I am going to implement PDB on AKS. Can someone please tell me why do we need it when we can use node autoscaler.
Also, does PDB allow zero unavailability by creating a node when one of the nodes fails?
PDB allows you to set rules before evicting your pods from a node.
Let's say you have a 2 nodes cluster and a deployment with 1 replica and you want to update your nodes.
kubectl drain will cordon node 1 so no pods can be schedule on that node
kubectl drain will remove the pod schedule on node 1
kubelet will then deploy your pod over node 2
Now if you set a PDB with a minAvailable: 50%, that drain command would fail as it would violates the rule.
The pods is killed and then kubelet tries to schedule it somewhere.
PDB allows you to prevent downtime by budgeting pods before evicting them.
Scenario without PDB
You perform node 1 update and node 2 cannot host the evicted pod :
pod is killed on node 1
kubelet cannot schedule pod anywhere
autoscaling provisions a third node
pod is scheduled on that new node
During that whole time your evicted pod was not running anywhere and your application was down.
One worker node was powered off, get node status by kubectl get nodes shows that node is NotReady.
But kubectl get po -o wide --all-namespaces|egrep 'daemonSet-pod|node-hostname', it shows some DaemonSet pods still running on NotReady node and cannot connect to these pods.
Why Daemonset pod still show Running even if the node NotReady?
After kubernetes version 1.13, Tolerations like node.kubernetes.io/not-ready are added automatically to DaemonSets. That means DaemonSet pods will not be evicted when there are node problems like you describe.
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.
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 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 :)