14-DAEMON SETS

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DAEMON SETS - when we use repicaset it makes sure an specified number of copies of pods exist in the cluster but the node the replica exists doesnt matter but when we use DAEMON SETS it makes sure one copy of a pod run on all the nodes, if a new node is added then replica of the pod will be deployed on the new node too.

use case  - to monitor the nodes that are in the cluster
		  - to collect the logs of nodes in the cluster
example yaml for daemon set (cat > daemonset-definition.yaml)-
piVersion: apps/v1
kind: DaemonSet
metadata:
   name:monitorining-daemon(this is name of daemonset)
   labels:
      app: my-app
      costCenter: US   

spec:
   selector:
      matchLabels:
	     app:monitoring-agent
   template:
      metadata:
	     labels:
		    app:montioring-agent
      spec:
         containers:
            - name:monitoring-agent
              image:monitoring-agent
		    
This is yaml is exactly like replicaset only change is kind which is DaemonSet instead of ReplicaSet

pods deployed by the daemonset will have the same name as daemonset

command- kubectl create -f daemonset-definition.yaml
to view daemonstes command- kubectl get daemonsets
to view more datials - kubectl describe daemonsets <daemonset name>

command to get daemosnsets in all namespaces - kubectl get ds --all-namespaces
command to see the nodes on which the daemonset is ruinng - kubectl -n <namespace name> get pods -o wide |grep <daemonset name>
command to see the image that daemonset uses - kubectl -n <namespace name> descibe -ds <daemonset name> |grep -i image

another way to create daemonset - kubectl create deployment <daemonset name> --image=<imagename> --dry-run=client -o yaml >daemon-set.yaml
do the required changes to the yaml to convert it into daemonset yaml and run kubectl apply -f daemon-set.yaml

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