Kubernetes version 1.12.3. Does kubectl drain remove pod first or create pod first.
You can use kubectl drain to safely evict all of your pods from a node before you perform maintenance on the node (e.g. kernel upgrade, hardware maintenance, etc.)
When kubectl drain return successfuly it means it has removed all the pods successfully from that node and it is safe to bring that node down(physically shut off, or start maintainence)
Now if you turn on the machine and want to schedule pods again on that node you need to run:
kubectl uncordon <node name>
So, kubectl drain removes pods from the node and don't schedule any pods on that until you uncordon that node
kubectl drain will ignore certain system pods on the node that cannot be killed.
The given node will be marked unscheduled to prevent new pods from arriving.
When you are ready to put the node back into service, use kubectl uncordon, which will make the node schedulable again.
For for details use command:
kubectl drain --help
With this I hope you will get information which you are looking.
Related
Kubernetes nodes are getting unscheduled while i initiate the drain or cordon but the pods which is available on the node are not getting moved to different node immediately ?
i mean, these pods are not created by daemonset.
So, how come, Application running pod can make 100% available when a node getting faulty or with some issues ?
any inputs ?
command used :
To drain / cordon to make the node unavailable:
kubectl drain node1
kubectl cordon node1
To check the node status :
kubectl get nodes
To check the pod status before / after cordon or drain :
kubectl get pods -o wide
kubectl describe pod <pod-name>
Surprising part is , even node is unavailable, the pod status showing always running. :-)
Pods by itself doesn't migrate to another node.
You can use workload resources to create and manage multiple Pods for you. A controller for the resource handles replication and rollout and automatic healing in case of Pod failure. For example, if a Node fails, a controller notices that Pods on that Node have stopped working and creates a replacement Pod. The scheduler places the replacement Pod onto a healthy Node.
Some examples of controllers are:
deployment
daemonset
statefulsets
Check this link to more information.
If there is an update in the docker image, rolling update strategy will update all the pods one by one in a daemonset, similarly is it possible to restart the pods gracefully without any changes the daemonset config or can it be triggered explicitly?
Currently, I am doing it manually by
kubectl delete pod <pod-name>
One by one until each pod gets into running state.
You could try and use Node maintenance operations:
Use kubectl drain to gracefully terminate all pods on the node while marking the node as unschedulable (with --ignore-daemonsets, from Konstantin Vustin's comment):
kubectl drain $NODENAME --ignore-daemonsets
This keeps new pods from landing on the node while you are trying to get them off.
Then:
Make the node schedulable again:
kubectl uncordon $NODENAME
To trigger restart of all pods managed by deamonset in namespace [namespace_name]:
kubectl rollout restart de -n [namespace_name]
I have a running DaemonSet which is running on all nodes. I want to remove it from a node in order to completely drain it, as kubectl drain doesn't get rid of them. Without deleting my DaemonSet, what's a good way to temporarily remove those pods from the node? I've tried draining it and deleting the DaemonSet pods, but the DaemonSet will still reschedule them, disregarding that the node is set as Unschedulable: true.
You need to use --ignore-daemonsets key when you drain kubernetes node:
--ignore-daemonsets=false: Ignore DaemonSet-managed pods.
So, in order to drain kubernetes node with DaemonSets in cluster, you need to execute:
kubectl drain <node_name> --ignore-daemonsets
If you need to Remove DaemonSet pod from a node completely, you can specify a .spec.template.spec.nodeSelector in DaemonSet (the DaemonSet controller will create Pods on nodes which match that node selector) and set that label to all nodes except the one you need to completely drain.
How to delete all the contents from a kubernetes node? Contents include deployments, replica sets etc. I tried to delete deplyoments seperately. But kubernetes recreates all the pods again. Is there there any ways to delete all the replica sets present in a node?
If you are testing things, the easiest way would be
kubectl delete deployment --all
Althougth if you are using minikube, the easiest would probably be delete the machine and start again with a fresh node
minikube delete
minikube start
If we are talking about a production cluster, Kubernetes has a built-in feature to drain a node of the cluster, removing all the objects from that node safely.
You can use kubectl drain to safely evict all of your pods from a node before you perform maintenance on the node. Safe evictions allow the pod’s containers to gracefully terminate and will respect the PodDisruptionBudgets you have specified.
Note: By default kubectl drain will ignore certain system pods on the node that cannot be killed; see the kubectl drain documentation for more details.
When kubectl drain returns successfully, that indicates that all of the pods (except the ones excluded as described in the previous paragraph) have been safely evicted (respecting the desired graceful termination period, and without violating any application-level disruption SLOs). It is then safe to bring down the node by powering down its physical machine or, if running on a cloud platform, deleting its virtual machine.
First, identify the name of the node you wish to drain. You can list all of the nodes in your cluster with
kubectl get nodes
Next, tell Kubernetes to drain the node:
kubectl drain <node name>
Once it returns (without giving an error), you can power down the node (or equivalently, if on a cloud platform, delete the virtual machine backing the node). drain waits for graceful termination. You should not operate on the machine until the command completes.
If you leave the node in the cluster during the maintenance operation, you need to run
kubectl uncordon <node name>
afterwards to tell Kubernetes that it can resume scheduling new pods onto the node.
Please, note that if there are any pods that are not managed by ReplicationController, ReplicaSet, DaemonSet, StatefulSet or Job, then drain will not delete any pods unless you use --force, as mentioned in the docs.
kubectl drain <node name> --force
minikube delete --all
in case you are using minikube
it will let you start a new clean cluster.
in case you run on Kubernetes :
kubectl delete pods,deployments -A --all
it will remove it from all namespaces, you can add more objects in the same command .
Kubenertes provides namespaces object for isolation and separation of concern. Therefore, It is recommended to apply all of the k8s resources objects (Deployment, ReplicaSet, Pods, Services and other) in a custom namespace.
Now If you want to remove all of the relevant and related k8s resources, you just need to delete the namespace which will remove all of these resources.
kubectl create namespace custom-namespace
kubectl create -f deployment.yaml --namespace=custom-namespace
kubectl delete namespaces custom-namespace
I have attached a link for further research.
Namespaces
I tried so many variations to delete old pods from tutorials, including everything here.
What finally worked for me was:
kubectl delete replicaset --all
Deleting them one at a time didn't seem to work; it was only with the --all flag that all pods were deleted without being recreated.
I want to scale up/down the number of machines to increase/decrease the number of nodes in my Kubernetes cluster. When I add one machine, I’m able to successfully register it with Kubernetes; therefore, a new node is created as expected. However, it is not clear to me how to smoothly shut down the machine later. A good workflow would be:
Mark the node related to the machine that I am going to shut down as unschedulable;
Start the pod(s) that is running in the node in other node(s);
Gracefully delete the pod(s) that is running in the node;
Delete the node.
If I understood correctly, even kubectl drain (discussion) doesn't do what I expect since it doesn’t start the pods before deleting them (it relies on a replication controller to start the pods afterwards which may cause downtime). Am I missing something?
How should I properly shutdown a machine?
List the nodes and get the <node-name> you want to drain or (remove from cluster)
kubectl get nodes
1) First drain the node
kubectl drain <node-name>
You might have to ignore daemonsets and local-data in the machine
kubectl drain <node-name> --ignore-daemonsets --delete-local-data
2) Edit instance group for nodes (Only if you are using kops)
kops edit ig nodes
Set the MIN and MAX size to whatever it is -1
Just save the file (nothing extra to be done)
You still might see some pods in the drained node that are related to daemonsets like networking plugin, fluentd for logs, kubedns/coredns etc
3) Finally delete the node
kubectl delete node <node-name>
4) Commit the state for KOPS in s3: (Only if you are using kops)
kops update cluster --yes
OR (if you are using kubeadm)
If you are using kubeadm and would like to reset the machine to a state which was there before running kubeadm join then run
kubeadm reset
Find the node with kubectl get nodes. We’ll assume the name of node to be removed is “mynode”, replace that going forward with the actual node name.
Drain it with kubectl drain mynode
Delete it with kubectl delete node mynode
If using kubeadm, run on “mynode” itself kubeadm reset
Rafael. kubectl drain does work as you describe. There is some downtime, just as if the machine crashed.
Can you describe your setup? How many replicas do you have, and are you provisioned such that you can't handle any downtime of a single replica?
If the cluster is created by kops
1.kubectl drain <node-name>
now all the pods will be evicted
ignore daemeondet:
2.kubectl drain <node-name> --ignore-daemonsets --delete-local-data
3.kops edit ig nodes-3 --state=s3://bucketname
set max and min value of instance group to 0
4. kubectl delete node
5. kops update cluster --state=s3://bucketname --yes
Rolling update if required:
6. kops rolling-update cluster --state=s3://bucketname --yes
validate cluster:
7.kops validate cluster --state=s3://bucketname
Now the instance will be terminated.
The below command only works if you have a lot of replicas, disruption budgets, etc. - but helps a lot with improving cluster utilization. In our cluster we have integration tests kicked off throughout the day (pods run for an hour and then spin down) as well as some dev-workload (runs for a few days until a dev spins it down manually). I am running this every night and get from ~100 nodes in the cluster down to ~20 - which adds up to a fair amount of savings:
for node in $(kubectl get nodes -o name| cut -d "/" -f2); do
kubectl drain --ignore-daemonsets --delete-emptydir-data $node;
kubectl delete node $node;
done
Remove worker node from Kubernetes
kubectl get nodes
kubectl drain < node-name > --ignore-daemonsets
kubectl delete node < node-name >
When draining a node we can have the risk that the nodes remain unbalanced and that some processes suffer downtime. The purpose of this method is to maintain the load balance between nodes as much as possible in addition to avoiding downtime.
# Mark the node as unschedulable.
echo Mark the node as unschedulable $NODENAME
kubectl cordon $NODENAME
# Get the list of namespaces running on the node.
NAMESPACES=$(kubectl get pods --all-namespaces -o custom-columns=:metadata.namespace --field-selector spec.nodeName=$NODENAME | sort -u | sed -e "/^ *$/d")
# forcing a rollout on each of its deployments.
# Since the node is unschedulable, Kubernetes allocates
# the pods in other nodes automatically.
for NAMESPACE in $NAMESPACES
do
echo deployment restart for $NAMESPACE
kubectl rollout restart deployment/name -n $NAMESPACE
done
# Wait for deployments rollouts to finish.
for NAMESPACE in $NAMESPACES
do
echo deployment status for $NAMESPACE
kubectl rollout status deployment/name -n $NAMESPACE
done
# Drain node to be removed
kubectl drain $NODENAME
There exists some strange behaviors for me when kubectl drain. Here are my extra steps, otherwise DATA WILL LOST in my case!
Short answer: CHECK THAT no PersistentVolume is mounted to this node. If have some PV, see the following descriptions to remove it.
When executing kubectl drain, I noticed, some Pods are not evicted (they just did not appear in those logs like evicting pod xxx).
In my case, some are pods with soft anti-affinity (so they do not like to go to the remaining nodes), some are pods of StatefulSet of size 1 and wants to keep at least 1 pod.
If I directly delete that node (using the commands mentioned in other answers), data will get lost because those pods have some PersistentVolumes, and deleting a Node will also delete PersistentVolumes (if using some cloud providers).
Thus, please manually delete those pods one by one. After deleted, kuberentes will re-schedule the pods to other nodes (because this node is SchedulingDisabled).
After deleting all pods (excluding DaemonSets), please CHECK THAT no PersistentVolume is mounted to this node.
Then you can safely delete the node itself :)