# Labels and Node Selector in Kubernetes Labels in Kubernetes are the key-value pair that does not have any predefined meaning and that can be attached to any objects or any resources such as Pod, Deployment, or Node which is mainly used to identify and organize Kubernetes resources. We could add an 'environment' label to a set of pods with the value 'production' and 'development' to other sets of pods. We could then use label selectors to select only the pods in the 'production' environment. The label is defined under the metadata field with 'labels' as a field. Multiple labels can be added to a single object. Let us take an example of creating a label. ```bash vi label-pod.yml ``` ```yaml kind: Pod apiVersion: v1 metadata: name: label-first-pod labels: env: developments class: pods spec: containers: - name: label-container image: ubuntu command: ["/bin/bash","-c","while true; do echo this-is-lable-pod; sleep 5; done"] ``` Now apply the above configuration ```bash kubectl apply -f label-pod.yml ``` Get labels on all the pods ```bash kubectl get pods --show-lables ``` If we want to add a label to an existing pod `kubectl label pods ` In our case, it would be something like ```bash kubectl label pods label-first-pod myname=sandeep ``` Here myname will be added as a label with the value of sandeep in the pod label-first-pod To see the labels of all the pod ```bash kubectl get pods --show-labels ``` Now list pods matching a label ```bash kubectl get pods -l env=developments ``` List pods where the 'developments' label is not present ```bash kubectl get pods -l env!=developments ``` Now delete the pod ```bash kubeclt delete -f label-pod.yml ``` # Labels Selectors The label selectors are the filter to narrow down resources based on their labels. As the name suggests, it is used to select specific pods to perform the action. It may be to specify pods to be included in a service, to be managed by deployment or rollout, or to be scaled by a horizontal pod scaler. The API currently supports two types of selectors 1. Equality Based: They are the kind of selectors that matches resources that have a label with a specific key and value. For example, the selector “env=development” would match any resource with the label “env=development”. We can also specify multiple selectors by separating them with a comma. For example, “env=development, myname=sandeep”. 2. Set Based: The set selectors match multiple values based on a set of values for a key. There are mainly three types of set-based selectors: 1. {key} in {values}. For example ‘environment in (production, development). It matches with a label ‘environment’ that has either production or development. It matches either production or development. 2. {key} notin {values}. For example ‘environment notion (production, development). It matches neither production nor development. 3. {key} For example, ‘environment’, matches resources with a label ‘environment’ that has any value. Example of Equality Based selector ```bash kubectl get pods -l class=pods, myname=sandeeep ``` Example of a Set Based selector ```bash kubectl get pods -l 'env in (development, testing)' ``` ## Node selector When we create a pod, the master node randomly assigns a node to it. If we want to assign a specific node to a pod then we use 'nodeSelector'. One use case for selecting labels is to constrain the set of nodes onto which a pod can schedule i.e. you can tell apod to only be able to run on a particular node. Generally, such constraints are unnecessary as the scheduler will always automatically do a reasonable placement, but in certain circumstances, we might need it. We can use labels to tag nodes and use label selectors to specify the pods to run on specific nodes. For this purpose, first, we give a label to the node, and then we use a node selector for the pod configuration. For labeling the nodes ```bash kubectl get nodes ``` `kubectl label nodes ip-xxx-xxx-xxx-xxx