1. What is a YAML file in Kubernetes?
YAML (YAML Ain't Markup Language) is a human-readable data serialization format used for configuration files. YAML files are commonly used to define Kubernetes resources such as pods, deployments, services, ReplicaSets, and more.
A YAML file consists of key-value pairs and lists, making it easy to represent hierarchical data structures. Kubernetes YAML files typically contain the following sections:
apiVersion: | Version of API. |
kind: | Kind of object you to create. |
metadata: | Name of object that uniquely identifies it. |
spec: | Desired state of the object. |
# kubectl get pod pod-nginx -o yaml
2.Yaml
file for pods.
apiVersion: v1
kind: Pod
metadata:
name: my-first-pod
labels:
app: my-app
spec:
containers:
- name: my-container
image: nginx:latest
ports:
- containerPort: 80
apiVersion: Specifies the API version being
used. In this case, it's v1, which is the most common version for pods.
kind: Specifies the type of Kubernetes
resource being defined. Here, it's Pod.
metadata: Contains metadata about the pod,
such as its name and labels.
name: Specifies the name of the pod.
labels: Specifies labels for the pod, which can be used for selecting and
grouping pods.
spec: Contains the specification of the
pod, including its containers.
containers: Specifies a list of containers to run in the pod.
name: Specifies the name of the container.
image: Specifies the Docker image to use for the container.
ports: Specifies a list of ports to expose from the container.
containerPort: Specifies the port number the container listens on.
More
details for Pods :-
https://kubernetes.io/docs/reference/kubernetes-api/workload-resources/pod-v1/
Detailed
information about Kubernetes resources.
# kubectl explain pods
https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.mdc
#
kubectl explain pods.spec
# kubectl explain
pods.spec.containers
What is
annotation in Kubernetes ?
Annotations
in Kubernetes (K8s) are metadata used to express additional information related
to a resource or object.
Annotations
consist of key-value pairs, each pair used to describe the resource’s metadata
or provide additional information. For example, it can be used to record a
resource’s creator, version, change history, relationship to a particular
component, and so on.
# cat first.yaml
apiVersion: apps/v1
kind: ReplicaSet
metadata:
name: test-replicaset
annotations:
developer: shashi@linux.com
spec:
replicas: 3
selector:
matchLabels:
tier: frontend
template:
metadata:
labels:
tier: frontend
spec:
containers:
- name: nginx-container
image: nginx
# kubectl describe rs test-replicaset
### Command and Arguments ###
command and arguments for a container
within a pod using the command and args fields in the container
specification.
Dockerfile
vs k8s Manifest perspective.
|
Docker Field Name |
Kubernetes Field name |
Description |
|
ENTRYPOINT |
command |
Command that will be run
by container. |
|
CMD |
args |
Argument passed to the
container. |
|
commands |
Arguments |
|
echo |
“Hello” |
|
sleep |
“3600” |
|
bash |
“demo.sh” |
Use case
-1
apiVersion:
v1
kind: Pod
metadata:
name: command
spec:
containers:
- name: count
image: busybox
command: ["sleep","3600"]
#
kubectl get pods
# kubectl
exec -it command sh
Use case
-2
apiVersion:
v1
kind: Pod
metadata:
name: command1
spec:
containers:
- name: count
image: busybox
command: ["sleep"]
args: ["3600"]
Use case
-3
apiVersion:
v1
kind: Pod
metadata:
name: command2
spec:
containers:
- name: count
image: busybox
args: ["sleep","3600"]
Use case
-4
run
multiple commands in a container
apiVersion:
v1
kind: Pod
metadata:
name: command2
spec:
containers:
- name: count
image: busybox
command: ["/bin/sh", "-c"]
args:
- |
echo "Executing the first command"
date
echo "Executing the second command"
printenv HOSTNAME
# kubectl
logs command2
