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Version - 2025.01
Last update : 2025/01/17 16:05
DOE308 - Introduction to Securing K8s
Contents
- DOE308 - Introduction to Securing K8s
- Contents
- LAB #1 - Role Based Access Control and TLS Certificates
- 1.1 - Overview
- 1.2 - The /etc/kubernetes/manifests/kube-apiserver.yaml file
- 1.3 - Creating a serviceAccount
- 1.4 - User creation
- 1.5 - TLS certificates
- LAB #2 - Implementing security at Pod level
- 2.1 - Overview
- 2.2 - Kubernetes Security Context
- ReadOnlyRootFilesystem
- drop
- 2.3 - Kubernetes Network Policies
- 2.4 - Kubernetes Resource Allocation Management
LAB #1 - Role Based Access Control and TLS Certificates
001.1 - Overview
A Kubernetes object is either linked to a Namespace or not linked to a Namespace.
Kubernetes uses the rbac.authorization.k8s.io API to manage authorizations. The actors involved in this API are:
- Namespaces,
- can be considered as virtual clusters,
- allow isolation and logical segmentation,
- allow users, roles and resources to be grouped together,
- are used with applications, customers, projects or teams.
- Subjects,
- Regular Users - enable management of authorized access from outside the cluster, whether by a physical user or in some other form. User management is the responsibility of the cluster administrator,
- ServiceAccounts - set permissions on software entities. Kubernetes creates a certain number of serviceAccounts automatically, but the Administrator can create others. Each pod has a serviceAccount that manages the privileges granted to the pod's process and containers,
- User Groups - Kubernetes groups users using common properties such as the prefix of a serviceAccount or the organization field in a certificate. It is then possible to grant RBAC-type privileges to the groups thus created.
- Resources,
- These are entities to which Subjects will have access,
- A resource is an entity such as a pod, a deployment or sub-resources such as pod logs,
- The Pod Security Policy (PSP) is also considered a resource.
- Roles and ClusterRoles,
- Roles - allow you to define rules representing a set of permissions, such as GET WATCH LIST CREATE UPDATE PATCH and DELETE, which can be used with resources in a Namespace,
- Permissions are added, not removed. So there are no deny rules.
- ClusterRoles - is not linked to a Namespace. A ClusterRole is used to :
- Define permissions for resources to be used in a Namespace
- Set permissions for resources to be used in all Namespaces
- Set permissions for cluster resources.
An example of a Role for granting permissions in the default Namespace is :
apiVersion: rbac.authorization.k8s.io/v1 kind: Role metadata: namespace: default name: pod-reader rules: - apiGroups: [""] resources: ["pods"] verbs: ["get", "watch", "list"]
Important : apiGroups: [“”] - “” indicates the core or legacy api group. This group is never specified in an apiVersion field, which is why we write apiVersion: v1 and not apiVersion api/v1.
An example of a ClusterRole for granting read permissions to secrets in a specific Namespace or in all Namespaces is :
apiVersion: rbac.authorization.k8s.io/v1 kind: ClusterRole metadata: name: secret-reader rules: - apiGroups: [""] resources: ["secrets"] verbs: ["get", "watch", "list"]
- RoleBindings and ClusterRoleBindings,
- Allow you to grant permissions defined in Roles or ClusterRoles to Subjects,
- RoleBindings are NameSpace-specific,
- ClusterRoleBindings apply at cluster level.
1.2 - The /etc/kubernetes/manifests/kube-apiserver.yaml File
The use of RBAC is defined by the value of the –authorization-mode directive in the /etc/kubernetes/manifests/kube-apiserver.yaml file:
root@kubemaster:~# cat /etc/kubernetes/manifests/kube-apiserver.yaml
apiVersion: v1
kind: Pod
metadata:
annotations:
kubeadm.kubernetes.io/kube-apiserver.advertise-address.endpoint: 192.168.56.2:6443
creationTimestamp: null
labels:
component: kube-apiserver
tier: control-plane
name: kube-apiserver
namespace: kube-system
spec:
containers:
- command:
- kube-apiserver
- --advertise-address=192.168.56.2
- --allow-privileged=true
- --authorization-mode=Node,RBAC
- --client-ca-file=/etc/kubernetes/pki/ca.crt
- --enable-admission-plugins=NodeRestriction
- --enable-bootstrap-token-auth=true
- --etcd-cafile=/etc/kubernetes/pki/etcd/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
- --kubelet-client-certificate=/etc/kubernetes/pki/apiserver-kubelet-client.crt
- --kubelet-client-key=/etc/kubernetes/pki/apiserver-kubelet-client.key
- --kubelet-preferred-address-types=InternalIP,ExternalIP,Hostname
- --proxy-client-cert-file=/etc/kubernetes/pki/front-proxy-client.crt
- --proxy-client-key-file=/etc/kubernetes/pki/front-proxy-client.key
- --requestheader-allowed-names=front-proxy-client
- --requestheader-client-ca-file=/etc/kubernetes/pki/front-proxy-ca.crt
- --requestheader-extra-headers-prefix=X-Remote-Extra-
- --requestheader-group-headers=X-Remote-Group
- --requestheader-username-headers=X-Remote-User
- --secure-port=6443
- --service-account-issuer=https://kubernetes.default.svc.cluster.local
- --service-account-key-file=/etc/kubernetes/pki/sa.pub
- --service-account-signing-key-file=/etc/kubernetes/pki/sa.key
- --service-cluster-ip-range=10.96.0.0/12
- --tls-cert-file=/etc/kubernetes/pki/apiserver.crt
- --tls-private-key-file=/etc/kubernetes/pki/apiserver.key
image: k8s.gcr.io/kube-apiserver:v1.24.2
imagePullPolicy: IfNotPresent
livenessProbe:
failureThreshold: 8
httpGet:
host: 192.168.56.2
path: /livez
port: 6443
scheme: HTTPS
initialDelaySeconds: 10
periodSeconds: 10
timeoutSeconds: 15
name: kube-apiserver
readinessProbe:
failureThreshold: 3
httpGet:
host: 192.168.56.2
path: /readyz
port: 6443
scheme: HTTPS
periodSeconds: 1
timeoutSeconds: 15
resources:
requests:
cpu: 250m
startupProbe:
failureThreshold: 24
httpGet:
host: 192.168.56.2
path: /livez
port: 6443
scheme: HTTPS
initialDelaySeconds: 10
periodSeconds: 10
timeoutSeconds: 15
volumeMounts:
- mountPath: /etc/ssl/certs
name: ca-certs
readOnly: true
- mountPath: /etc/ca-certificates
name: etc-ca-certificates
readOnly: true
- mountPath: /etc/kubernetes/pki
name: k8s-certs
readOnly: true
- mountPath: /usr/local/share/ca-certificates
name: usr-local-share-ca-certificates
readOnly: true
- mountPath: /usr/share/ca-certificates
name: usr-share-ca-certificates
readOnly: true
hostNetwork: true
priorityClassName: system-node-critical
securityContext:
seccompProfile:
type: RuntimeDefault
volumes:
- hostPath:
path: /etc/ssl/certs
type: DirectoryOrCreate
name: ca-certs
- hostPath:
path: /etc/ca-certificates
type: DirectoryOrCreate
name: etc-ca-certificates
- hostPath:
path: /etc/kubernetes/pki
type: DirectoryOrCreate
name: k8s-certs
- hostPath:
path: /usr/local/share/ca-certificates
type: DirectoryOrCreate
name: usr-local-share-ca-certificates
- hostPath:
path: /usr/share/ca-certificates
type: DirectoryOrCreate
name: usr-share-ca-certificates
status: {}
1.3 - Creating a serviceAccount
It is preferable to create one serviceAccount per service. This allows you to fine-tune the security settings for the service. If a serviceAccount is not specified when pods are created, these pods will be assigned the Namespace default serviceAccount.
Let's say you want your application to interact with the Kubernetes API to obtain information about pods in a Namespace. The default serviceAccount in the Namespace default cannot perform this task:
root@kubemaster:~# kubectl auth can-i list pods -n default --as=system:serviceaccount:default:default no
Important: the format of the –as option value is system:serviceaccount:namespace:serviceaccount_name.
Now create the flask.yaml file:
To do: Copy the content from here and paste it into your file.
root@kubemaster:~# vi flask.yaml
root@kubemaster:~# cat flask.yaml
apiVersion: v1
kind: Namespace
metadata:
name: flask
---
apiVersion: v1
kind: ServiceAccount
metadata:
name: flask-backend
namespace: flask
---
kind: Role
apiVersion: rbac.authorization.k8s.io/v1
metadata:
name: flask-backend-role
namespace: flask
rules:
- apiGroups: [""]
resources: ["pods"]
verbs: ["get", "list", "watch"]
---
kind: RoleBinding
apiVersion: rbac.authorization.k8s.io/v1
metadata:
name: flask-backend-role-binding
namespace: flask
subjects:
- kind: ServiceAccount
name: flask-backend
namespace: flask
roleRef:
kind: Role
name: flask-backend-role
apiGroup: rbac.authorization.k8s.io
This file creates :
- a Namespace called flask,
- a serviceAccount called flask-backend for the Namespace flask,
- a Role called flask-backend-role that grants get, watch and list permissions on pods in the flask Namespace,
- a RoleBinding called flask-backend-role-binding that grants the permissions defined in the flask-backend-role Role to the serviceAccount called flask-backend.
Apply the yaml file:
root@kubemaster:~# kubectl create -f flask.yaml namespace/flask created serviceaccount/flask-backend created role.rbac.authorization.k8s.io/flask-backend-role created rolebinding.rbac.authorization.k8s.io/flask-backend-role-binding created
Now create the deployment.yaml file that creates pods that will use the serviceAccount called flask-backend:
To do: Copy the content from here and paste it into your file.
root@kubemaster:~# vi deployment.yaml
root@kubemaster:~# cat deployment.yaml
---
apiVersion: apps/v1
kind: Deployment
metadata:
name: myapp-deployment
namespace: flask
labels:
app: myapp
type: front-end
spec:
template:
metadata:
name: myapp-pod
labels:
app: myapp
type: front-end
spec:
serviceAccount: flask-backend
containers:
- name: nginx-container
image: nginx
replicas: 3
selector:
matchLabels:
type: front-end
Run kubectl :
root@kubemaster:~# kubectl create -f deployment.yaml deployment.apps/myapp-deployment created
Check the presence of the deployment:
root@kubemaster:~# kubectl get deployment -n flask NAME READY UP-TO-DATE AVAILABLE AGE myapp-deployment 3/3 3 3 32s
Now check that the serviceAccount flask-backend can list pods in the Namespace flask :
root@kubemaster:~# kubectl auth can-i list pods -n flask --as=system:serviceaccount:flask:flask-backend yes
Note, however, that the flask-backend serviceAccount does not have the create permission in the flask Namespace:
root@kubemaster:~# kubectl auth can-i create pods -n flask --as=system:serviceaccount:flask:flask-backend no
and the flask-backend serviceAccount does not have the list permission in the default Namespace:
root@kubemaster:~# kubectl auth can-i list pods -n default --as=system:serviceaccount:flask:flask-backend no
1.4 - Creating a user
Users are part of the configuration context that defines the cluster name and the namespace name:
root@kubemaster:~# kubectl config get-contexts CURRENT NAME CLUSTER AUTHINFO NAMESPACE * kubernetes-admin@kubernetes kubernetes kubernetes-admin
Important: A context is an element that groups access parameters under a name. There are three access parameters: cluster, namespace and user. The kubectl command uses the parameters of the current context to communicate with the cluster.
Looking at the current context, we see that the user kubernetes-admin@kubernetes has two attributes named :
- client-certificate-data: REDACTED
- client-key-data: REDACTED
root@kubemaster:~# kubectl config view
apiVersion: v1
clusters:
- cluster:
certificate-authority-data: DATA+OMITTED
server: https://192.168.56.2:6443
name: kubernetes
contexts:
- context:
cluster: kubernetes
user: kubernetes-admin
name: kubernetes-admin@kubernetes
current-context: kubernetes-admin@kubernetes
kind: Config
preferences: {}
users:
- name: kubernetes-admin
user:
client-certificate-data: REDACTED
client-key-data: REDACTED
Important : The word REDACTED indicates that the values are hidden for security reasons.
To create a new user, first create a private key for the user:
root@kubemaster:~# openssl genrsa -out trainee.key 2048 Generating RSA private key, 2048 bit long modulus ....................................+++ ..............+++ e is 65537 (0x10001)
Now create a CSR:
root@kubemaster:~# openssl req -new -key trainee.key -out trainee.csr -subj “/CN=trainee/O=examplegroup”
Important: Note that Kubernetes will use the organization key value for user grouping.
The CSR must be signed by the Kubernetes root CA:
root@kubemaster:~# ls -l /etc/kubernetes/pki/ca.* -rw-r--r-- 1 root root 1099 Jul 12 13:23 /etc/kubernetes/pki/ca.crt -rw------- 1 root root 1679 Jul 12 13:23 /etc/kubernetes/pki/ca.key
Sign the CSR :
root@kubemaster:~# openssl x509 -req -in trainee.csr -CA /etc/kubernetes/pki/ca.crt -CAkey /etc/kubernetes/pki/ca.key -CAcreateserial -out trainee.crt Signature ok subject=/CN=trainee/O=examplegroup Getting CA Private Key
View the trainee certificate :
root@kubemaster:~# openssl x509 -in trainee.crt -text
Certificate:
Data:
Version: 1 (0x0)
Serial Number:
b6:f7:59:8f:75:19:bc:10
Signature Algorithm: sha256WithRSAEncryption
Issuer: CN = kubernetes
Validity
Not Before: Jul 14 07:49:14 2022 GMT
Not After : Aug 13 07:49:14 2022 GMT
Subject: CN = trainee, O = examplegroup
Subject Public Key Info:
Public Key Algorithm: rsaEncryption
Public-Key: (2048 bit)
Modulus:
00:9b:2d:e8:7d:ba:e9:9f:b3:da:8f:14:13:21:83:
64:c6:6e:7b:2c:ee:4f:e6:71:65:a7:e4:ca:6a:23:
ee:cf:e1:43:18:e0:b0:1f:ef:ff:53:21:de:d2:e8:
38:d1:39:ab:b0:8d:78:f4:af:7c:80:b0:1a:c3:a2:
cb:64:b4:73:e6:a5:30:33:69:f1:6d:9a:5b:66:2e:
58:f6:c2:51:7c:42:95:16:ac:60:0e:1d:4d:09:aa:
06:29:51:79:f1:45:70:48:b9:1c:e2:05:fc:5c:33:
82:d7:82:5f:a2:31:13:b5:23:4c:10:bf:a5:8a:4f:
37:2a:d6:cc:ac:c7:c0:ad:97:71:95:9e:26:4f:60:
b5:41:8a:7b:c5:79:38:02:28:b0:88:84:23:0b:18:
d2:c2:f9:9f:ff:ec:ec:fb:0a:41:d7:7d:f3:90:2f:
29:08:86:1e:e7:cb:ab:cf:56:5e:a9:ba:06:d8:83:
c2:3c:1d:38:cc:fa:fd:69:17:4e:c3:7e:79:dd:34:
11:9a:ff:5d:32:e4:68:a8:0f:cc:4c:bf:27:bc:2e:
19:b7:9d:ad:68:45:d9:87:06:74:9f:e4:ad:bf:df:
06:c8:28:c7:a4:78:f2:31:b2:6c:c7:9e:90:b8:bf:
48:d4:ae:fd:65:e9:38:fd:8f:30:41:e9:32:f5:de:
69:69
Exponent: 65537 (0x10001)
Signature Algorithm: sha256WithRSAEncryption
6d:c8:0d:cd:7c:34:5c:08:67:98:b6:ae:80:26:e8:73:f1:14:
3b:02:09:dd:b4:6d:f1:7f:bb:12:8a:16:86:d6:d6:be:ad:92:
99:a8:23:a1:d7:de:d4:e9:03:ec:6f:b9:19:46:2d:d8:f4:30:
71:8c:f0:6e:43:ad:d8:10:46:15:ab:9f:46:c1:56:4c:6c:81:
ab:ba:dd:5b:78:6a:57:82:d3:1a:d7:1a:5f:63:ca:4e:0f:fb:
ce:fe:f1:a5:78:64:a5:03:41:ad:c5:b7:28:45:62:31:ce:02:
09:1b:73:1d:e0:96:a4:1b:c4:09:18:a6:b1:5e:8c:88:03:75:
92:64:47:d3:0c:ce:87:91:9c:25:f7:72:a7:44:9d:36:41:87:
48:61:71:31:9a:24:ae:36:4f:40:c8:f3:08:32:f5:b1:9d:f5:
8a:0a:71:80:e6:70:d9:af:e1:96:55:81:9f:a1:95:39:53:b5:
1b:f3:37:3e:50:d5:a1:6b:d1:4b:d1:c6:75:fb:63:f0:63:06:
ce:99:fb:c3:15:c1:51:3b:ed:d9:c8:68:43:66:3c:ef:92:ba:
ae:a5:0d:02:48:8d:42:1a:70:22:13:75:47:ad:69:d5:48:11:
6b:b1:24:80:7e:d6:0d:f7:92:0c:bb:28:91:6e:d4:4c:a1:14:
c9:2d:47:2c
-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----
Create a second user in the same Organization:
root@kubemaster:~# openssl genrsa -out stagiaire.key 2048 Generating RSA private key, 2048 bit long modulus ................................................................................................................................+++ .................+++ e is 65537 (0x10001) root@kubemaster:~# openssl req -new -key stagiaire.key -out stagiaire.csr -subj “/CN=stagiaire/O=examplegroup” root@kubemaster:~# openssl x509 -req -in stagiaire.csr -CA /etc/kubernetes/pki/ca.crt -CAkey /etc/kubernetes/pki/ca.key -CAcreateserial -out stagiaire.crt Signature ok subject=/CN=stagiaire/O=examplegroup Getting CA Private Key
Now create the trainee context:
root@kubemaster:~# kubectl config set-credentials trainee --client-certificate=trainee.crt --client-key=trainee.key User “trainee” set. root@kubemaster:~# kubectl config set-context trainee@kubernetes --cluster=kubernetes --user=trainee Context “trainee@kubernetes” created.
Check that the context is present:
root@kubemaster:~# kubectl config get-contexts
CURRENT NAME CLUSTER AUTHINFO NAMESPACE
* kubernetes-admin@kubernetes kubernetes kubernetes-admin
trainee@kubernetes kubernetes trainee
Use the trainee context :
root@kubemaster:~# kubectl config use-context trainee@kubernetes
Switched to context "trainee@kubernetes".
root@kubemaster:~# kubectl config get-contexts
CURRENT NAME CLUSTER AUTHINFO NAMESPACE
kubernetes-admin@kubernetes kubernetes kubernetes-admin
* trainee@kubernetes kubernetes trainee
root@kubemaster:~# kubectl get pods
Error from server (Forbidden): pods is forbidden: User "trainee" cannot list resource "pods" in API group "" in the namespace "default"
Important: Note that trainee cannot list pods because RBAC permissions have not been set.
Return to the administrator context:
root@kubemaster:~# kubectl config use-context kubernetes-admin@kubernetes
Switched to context "kubernetes-admin@kubernetes".
root@kubemaster:~# kubectl config get-contexts
CURRENT NAME CLUSTER AUTHINFO NAMESPACE
* kubernetes-admin@kubernetes kubernetes kubernetes-admin
trainee@kubernetes kubernetes trainee
Now create a clusterrolebinding for the examplegroup :
root@kubemaster:~# kubectl create clusterrolebinding examplegroup-admin-binding --clusterrole=cluster-admin --group=examplegroup clusterrolebinding.rbac.authorization.k8s.io/examplegroup-admin-binding created
Use the trainee context again:
root@kubemaster:~# kubectl config use-context trainee@kubernetes
Switched to context "trainee@kubernetes".
root@kubemaster:~# kubectl config get-contexts
CURRENT NAME CLUSTER AUTHINFO NAMESPACE
kubernetes-admin@kubernetes kubernetes kubernetes-admin
* trainee@kubernetes kubernetes trainee
root@kubemaster:~# kubectl get pods -n kube-system
NAME READY STATUS RESTARTS AGE
calico-kube-controllers-6766647d54-v4hrm 1/1 Running 0 44h
calico-node-5mrjl 1/1 Running 0 41h
calico-node-688lw 1/1 Running 0 44h
calico-node-j25xd 1/1 Running 0 41h
coredns-6d4b75cb6d-dw4ph 1/1 Running 0 44h
coredns-6d4b75cb6d-ms2jm 1/1 Running 0 44h
etcd-kubemaster.ittraining.loc 1/1 Running 1 (44h ago) 44h
kube-apiserver-kubemaster.ittraining.loc 1/1 Running 1 (44h ago) 44h
kube-controller-manager-kubemaster.ittraining.loc 1/1 Running 10 (75m ago) 44h
kube-proxy-bwctz 1/1 Running 0 41h
kube-proxy-j89vg 1/1 Running 0 41h
kube-proxy-jx76x 1/1 Running 0 44h
kube-scheduler-kubemaster.ittraining.loc 1/1 Running 11 (75m ago) 44h
metrics-server-7cb867d5dc-g55k5 1/1 Running 0 28h
1.5 - TLS certificates
By default, communication between kubectl and the Kubernetes API is encrypted. Certificates are located in the /var/lib/kubelet/pki/ directory of each node:
root@kubemaster:~# ls -l /var/lib/kubelet/pki/ total 12 -rw------- 1 root root 2851 Jul. 12 13:23 kubelet-client-2022-07-12-13-23-12.pem lrwxrwxrwx 1 root root 59 Jul. 12 13:23 kubelet-client-current.pem -> /var/lib/kubelet/pki/kubelet-client-2022-07-12-13-23-12.pem -rw-r--r-- 1 root root 2367 Jul. 12 13:23 kubelet.crt -rw------- 1 root root 1675 Jul. 12 13:23 kubelet.key
Important: By default, kubelet certificates expire after one year.
LAB #2 - Pod Security Implementation
2.1 - Overview
An Admission Controller is a piece of code that intercepts requests to the Kubernetes API. The use of Admission Controllers is defined by the –admission-control directive in the /etc/kubernetes/manifests/kube-apiserver.yaml file, for example :
--admission-control=Initializers, NamespaceLifecycle, LimitRanger, ServiceAccount, PersistentVolumeLabel, DefaultStorageClass, DefaultTolerationSeconds, NodeRestriction, ResourceQuota
The most important Admission Controllers in terms of security are :
- DenyEscalatingExec,
- Prohibits the execution of commands with an escalated container in a privileged pod. The commands concerned are exec and attach. An escalated container in a privileged pod is not isolated and therefore allows access to the host.
- NodeRestriction,
- Limits the number of node and pod objects that kubectl can modify,
- PodSecurityPolicy,
- Acts when a pod is created or modified to decide whether it can be admitted to the cluster according to the Security Context and applicable policies,
- ValidatingAdmissionWebhooks,
- Allows you to call an external service that implements a security policy, such as Grafeas.
2.2 - Kubernetes Security Context
The Security Context is configured from the pod or container. Here are a few examples.
ReadOnlyRootFilesystem
Create the file readonly.yaml:
To do: Copy the content from here and paste it into your file.
root@kubemaster:~# vi readonly.yaml
root@kubemaster:~# cat readonly.yaml
apiVersion: v1
kind: Pod
metadata:
name: flask-ro
namespace: default
spec:
containers:
- image: mateobur/flask
name: flask-ro
securityContext:
readOnlyRootFilesystem: true
Run kubectl :
root@kubemaster:~# kubectl create -f readonly.yaml pod/flask-ro created
Check that the pod is in READY state:
root@kubemaster:~# kubectl get pods NAME READY STATUS RESTARTS AGE flask-ro 1/1 Running 0 13m postgres-deployment-5b8bd66778-j99zz 1/1 Running 7 4d1h redis-deployment-67d4c466c4-9wzfn 1/1 Running 7 4d1h result-app-deployment-b8f9dc967-nzbgd 1/1 Running 7 4d1h result-app-deployment-b8f9dc967-r84k6 1/1 Running 7 3d22h result-app-deployment-b8f9dc967-zbsk2 1/1 Running 7 3d22h voting-app-deployment-669dccccfb-jpn6h 1/1 Running 7 4d1h voting-app-deployment-669dccccfb-ktd7d 1/1 Running 7 3d22h voting-app-deployment-669dccccfb-x868p 1/1 Running 7 3d22h worker-app-deployment-559f7749b6-jh86r 1/1 Running 19 4d1h
Connect to the container:
root@kubemaster:~# kubectl exec -it flask-ro bash root@flask-ro:/#
Note that the system is read-only:
root@flask-ro:/# mount | grep “/ ” overlay on / type overlay (ro,relatime,lowerdir=/var/lib/containerd/io.containerd.snapshotter.v1.overlayfs/snapshots/72/fs:/var/lib/containerd/io.containerd.snapshotter.v1.overlayfs/snapshots/71/fs:/var/lib/containerd/io.containerd.snapshotter.v1. overlayfs/snapshots/70/fs:/var/lib/containerd/io.containerd.snapshotter.v1.overlayfs/snapshots/69/fs,upperdir=/var/lib/containerd/io.containerd.snapshotter.v1.overlayfs/snapshots/73/fs,workdir=/var/lib/containerd/io.containerd.snapshotter.v1.overlayfs/snapshots/73/work) root@flask-ro:/# touch test touch: cannot touch 'test': Read-only file system root@flask-ro:/# exit exit command terminated with exit code 1
drop
Create the file drop.yaml:
To do: Copy the content from here and paste it into your file.
root@kubemaster:~# vi drop.yaml
root@kubemaster:~# cat drop.yaml
apiVersion: v1
kind: Pod
metadata:
name: flask-cap
namespace: default
spec:
containers:
- image: mateobur/flask
name: flask-cap
securityContext:
capabilities:
drop:
- NET_RAW
- CHOWN
Run kubectl :
root@kubemaster:~# kubectl create -f drop.yaml pod/flask-cap created
Check that the pod is in a READY state:
root@kubemaster:~# kubectl get pods NAME READY STATUS RESTARTS AGE flask-cap 1/1 Running 0 4m4s flask-ro 1/1 Running 0 13m postgres-deployment-5b8bd66778-j99zz 1/1 Running 7 4d1h redis-deployment-67d4c466c4-9wzfn 1/1 Running 7 4d1h result-app-deployment-b8f9dc967-nzbgd 1/1 Running 7 4d1h result-app-deployment-b8f9dc967-r84k6 1/1 Running 7 3d22h result-app-deployment-b8f9dc967-zbsk2 1/1 Running 7 3d22h voting-app-deployment-669dccccfb-jpn6h 1/1 Running 7 4d1h voting-app-deployment-669dccccfb-ktd7d 1/1 Running 7 3d22h voting-app-deployment-669dccccfb-x868p 1/1 Running 7 3d22h worker-app-deployment-559f7749b6-jh86r 1/1 Running 19 4d1h
Connect to the container:
root@kubemaster:~# kubectl exec -it flask-cap -- bash root@flask-cap:/#
Note the restrictions:
root@flask-cap:/# ping 8.8.8.8 ping: Lacking privilege for raw socket. root@flask-cap:/# chown daemon /tmp chown: changing ownership of '/tmp': Operation not permitted root@flask-cap:/# exit exit command terminated with exit code 1
2.3 - Kubernetes Network Policies
Create the file guestbook-all-in-one.yaml :
To do: Copy the content from here and paste it into your file.
root@kubemaster:~# vi guestbook-all-in-one.yaml
root@kubemaster:~# cat guestbook-all-in-one.yaml
apiVersion: v1
kind: Service
metadata:
name: redis-master
labels:
app: redis
tier: backend
role: master
spec:
ports:
# the port that this service should serve on
- port: 6379
targetPort: 6379
selector:
app: redis
tier: backend
role: master
---
apiVersion: v1
kind: ReplicationController
metadata:
name: redis-master
# these labels can be applied automatically
# from the labels in the pod template if not set
labels:
app: redis
role: master
tier: backend
spec:
# this replicas value is default
# modify it according to your case
replicas: 1
# selector can be applied automatically
# from the labels in the pod template if not set
# selector:
# app: guestbook
# role: master
# tier: backend
template:
metadata:
labels:
app: redis
role: master
tier: backend
spec:
containers:
- name: master
image: gcr.io/google_containers/redis:e2e # or just image: redis
resources:
requests:
cpu: 100m
memory: 100Mi
ports:
- containerPort: 6379
---
apiVersion: v1
kind: Service
metadata:
name: redis-slave
labels:
app: redis
tier: backend
role: slave
spec:
ports:
# the port that this service should serve on
- port: 6379
selector:
app: redis
tier: backend
role: slave
---
apiVersion: v1
kind: ReplicationController
metadata:
name: redis-slave
# these labels can be applied automatically
# from the labels in the pod template if not set
labels:
app: redis
role: slave
tier: backend
spec:
# this replicas value is default
# modify it according to your case
replicas: 2
# selector can be applied automatically
# from the labels in the pod template if not set
# selector:
# app: guestbook
# role: slave
# tier: backend
template:
metadata:
labels:
app: redis
role: slave
tier: backend
spec:
containers:
- name: slave
image: gcr.io/google_samples/gb-redisslave:v1
resources:
requests:
cpu: 100m
memory: 100Mi
env:
- name: GET_HOSTS_FROM
value: dns
# If your cluster config does not include a dns service, then to
# instead access an environment variable to find the master
# service's host, comment out the 'value: dns' line above, and
# uncomment the line below.
# value: env
ports:
- containerPort: 6379
---
apiVersion: v1
kind: Service
metadata:
name: frontend
labels:
app: guestbook
tier: frontend
spec:
# if your cluster supports it, uncomment the following to automatically create
# an external load-balanced IP for the frontend service.
# type: LoadBalancer
ports:
# the port that this service should serve on
- port: 80
selector:
app: guestbook
tier: frontend
---
apiVersion: v1
kind: ReplicationController
metadata:
name: frontend
# these labels can be applied automatically
# from the labels in the pod template if not set
labels:
app: guestbook
tier: frontend
spec:
# this replicas value is default
# modify it according to your case
replicas: 3
# selector can be applied automatically
# from the labels in the pod template if not set
# selector:
# app: guestbook
# tier: frontend
template:
metadata:
labels:
app: guestbook
tier: frontend
spec:
containers:
- name: php-redis
image: corelab/gb-frontend:v5
resources:
requests:
cpu: 100m
memory: 100Mi
env:
- name: GET_HOSTS_FROM
value: dns
# If your cluster config does not include a dns service, then to
# instead access environment variables to find service host
# info, comment out the 'value: dns' line above, and uncomment the
# line below.
# value: env
ports:
- containerPort: 80
Install the Guestbook application:
root@kubemaster:~# kubectl create -f guestbook-all-in-one.yaml
Wait until all pods are in a READY state:
root@kubemaster:~# kubectl get pods -o wide NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES flask-cap 1/1 Running 0 53m 192.168.239.26 kubenode1.ittraining.loc <none> <none> flask-ro 1/1 Running 0 59m 192.168.150.14 kubenode2.ittraining.loc <none> <none> frontend-dhd4w 1/1 Running 0 32m 192.168.150.16 kubenode2.ittraining.loc <none> <none> frontend-dmbbf 1/1 Running 0 32m 192.168.150.17 kubenode2.ittraining.loc <none> <none> frontend-rqr6p 1/1 Running 0 32m 192.168.239.29 kubenode1.ittraining.loc <none> <none> redis-master-zrrr4 1/1 Running 0 32m 192.168.239.27 kubenode1.ittraining.loc <none> <none> redis-slave-jsrt6 1/1 Running 0 32m 192.168.150.15 kubenode2.ittraining.loc <none> <none> redis-slave-rrnx9 1/1 Running 0 32m 192.168.239.28 kubenode1.ittraining.loc <none> <none> ...
This application creates backend and frontend pods:
root@kubemaster:~# kubectl describe pod redis-master-zrrr4 | grep tier tier=backend root@kubemaster:~# kubectl describe pod frontend-dhd4w | grep tier tier=frontend
Create the guestbook-network-policy.yaml file that will prevent communication from a backend pod to a frontend pod:
To do: Copy the content from here and paste it into your file.
root@kubemaster:~# vi guestbook-network-policy.yaml
root@kubemaster:~# cat guestbook-network-policy.yaml
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
name: deny-backend-egress
namespace: default
spec:
podSelector:
matchLabels:
tier: backend
policyTypes:
- Egress
egress:
- to:
- podSelector:
matchLabels:
tier: backend
Run kubectl :
root@kubemaster:~# kubectl create -f guestbook-network-policy.yaml networkpolicy.networking.k8s.io/deny-backend-egress created
Connect to the redis-master pod:
root@kubemaster:~# kubectl exec -it redis-master-zrrr4 -- bash [ root@redis-master-zrrr4:/data ]$
Try to contact a pod of the same tier :
[ root@redis-master-zrrr4:/data ]$ ping -c 4 192.168.150.15 PING 192.168.150.15 (192.168.150.15) 56(84) bytes of data. 64 bytes from 192.168.150.15: icmp_seq=1 ttl=62 time=0.324 ms 64 bytes from 192.168.150.15: icmp_seq=2 ttl=62 time=0.291 ms 64 bytes from 192.168.150.15: icmp_seq=3 ttl=62 time=0.366 ms 64 bytes from 192.168.150.15: icmp_seq=4 ttl=62 time=0.379 ms --- 192.168.150.15 ping statistics --- 4 packets transmitted, 4 received, 0% packet loss, time 3070ms rtt min/avg/max/mdev = 0.291/0.340/0.379/0.034 ms
Now try to contact a pod on a tier frontend:
[ root@redis-master-zrrr4:/data ]$ ping -c 4 192.168.150.16 PING 192.168.150.16 (192.168.150.16) 56(84) bytes of data. --- 192.168.150.16 ping statistics --- 4 packets transmitted, 0 received, 100% packet loss, time 3063ms
Disconnect from the redis-master pod and connect to a frontend pod:
[ root@redis-master-zrrr4:/data ]$ exit exit command terminated with exit code 1 root@kubemaster:~# kubectl exec -it frontend-dhd4w -- bash root@frontend-dhd4w:/var/www/html#
Install the iputils-ping package:
root@frontend-dhd4w:/var/www/html# apt update root@frontend-dhd4w:/var/www/html# apt install iputils-ping -y
Try to contact a pod of the same tier :
root@frontend-dhd4w:/var/www/html# ping -c 4 192.168.150.17 PING 192.168.150.17 (192.168.150.17): 56 data bytes 64 bytes from 192.168.150.17: icmp_seq=0 ttl=63 time=0.185 ms 64 bytes from 192.168.150.17: icmp_seq=1 ttl=63 time=0.112 ms 64 bytes from 192.168.150.17: icmp_seq=2 ttl=63 time=0.093 ms 64 bytes from 192.168.150.17: icmp_seq=3 ttl=63 time=0.121 ms --- 192.168.150.17 ping statistics --- 4 packets transmitted, 4 packets received, 0% packet loss round-trip min/avg/max/stddev = 0.093/0.128/0.185/0.035 ms
Now try to contact a pod on a backend tier:
root@frontend-dhd4w:/var/www/html# ping -c 4 192.168.239.27 PING 192.168.239.27 (192.168.239.27): 56 data bytes 64 bytes from 192.168.239.27: icmp_seq=0 ttl=62 time=0.371 ms 64 bytes from 192.168.239.27: icmp_seq=1 ttl=62 time=0.469 ms 64 bytes from 192.168.239.27: icmp_seq=2 ttl=62 time=0.349 ms 64 bytes from 192.168.239.27: icmp_seq=3 ttl=62 time=0.358 ms --- 192.168.239.27 ping statistics --- 4 packets transmitted, 4 packets received, 0% packet loss round-trip min/avg/max/stddev = 0.349/0.387/0.469/0.048 ms
Exit the frontend pod:
root@frontend-dhd4w:/var/www/html# exit exit root@kubemaster:~#
2.4 - Kubernetes Resource Allocation Management
The resources that can be limited at the pod level are :
- CPU
- Memory
- Local storage
Create the file flask-resources.yaml:
To do: Copy the content from here and paste it into your file.
root@kubemaster:~# vi flask-resources.yaml
root@kubemaster:~# cat flask-resources.yaml
apiVersion: v1
kind: Pod
metadata:
name: flask-resources
namespace: default
spec:
containers:
- image: mateobur/flask
name: flask-resources
resources:
requests:
memory: 512Mi
limits:
memory: 700Mi
This file contains two resource allocations:
- requests,
- The amount of memory that must be free at the time of pod scheduling,
- limits,
- The memory limit for the pod concerned.
Run kubectl :
root@kubemaster:~# kubectl create -f flask-resources.yaml pod/flask-resources created
Wait until the pod status is READY :
root@kubemaster:~# kubectl get pods NAME READY STATUS RESTARTS AGE flask-cap 1/1 Running 0 67m flask-resources 1/1 Running 0 53s flask-ro 1/1 Running 0 74m ...
Connect to the pod :
root@kubemaster:~# kubectl exec -it flask-resources -- bash root@flask-resources:/#
Install the stress package:
root@flask-resources:/# echo “deb http://archive.debian.org/debian/ jessie main contrib non-free” > /etc/apt/sources.list root@flask-resources:/# echo “deb http://archive.debian.org/debian-security jessie/updates main contrib non-free” >> /etc/apt/sources.list root@flask-resources:/# cat /etc/apt/sources.list deb http://archive.debian.org/debian/ jessie main contrib non-free deb http://archive.debian.org/debian-security jessie/updates main contrib non-free root@flask-resources:/# apt update root@flask-resources:/# apt install stress -y
Test the limit:
root@flask-resources:/# stress --cpu 1 --io 1 --vm 2 --vm-bytes 800M stress: info: [41] dispatching hogs: 1 cpu, 1 io, 2 vm, 0 hdd stress: FAIL: [41] (416) <-- worker 45 got signal 9 stress: WARN: [41] (418) now reaping child worker processes stress: FAIL: [41] (452) failed run completed in 1s
Exit the flask-resources pod:
root@flask-resources:/# exit exit root@kubemaster:~#
Copyright © 2025 Hugh Norris
