Kubernetes in practice
Annotations
- Kubernetes provide us annotation feature with labels.
- Annotations are basically words that explanations or comments on something.
- For example, annotation can be used to write creator’s name or contact or about application it running.
- Labels are meant to hold limited information whereas we can have larger annotation with any resource.
- Annotations are way to add some extra information to the resource but it cannot be used to group or filter like labels.
Overlapping Labels
- With labels it is easy is to group resources.
- But what if any label overlap, for example
- type = frontend is assigned to few pods with app_name_web and env_development
- type = frontend is assigned to few pods with app_name_web and env_development
- Name of particular resource will always be unique, what about setting the similar environment as production with in development, QA phase.
- But what about times when you wan to split objects in separate, non-overlapping groups? We may want to only operate inside one group at a time.
Namespace
- Kubernetes also groups objects into namespaces.
- Namespace is kind of virtual box which isolate self contain resources with other namespace.
- We can easily separate the scope of resources using namespaces.e.g Resource in namespace for development phase cannot harm resources in namespace for production.
- Similarly we can split them into multiple namespaces, which also allows us to use the same resource names multiple times (across different namespaces)
Creating namespace
- Kubectl create namespace production
- Kubectl get ns
- Kubectl create ns development
- Kubectl get ns
Pod inside namespace
- nano myfirstpod.yaml
- Kubectl create -f myfirstpod.yaml
- Kubectl get pods –namespace = production
- Kubectl run nsexample –image = ahmedmansoor/helloworld –port = 80 –restart = Never –namespace = development
- Kubectl get pods
- Kubectl get pods -n production
- Kubectl get pods -n development
Listing pod from All Namespaces
- Kubectl get pods — all-namespaces
Deleting Resource
- Kubectl delete pod myfirstpod
- Kubectl get pods –all-namespaces
- Kubectl delete pod myfirstpod –namespace = production
- Kubectl delete ns development
- kubectl get ns
- Kubectl get pod — show-labels
- Kubectl delete pods-l type = backend
- Kubectl delete pod –all
Replica Sets
- Replica set is also one of the resource in Kubernetes like pods and others are.It is often used to guarantee the availability of a specified number of identical Pods.
- Replica set is the resource that help creating and managing multiple copies of application (replicas) in Kubernetes.
- When we create any pod through Replica set it ensures its pods are always kept running.
- If the pod removes for any reason, such as
- if the worker node disappears from the cluster
- If the pod was evicted from the worker node
- The replica set notes the missing pod and creates a replacement pod.