Table of Contents
Most developers make the mistake of using the base image out-of-the-box, which may have up to 80% of packages and libraries they don’t need.
Always use smaller container images as it helps you to create faster builds. As a best practice, you should:
- Go for Alpine Images, as they are 10x smaller than the base images
- Add necessary libraries and packages as required for your application. Smaller images are also less susceptible to attack vectors due to a reduced attack surface.
- By default, there are three different namespaces in Kubernetes in the beginning: default, kube-public and kube-system. For example, you should create different namespaces for development, testing and production teams. This way, the developer having access to only the development namespace won’t be able to make any changes in the production namespace, even by mistake.
apiVersion: v1
kind: Pod
metadata:
name: development
namespace: development
labels:
image: development01
spec:
containers:
- name: development01
image: nginx
In Kubernetes, probes are managed by the kubelet. The kubelet performs periodic diagnostics on containers running on the node. In order to support these diagnostics, a container must implement one of the following handlers:
- ExecAction handler—runs a command inside the container, and the diagnostic succeeds if the command completes with status code 0.
- TCPSocketAction handler—attempts a TCP connection to the IP address of the pod on a specific port. The diagnostic succeeds if the port is found to be open.
- HTTPGetAction handler—performs an HTTP GET request, using the IP address of the pod, a specific port, and a specified path. The diagnostic succeeds if the response code returned is between 200-399.
-
Readiness probe A readiness probe indicates whether the application running on the container is ready to accept requests from clients:
- If it succeeds, services matching the pod continue sending traffic to the pod
- If it fails, the endpoints controller removes the pod from all Kubernetes Services matching the pod
-
Liveness probe A liveness probe indicates if the container is operating:
- If it succeeds, no action is taken and no events are logged
- If it fails, the kubelet kills the container, and it is restarted in line with the pod restartPolicy
-
Startup probe A startup probe indicates whether the application running in the container has fully started:
- If it succeeds, other probes start their diagnostics. When a startup probe is defined, other probes do not operate until it succeeds
- If it fails, the kubelet kills the container, and is restarted in line with the pod restartPolicy
In this example, the probe pings an application to check if it is still running. If it gets the HTTP response, it then marks the pod as healthy.
apiVersion: apps/v1
kind: Deployment
metadata:
name: readiness-example
spec:
...
spec:
containers:
- name: readiness-example
image: dbdock/readiness-example:1.0.0
...
readinessProbe:
httpGet:
path: /health
port: 8080
initialDelaySeconds: 40
timeoutSeconds: 2
periodSeconds: 3
failureThreshold: 2
livenessProbe:
httpGet:
path: /health
port: 8080
initialDelaySeconds: 100
timeoutSeconds: 2
periodSeconds: 8
failureThreshold: 1
initialDelaySeconds : How much time after health checks will be start
timeoutSeconds : How long to wait for the response of your request
periodSeconds : How long will these requests be forwarded for testing
successThreshold : After how many successful requests will it be considered successful
failureThreshold : After hoy many failed requests will it be considered unsuccessful
-
Occasionally deploying an application to a production cluster can fail due limited resources available on that cluster. This is a common challenge when working with a Kubernetes cluster and it’s caused when resource requests and limits are not set. Without resource requests and limits, pods in a cluster can start utilizing more resources than required. If the pod starts consuming more CPU or memory on the node, then the scheduler may not be able to place new pods, and even the node itself may crash.
-
Resource requests specify the minimum amount of resources a container can use
-
Resource limits specify the maximum amount of resources a container can use.
In this example, we have set the limit of CPU to 800 millicores and memory to 256 mebibytes. The maximum request which the container can make at a time is 400 millicores of CPU and 128 mebibyte of memory.
containers:
- name: container1
image: busybox
resources:
requests:
memory: “128Mi”
cpu: “400m”
limits:
memory: “256Mi”
cpu: “800m”
-
The CPU is known as a compressible resource, so when your application withstands these CPU limits, k8s will start throttling the application's CPU usage, so that only the performance of the application will decrease. The application will not be terminated.
-
However, since Memory is not a compressible resource, the application will be terminated when it reaches or exceeds the given limit.
- For example, let’s say you are running two instances of one type of application. Both are similarly named, but each application is used by different teams (e.g., development and testing). You can help your teams differentiate between the similar applications by defining a label which uses their team’s name to demonstrate ownership.
apiVersion: v1
kind: Pod
metadata:
name: ops-pod
labels:
environment: operations
team: ops01
spec:
containers:
- name: ops01
image: "Ubuntu"
resources:
limits:
cpu: 1
-
Role-based access control (RBAC) is an approach used to restrict access and admittance to users and applications on the system or network. An RBAC Role or ClusterRole contains rules that represent a set of permissions. Permissions are purely additive (there are no "deny" rules).
-
A Role always sets permissions within a particular namespace; when you create a Role, you have to specify the namespace it belongs in.
-
ClusterRole, by contrast, is a non-namespaced resource. The resources have different names (Role and ClusterRole) because a Kubernetes object always has to be either namespaced or not namespaced; it can't be both.
-
if you want to define a role within a namespace, use a Role; if you want to define a role cluster-wide, use a ClusterRole.
Role example
apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
namespace: default
name: pod-reader
rules:
- apiGroups: [""] # "" indicates the core API group
resources: ["pods"]
verbs: ["get", "watch", "list"]
ClusterRole example
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
# "namespace" omitted since ClusterRoles are not namespaced
name: secret-reader
rules:
- apiGroups: [""]
#
# at the HTTP level, the name of the resource for accessing Secret
# objects is "secrets"
resources: ["secrets"]
verbs: ["get", "watch", "list"]
- It is strongly recommended that you leverage benefits from Kubernetes' autoscaling mechanisms to automatically scale cluster services with a surge in resource consumption. With Horizontal Pod Autoscaler and Cluster Autoscaler, node and pod volumes get adjusted dynamically in real-time, thereby maintaining load to the optimum level and avoiding capacity downtimes.