I understand that the nodeSelector will help to move the pods to specific nodes with labels. But, say if I know the names for pods in advance and based on these names, how do I move these pods to different nodes having specific labels.
I am unable to understand as to how to use nodeSelector, affinity, antiAffinity in this case.
What would an example values.yaml look like?
I have labelled three nodes. Then, when I launch the 6 pods, they are equally divided among the nodes. Each pod has an index value at the end of the pod name. mypod-0, mypod-1 until mypod-5.
I want to have mypod-0 and mypod-3 on node 1, mypod-1 and mypod-4 on node 2 and so on.
We can use Pod Topology Constraints to decide how the pods need to spread across your cluster.
For Example as per you question we can deploy 2 pods in 1 node and other 2 pods in different node. To make this possible we need to set the topologyKey for nodes and use them while deploying the pod. This sample yaml shows the syntax of pod topology constraints.
kind: Pod
apiVersion: v1
metadata:
name: mypod
labels:
foo: bar
spec:
topologySpreadConstraints:
- maxSkew: 1
topologyKey: zone
whenUnsatisfiable: DoNotSchedule
labelSelector:
matchLabels:
foo: bar
containers:
- name: nginx
image: nginx
Since you are using labels for naming the pods you can use nodeAffinity and nodeSelectors along with pod topology constraints. For more information regarding the combination of topology and affinity refer to this official k8 document
Related
I have 4 node with different zone:
Node A : zone a
Node B : zone b
Node C : zone c
Node D : zone c
I want to spread the pod to Node A, B and C. I have Deployment that have 3 replicas to spread across those node, each pod each node. My deployments using kustomization and ArgoCD to deploy. Using the topologySpreadConstraint need to be update the label but labels are immutable on this case.
Current deployment condition using this
apiVersion: apps/v1
kind: Deployment
metadata:
name: my-apps
spec:
replicas: 3
revisionHistoryLimit: 0
template:
spec:
affinity:
nodeAffinity:
requiredDuringSchedulingIgnoredDuringExecution:
nodeSelectorTerms:
- matchExpressions:
- key: app
operator: In
values:
- my-apps
topologySpreadConstraints:
- maxSkew: 1
topologyKey: topology.kubernetes.io/zone
whenUnsatisfiable: DoNotSchedule
labelSelector:
matchLabels:
app: my-apps
version: v1
...
I've done add label for those 3 nodes and this configuration works well at first time. But when it comes to update the deployment and rolling update, The pods on nodes going to imbalance.
zone a : 2 pod
zone b : 1 pod
zone c : 0 pod
I've done playing with podAntiAffinity but its return as pending if I use hard affinity and still imbalance if I use soft affinity. Any suggestion best practice for this case? did I missed something?
Rolling updates cause some pods to be removed from nodes and others to be added. This can cause the pods on nodes to become imbalanced, as the pods that were already on the nodes will remain, but the pods that are added during the update will likely be different. To prevent this from happening, it is important to use the maxUnavailable option in the rolling update strategy. This allows you to specify the maximum number of pods that can be removed from a node during the rolling update, ensuring that the pods on each node remain balanced.
kubectl apply -f deployment.yaml --strategy=RollingUpdate --strategy-rolling-update-maxUnavailable=1
This command will create or update a deployment with the rolling update strategy, and the maxUnavailable option set to 1.This will ensure that no more than 1 pod is removed from a node during the rolling update, thus keeping the pods across nodes balanced.Try it and let me know if this works
If you are scaling down the pods, as per official doc limitations:
There's no guarantee that the constraints remain satisfied when Pods are removed. For example, scaling down a Deployment may result in an imbalanced Pods distribution.You can use a tool such as the Descheduler to rebalance the Pods distribution.
I'm trying to understand, if it is possible ( and how ) to pin pods of statefulsets to specific availibility zones. In the example above I would like to explicitly configure, that elastic pod 1 runs in availibility zone 1, pod 2 in availibility zone 2 and so forth. I also don't want the pods to run outside of their availibility zones, if one goes down.
I read this doc on the matter. If I understand it correctly, I can only specify, that a statefulset shouldn't run it's pods in the same availibility zone, but not, that it always runs the pod in a specific availibility zone.
Thanks to anyone who can educate me in this matter.
aws overview
You can use Pod Topology Spread constraints.
topology spread constraints control how Pods are spread across your
cluster among failure-domains such as regions, zones, nodes, and other
user-defined topology domains. This can help to achieve high
availability as well as efficient resource utilization.
Taking the example from here
kind: Pod
apiVersion: v1
metadata:
name: mypod
labels:
foo: bar
spec:
topologySpreadConstraints:
- maxSkew: 1
topologyKey: zone
whenUnsatisfiable: DoNotSchedule
labelSelector:
matchLabels:
foo: bar
containers:
- name: pause
image: k8s.gcr.io/pause:3.1
In my GKE Kubernetes cluster, I have 2 node pools; one with regular nodes and the other with pre-emptible nodes. I'd like some of the pods to be on pre-emptible nodes so I can save costs while I have at least 1 pod on a regular non-pre-emptible node to reduce the risk of downtime.
I'm aware of using podAntiAffinity to encourage pods to be scheduled on different nodes, but is there a way to have k8s schedule pods for a single deployment across both pools?
Yes 💡! You can use Pod Topology Spread Constraints, based on a label 🏷️ key on your nodes. For example, the label could be type and the values could be regular and preemptible. Then you can have something like this:
kind: Pod
apiVersion: v1
metadata:
name: mypod
labels:
foo: bar
spec:
topologySpreadConstraints:
- maxSkew: 1
topologyKey: type
whenUnsatisfiable: DoNotSchedule
labelSelector:
matchLabels:
foo: bar
containers:
- name: app
image: myimage
You can also identify a maxSkew which means the maximum differentiation of a number of pods that one label value (node type) can have.
You can also combine multiple 'Pod Topology Spread Constraints' and also together with PodAffinity/AntiAffinity and NodeAffinity. All depending on what best fits your use case.
Note: This feature is alpha in 1.16 and beta in 1.18. Beta features are enabled by default but with alpha features, you need an alpha cluster in GKE.
☮️✌️
i need to isolate dedicated node for monitoring on our Kubernetes cluster anybody know what is the best practise for that?so that it is not impacted by auto scaling
Yes this can be achieved, that's where Labels and Selectors come in handy.
You can label your nodes with key/value pairs, in-order to isolate your nodes based on behaviour of your application, Node isoloation/restriction.
There are several ways one can label their nodes. But this the common and simplest example.
kubectl label nodes <node-name> <label-key>=<label-value>
Eg: kubectl label nodes k8-node-101 instance-type=monitoring
And in your deployment make sure you add the nodeSelector, something like this.
apiVersion: v1
kind: Pod
metadata:
name: monitoring-pod
spec:
containers:
- name: mon-test
image: "cr.mycompany.io/monitoring:v0.1"
nodeSelector:
instance-type: monitoring
This is one example on how you can isolate your node for specific needs or specific project purposes.
Hope this helps.
How can I configure a specific pod to run on a multi-node kubernetes cluster so that it would restrict the containers of the POD to a subset of the nodes.
E.g. let's say I have A, B, C three nodes running mu kubernetes cluster.
How to limit a Pod to run its containers only on A & B, and not on C?
You can add label to nodes that you want to run pod on and add nodeSelector to pod configuration. The process is described here:
http://kubernetes.io/docs/user-guide/node-selection/
So basically you want to
kubectl label nodes A node_type=foo
kubectl label nodes B node_type=foo
And you want to have this nodeSelector in your pod spec:
nodeSelector:
node_type: foo
Firstly, you need to add label to nodes. You can refer to Nebril's answer of how to add label.
Then I recommend you to use the node affinity feature to constrain pods to nodes with particular labels. Here is an example.
apiVersion: v1
kind: Pod
metadata:
name: with-node-affinity
spec:
affinity:
nodeAffinity:
requiredDuringSchedulingIgnoredDuringExecution:
nodeSelectorTerms:
- matchExpressions:
- key: node_type
operator: In
values:
- foo
containers:
- name: with-node-affinity
image: gcr.io/google_containers/pause:2.0
Compared to nodeSelector, the affinity/anti-affinity feature greatly expands the types of constraints you can express.
For more detailed information about node affinity, you can refer to the following link: https://kubernetes.io/docs/concepts/configuration/assign-pod-node/
I am unable to post a comment to previous replies but I upvoted the answer that is complete.
nodeSelector is not strictly enforced and relying on it may cause some grief including Master getting overwhelmed with requests as well as IOs from pods scheduled on Master. At the time the answer was provided it may still have been the only option but in the later versions that is not so.
Definitely use nodeAffinity or nodeAntiAffinity with requiredDuringSchedulingIgnoredDuringExecution or preferredDuringSchedulingIgnoredDuringExecution
For more expressive filters for scheduling peruse: Assigning pods to nodes