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Hi, Let us have a quick understanding on selector operator. In many of the objects

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like deployments, replica sets or even services we will be using the selector to

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select any specific object using the labels and there are different

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combinations we can provide to select the objects. For understanding purpose

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I'm going to deploy an application and use the selector to select the pods to

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understand how different ways we can use the selectors. Let me go ahead and

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use a yaml file that's available as a part of kubernetes samples. Here there is a

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yaml file all in one guest book where it is going to deploy 3 different services and

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deployments, say for example I am going to have a service called redis master

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that's going to have different labels and a deployment for redis master at the

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same way I'm going to have another service for redis-slave and deployment

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for redis slave and deployment for frontend, it's going to have different

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labels, I'm going to use this specific yaml file and get this deployed within the

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kubernetes. Let me use the command kubectl apply, then the file path you can

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read directly from the github user content and automatically it's going to

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create the service and deployment. Now let me go ahead and get the deployments I can

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say kubectl get deployment and get services, so I should have the details

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about the service and the deployments, all the deployments are in readystate the

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required capacity it got deployed. Now I can use the get pods option and use the

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selector. Now I am going to get all the pods kubectl get pods and I want the

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labels to get displayed for each and every pods, so I'll use the option show labels. So

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that's going to have the labels attached to those pods like

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app guest book, app nginx, app redis, so all the labels will get displayed. Now

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I am going to get the pods with what are all the labels attached to what pods. So

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I'm going to list the pods with the label app tier and role, for few minutes let me

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reduce the font so that I will be getting each and every item in a single row. So

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the app what is the value that's used, that'll get listed over here and for tier

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what is the role that is used and for role what is the value that was used. Now let

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me go ahead and verify the yaml file, here I do have different labels like app

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tier, role and this is what we are listing what value was assigned to that specific

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pod and what is the label. So I am trying to list the value for the label app, label tier

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and label role. So this is another way of listing the pods now I can go ahead and

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use the selector where app is redis. So I'm selecting all the pods where the app is

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redis, so it's going to get all the pods where app is redis, so I do have 3 pods

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with the label app is redis. Now I can go ahead and have another combination

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where app is redis and role is slave, so I do have 2 pods with app is redis and role

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as slaves and I can go for the collections as well, where role in master or slave. So I'll be

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having both the combinations and all the pods meeting this specific condition will

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get selected. I can even go for the negative conditions where it doesn't have

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the app label. so here I do have all the pods where the app label is set, now I am

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going to get all the pods where app label is not set. So I am using the selector not

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that is exclamatory mark and then app, so there is no resources

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available in case if there were any resources that will get selected. Maybe

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I can go ahead and create a sample pod and check whether that is getting

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selected or not. So I am going to run a pod with a name nginx run with a image

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nginx. Now let me go ahead and use the exclamatory mark where it doesn't have

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a label app, of course the new pod that we created we did not set the label app

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so it's getting selected for this specific condition. So the selector we will be using

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it extensively to pick the pod that we wanted to act on as there will be

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hundreds and hundreds of pods and other objects running within the

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kubernetes cluster, whenever there is a need to pick a group of pods I will be

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using this particular label to pick the pods and take the actions like deploying

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them or terminating them or in case if I wanted to scale up scale down n number

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of actions I can do. So basically the labels will be used to select where the

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pod should run, how the pod should run, what action to be taken against what set

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of pods, in lot more places we will be using it. So this is the quick summary on

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how we can use the selectors what are all different types of combinations and

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of course lot more combinations can be used these are all the

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frequently used to combinations while using the label selector.