --cert-file=/etc/kubernetes/pki/etcd/server-certificate.crt
    - --client-cert-auth=true
    - --peer-cert-file=/etc/kubernetes/pki/etcd/peer.crt
    - --peer-client-cert-auth=true
    name: etcd-certs
    name: etcd-certs

controlplane ~ ➜  ls -la /etc/kubernetes/pki/etcd/
total 40
drwxr-xr-x 2 root root 4096 Dec 30 08:41 .
drwxr-xr-x 3 root root 4096 Dec 30 08:41 ..
-rw-r--r-- 1 root root 1086 Dec 30 08:41 ca.crt
-rw------- 1 root root 1679 Dec 30 08:41 ca.key
-rw-r--r-- 1 root root 1159 Dec 30 08:41 healthcheck-client.crt
-rw------- 1 root root 1675 Dec 30 08:41 healthcheck-client.key
-rw-r--r-- 1 root root 1208 Dec 30 08:41 peer.crt
-rw------- 1 root root 1679 Dec 30 08:41 peer.key
-rw-r--r-- 1 root root 1208 Dec 30 08:41 server.crt
-rw------- 1 root root 1679 Dec 30 08:41 server.key 

We can see above that the server cert defined is incorrect. Fix the YAML file.

--cert-file=/etc/kubernetes/pki/etcd/server.crt

The kube-api server stopped again! Check it out. Inspect the kube-api server logs and identify the root cause and fix the issue. Hint: Find the kube-apiserver container.

Answer

We can use crictl.

controlplane ~ ➜  crictl ps -a | grep apiserver
7ca09e4553971       6f707f569b572       2 minutes ago       Exited              kube-apiserver            5                   ec0124d62fe6d       kube-apiserver-controlplane

Then check logs.

controlplane ~ ➜  crictl logs 7ca09e4553971 | tail -1 

W1230 14:21:08.206143       1 logging.go:59] [core] [Channel #3 SubChannel #6] grpc: addrConn.createTransport failed to connect to {
"Addr": "127.0.0.1:2379",
"ServerName": "127.0.0.1",
"Attributes": null,
"BalancerAttributes": null,
"Type": 0,
"Metadata": null
}. Err: connection error: desc = "transport: authentication handshake failed: tls: failed to verify certificate: x509: certificate signed by unknown authority"
E1230 14:21:10.930501       1 run.go:74] "command failed" err="context deadline exceeded"

This could be an issue on the ETCD CA cert used. Check the certs.

controlplane ~ ✖ ls -la /etc/kubernetes/pki/
total 72
drwxr-xr-x 3 root root 4096 Dec 30 08:41 .
drwxr-xr-x 1 root root 4096 Dec 30 08:41 ..
-rw-r--r-- 1 root root 1289 Dec 30 08:41 apiserver.crt
-rw-r--r-- 1 root root 1155 Dec 30 08:41 apiserver-etcd-client.crt
-rw------- 1 root root 1675 Dec 30 08:41 apiserver-etcd-client.key
-rw------- 1 root root 1679 Dec 30 08:41 apiserver.key
-rw-r--r-- 1 root root 1164 Dec 30 08:41 apiserver-kubelet-client.crt
-rw------- 1 root root 1679 Dec 30 08:41 apiserver-kubelet-client.key
-rw-r--r-- 1 root root 1099 Dec 30 08:41 ca.crt
-rw------- 1 root root 1675 Dec 30 08:41 ca.key
drwxr-xr-x 2 root root 4096 Dec 30 08:41 etcd
-rw-r--r-- 1 root root 1115 Dec 30 08:41 front-proxy-ca.crt
-rw------- 1 root root 1679 Dec 30 08:41 front-proxy-ca.key
-rw-r--r-- 1 root root 1119 Dec 30 08:41 front-proxy-client.crt
-rw------- 1 root root 1679 Dec 30 08:41 front-proxy-client.key
-rw------- 1 root root 1675 Dec 30 08:41 sa.key
-rw------- 1 root root  451 Dec 30 08:41 sa.pub  

controlplane ~ ➜  ls -la /etc/kubernetes/pki/etcd/
total 40
drwxr-xr-x 2 root root 4096 Dec 30 08:41 .
drwxr-xr-x 3 root root 4096 Dec 30 08:41 ..
-rw-r--r-- 1 root root 1086 Dec 30 08:41 ca.crt
-rw------- 1 root root 1679 Dec 30 08:41 ca.key
-rw-r--r-- 1 root root 1159 Dec 30 08:41 healthcheck-client.crt
-rw------- 1 root root 1675 Dec 30 08:41 healthcheck-client.key
-rw-r--r-- 1 root root 1208 Dec 30 08:41 peer.crt
-rw------- 1 root root 1679 Dec 30 08:41 peer.key
-rw-r--r-- 1 root root 1208 Dec 30 08:41 server.crt
-rw------- 1 root root 1679 Dec 30 08:41 server.key

controlplane ~ ➜  ls -la /etc/kubernetes/manifests/
total 28
drwxr-xr-x 1 root root 4096 Dec 30 09:17 .
drwxr-xr-x 1 root root 4096 Dec 30 08:41 ..
-rw------- 1 root root 2399 Dec 30 09:16 etcd.yaml
-rw------- 1 root root 3872 Dec 30 09:17 kube-apiserver.yaml
-rw------- 1 root root 3393 Dec 30 08:41 kube-controller-manager.yaml
-rw------- 1 root root 1463 Dec 30 08:41 kube-scheduler.yaml  

controlplane ~ ➜  grep etcd /etc/kubernetes/manifests/kube-apiserver.yaml 
    - --etcd-cafile=/etc/kubernetes/pki/ca.crt
    - --etcd-certfile=/etc/kubernetes/pki/apiserver-etcd-client.crt
    - --etcd-keyfile=/etc/kubernetes/pki/apiserver-etcd-client.key
    - --etcd-servers=https://127.0.0.1:2379

Fix the --etcd-cafile in the YAML file.

--etcd-cafile=/etc/kubernetes/pki/etcd/ca.crt

A new member akshay joined our team. He requires access to our cluster. The Certificate Signing Request is at the /root location.

Create a CertificateSigningRequest object with the name akshay with the contents of the akshay.csr file
As of kubernetes 1.19, the API to use for CSR is certificates.k8s.io/v1.
Please note that an additional field called signerName should also be added when creating CSR.
For client authentication to the API server we will use the built-in signer kubernetes.io/kube-apiserver-client.
Approve the CSR Request

Answer

controlplane ~ ➜  ls -l
total 8
-rw-r--r-- 1 root root  887 Dec 30 09:36 akshay.csr
-rw------- 1 root root 1679 Dec 30 09:36 akshay.key 

Generate the base64 encoded format:

controlplane ~ ➜  cat akshay.csr | base64 -w 0

LS0tLS1CRUdJTiBDRVJUSUZJQ0FURSBSRVFVRVNULS0tLS0KTUlJQ1ZqQ0NBVDRDQVFBd0VURVBNQTBHQTFVRUF3d0dZV3R6YUdGNU1JSUJJakFOQmdrcW

Create the YAML file. Follow: https://kubernetes.io/docs/tasks/tls/managing-tls-in-a-cluster/#create-a-certificatesigningrequest-object-to-send-to-the-kubernetes-api

## akshay-csr.yaml 
apiVersion: certificates.k8s.io/v1
kind: CertificateSigningRequest
metadata:
  name: akshay
spec:
  request: LS0tLS1CRUdJTiBDRVJUSUZJQ0FURSBSRVFVRVNULS0tLS0KTUlJQ1ZqQ0NBVDRDQVFBd0VURVBNQTBHQTFVRUF3d0dZV3R6YUdGNU1JSUJJakFOQmdrcW
  signerName: kubernetes.io/kube-apiserver-client
  usages:
  - client auth 

controlplane ~ ➜  k apply -f akshay-csr.yaml 
certificatesigningrequest.certificates.k8s.io/akshay created

controlplane ~ ➜  k get csr
NAME        AGE   SIGNERNAME                                    REQUESTOR                  REQUESTEDDURATION   CONDITION
akshay      8s    kubernetes.io/kube-apiserver-client           kubernetes-admin           <none>              Pending
csr-fnjbq   20m   kubernetes.io/kube-apiserver-client-kubelet   system:node:controlplane   <none>              Approved,Issued 
    
controlplane ~ ➜  kubectl certificate approve akshay
certificatesigningrequest.certificates.k8s.io/akshay approved

controlplane ~ ➜  k get csr
NAME        AGE     SIGNERNAME                                    REQUESTOR                  REQUESTEDDURATION   CONDITION
akshay      3m10s   kubernetes.io/kube-apiserver-client           kubernetes-admin           <none>              Approved,Issued
csr-fnjbq   23m     kubernetes.io/kube-apiserver-client-kubelet   system:node:controlplane   <none>              Approved,Issued    

There is a new CSR. What groups is this CSR requesting access to?

We need to reject it.
After rejecting, delete the CSR.

controlplane ~ ➜  k get csr
NAME          AGE     SIGNERNAME                                    REQUESTOR                  REQUESTEDDURATION   CONDITION
agent-smith   7s      kubernetes.io/kube-apiserver-client           agent-x                    <none>              Pending
akshay        4m13s   kubernetes.io/kube-apiserver-client           kubernetes-admin           <none>              Approved,Issued
csr-fnjbq     24m     kubernetes.io/kube-apiserver-client-kubelet   system:node:controlplane   <none>              Approved,Issued 

Answer

controlplane ~ ➜  k get csr agent-smith -o yaml
apiVersion: certificates.k8s.io/v1
kind: CertificateSigningRequest
metadata:
  creationTimestamp: "2023-12-30T14:54:23Z"
  name: agent-smith
resourceVersion: "2368"
uid: 91311095-f323-42a0-a704-db17451ef8ff
spec:
  groups:
  - system:masters
  - system:authenticated
  request: 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
  signerName: kubernetes.io/kube-apiserver-client
  usages:
  - digital signature
  - key encipherment
  - server auth
username: agent-x
status: {} 

controlplane ~ ➜  k get csr
NAME          AGE     SIGNERNAME                                    REQUESTOR                  REQUESTEDDURATION   CONDITION
agent-smith   2m53s   kubernetes.io/kube-apiserver-client           agent-x                    <none>              Pending
akshay        6m59s   kubernetes.io/kube-apiserver-client           kubernetes-admin           <none>              Approved,Issued
csr-fnjbq     27m     kubernetes.io/kube-apiserver-client-kubelet   system:node:controlplane   <none>              Approved,Issued

controlplane ~ ➜  kubectl certificate deny agent-smith
certificatesigningrequest.certificates.k8s.io/agent-smith denied

controlplane ~ ➜  k get csr
NAME          AGE     SIGNERNAME                                    REQUESTOR                  REQUESTEDDURATION   CONDITION
agent-smith   3m9s    kubernetes.io/kube-apiserver-client           agent-x                    <none>              Denied
akshay        7m15s   kubernetes.io/kube-apiserver-client           kubernetes-admin           <none>              Approved,Issued
csr-fnjbq     27m     kubernetes.io/kube-apiserver-client-kubelet   system:node:controlplane   <none>              Approved,Issued

To delete the CSR, generate the YAML and use the kubectl delete.

controlplane ~ ➜  k get csr agent-smith -o yaml > agent-smith.yml

controlplane ~ ➜  k delete -f agent-smith.yml 
certificatesigningrequest.certificates.k8s.io "agent-smith" deleted

controlplane ~ ➜  k get csr
NAME        AGE     SIGNERNAME                                    REQUESTOR                  REQUESTEDDURATION   CONDITION
akshay      9m59s   kubernetes.io/kube-apiserver-client           kubernetes-admin           <none>              Approved,Issued
csr-fnjbq   30m     kubernetes.io/kube-apiserver-client-kubelet   system:node:controlplane   <none>              Approved,Issued  

Where is the default kubeconfig file located in the current environment?

Answer

The answer is /root/.kube/config

controlplane ~ ➜  ls -la
total 60
drwx------ 1 root root 4096 Dec 30 10:02 .
drwxr-xr-x 1 root root 4096 Dec 30 09:57 ..
-rw-r--r-- 1 root root 1272 Dec 30 09:57 .bash_profile
-rw-r--r-- 1 root root 3265 Nov  2 11:39 .bashrc
drwxr-xr-x 1 root root 4096 Dec 30 10:02 .cache
drwxr-xr-x 2 root root 4096 Dec 30 10:02 CKA
drwxr-xr-x 1 root root 4096 Nov  2 11:36 .config
drwxr-xr-x 3 root root 4096 Dec 30 10:02 .kube
-rw-rw-rw- 1 root root 1456 Dec 30 10:02 my-kube-config
-rw-r--r-- 1 root root  161 Dec  5  2019 .profile
-rw-rw-rw- 1 root root    0 Dec 13 05:39 sample.yaml
drwx------ 2 root root 4096 Dec 30 10:02 .ssh
drwxr-xr-x 4 root root 4096 Nov  2 11:37 .vim
-rw-r--r-- 1 root root  132 Nov  2 11:37 .vimrc
-rw-r--r-- 1 root root  165 Nov  2 11:38 .wget-hsts

controlplane ~ ➜  ls -la .kube/
total 24
drwxr-xr-x 3 root root 4096 Dec 30 10:02 .
drwx------ 1 root root 4096 Dec 30 10:02 ..
drwxr-x--- 4 root root 4096 Dec 30 10:02 cache
-rw------- 1 root root 5640 Dec 30 09:57 config 

In the default kubeconfig file, what is the user configured in the current context?

Answer

controlplane ~/.kube ➜  grep -i context config
contexts:
- context:
current-context: kubernetes-admin@kubernetes

controlplane ~/.kube ➜  grep -i current-context -A 5 config
current-context: kubernetes-admin@kubernetes
kind: Config
preferences: {}
users:
- name: kubernetes-admin 

A new kubeconfig file named my-kube-config is created. It is placed in the /root directory. How many clusters are defined in that kubeconfig file?

Answer

controlplane ~ ➜  ls -l
total 8
drwxr-xr-x 2 root root 4096 Dec 30 10:02 CKA
-rw-rw-rw- 1 root root 1456 Dec 30 10:08 my-kube-config
-rw-rw-rw- 1 root root    0 Dec 13 05:39 sample.yaml

controlplane ~ ➜  grep cluster my-kube-config 
clusters:
cluster:
cluster:
cluster:
- name: test-cluster-1
cluster:
    cluster: development
    cluster: kubernetes-on-aws
    cluster: production
    cluster: test-cluster-1 

In the new my-kube-config, what user is configured in the research context?

Answer

controlplane ~ ➜  grep -A 5 research my-kube-config 
- name: research
context:
    cluster: test-cluster-1
    user: dev-user 

In the new my-kube-config, what is the name of the client-certificate file configured for the aws-user?

Answer

controlplane ~ ➜  grep -A 10 aws-user  my-kube-config

--
- name: aws-user
user:
    client-certificate: /etc/kubernetes/pki/users/aws-user/aws-user.crt
    client-key: /etc/kubernetes/pki/users/aws-user/aws-user.key

I would like to use the dev-user to access test-cluster-1. Set the current context to the right one so I can do that.

Once the right context is identified, use the kubectl config use-context command.

Answer

controlplane ~ ✖ k config --kubeconfig my-kube-config get-contexts
CURRENT   NAME                         CLUSTER             AUTHINFO    NAMESPACE
        aws-user@kubernetes-on-aws   kubernetes-on-aws   aws-user    
        research                     test-cluster-1      dev-user    
*         test-user@development        development         test-user   
        test-user@production         production          test-user  

controlplane ~ ➜  k config --kubeconfig my-kube-config use-context research
Switched to context "research".

controlplane ~ ➜  k config --kubeconfig my-kube-config get-contexts
CURRENT   NAME                         CLUSTER             AUTHINFO    NAMESPACE
        aws-user@kubernetes-on-aws   kubernetes-on-aws   aws-user    
*         research                     test-cluster-1      dev-user    
        test-user@development        development         test-user   
        test-user@production         production          test-user            

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