I was trying to make file before application gets up in kubernetes cluster with initcontainers,
But when i am setting up the pod.yaml and trying to apply it with "kubectl apply -f pod.yaml" it throws below error
error-image
Like the error says, you cannot update a Pod adding or removing containers. To quote the documentation ( https://kubernetes.io/docs/concepts/workloads/pods/#pod-update-and-replacement )
Kubernetes doesn't prevent you from managing Pods directly. It is
possible to update some fields of a running Pod, in place. However,
Pod update operations like patch, and replace have some limitations
This is because usually, you don't create Pods directly, instead you use Deployments, Jobs, StatefulSets (and more) which are high-level resources that defines Pods templates. When you modify the template, Kubernetes simply delete the old Pod and then schedule the new version.
In your case:
you could delete the pod first, then create it again with the new specs you defined. But take into consideration that the Pod may be scheduled on a different node of the cluster (if you have more than one) and that may have a different IP Address as Pods are disposable entities.
Change your definition with a slightly more complex one, a Deployment ( https://kubernetes.io/docs/concepts/workloads/controllers/deployment/ ) which can be changed as desired and, each time you'll make a change to its definition, the old Pod will be removed and a new one will be scheduled.
From the spec of your Pod, I see that you are using a volume to share data between the init container and the main container. This is the optimal way but you don't necessarily need to use a hostPath. If the only needs for the volume is to share data between init container and other containers, you can simply use emptyDir type, which acts as a temporary volume that can be shared between containers and that will be cleaned up when the Pod is removed from the cluster for any reason.
You can check the documentation here: https://kubernetes.io/docs/concepts/storage/volumes/#emptydir
Related
I have used some bitnami charts in my kubernetes app. In my pod, there is a file whose path is /etc/settings/test.html. I want to override the file. When I search it, I figured out that I should mount my file by creating a configmap. But how can I use the created configmap with the existed pod . Many of the examples creates a new pod and uses the created config map. But I dont want to create a new pod, I wnat to use the existed pod.
Thanks
If not all then almost all pod specs are immutable, meaning that you can't change them without destroying the old pod and creating a new one with desired parameters. There is no way to edit pod volume list without recreating it.
The reason behind this is that pods aren't meant to be immortal. Pods meant to be temporary units that can be spawned/destroyed according to scheduler needs. In general, you need a workload object that does pod management for you (a Deployement, StatefulSet, Job, or DaemonSet, depenging on deployment strategy and application nature).
There are two ways to edit a file in an existing pod: either by using kubectl exec and console commands to edit the file in place, or kubectl cp to copy an already edited file into the pod. I advise you against both of these, because this is not permanent. Better backup the necessary data, switch deployment type to Deployment with one replica, then go with mounting a configMap as you read on the Internet.
Does anyone know how to delete pod from kubernetes master node? I have this one master node on bare-metal ubuntu server. When i'm trying to delete it with "kubectl delete pod .." or force deleting from there: https://kubernetes.io/docs/tasks/run-application/force-delete-stateful-set-pod/ it doesnt work. the pod is creating again and again...
The pods in a Statefulsets are managed by ReplicaSets and will be recreated again if the current and the desired replicas defined in the spec do not match.
The document you linked provides instructions as to how to kill the pods forcefully avoiding the graceful shutdown behaviour which can have unexpected behaviour depending on the application.
The link clearly states the pods will be recreated in the section:
Force deletions do not wait for confirmation from the kubelet that the Pod has been terminated. Irrespective of whether a force deletion is successful in killing a Pod, it will immediately free up the name from the apiserver. This would let the StatefulSet controller create a replacement Pod with that same identity; this can lead to the duplication of a still-running Pod, and if said Pod can still communicate with the other members of the StatefulSet, will violate the at most one semantics that StatefulSet is designed to guarantee.
If you want the pods to be stopped and new pods for the Statefulset do not get created, you need to scale down the Statefulset by changing the replicas to 0.
You can read the official docs for how to scale the Statefulset replicas.
The key to figuring out how to kill the pod will be to understand how it was created. For example, if the pod is part of a deployment with a declared replicas count as 1, Once you kill/ force kill, Kubernetes detects a mismatch between the desired state (the number of replicas defined in the deployment configuration) to the current state and will create a new pod to replace the one that was deleted - therefor in this example you will need to either scale the deployment to 0 or delete the deployment.
If we need to kill any pod we can just scale down the replica set.
kubectl scale deploy <deployment_name> --replicas=<expected_no_of_replicas>
Way of deleting pods will depends on how you created it. If you created it individually ( not part of a ReplicaSet/ReplicationController/Deployment ) then you can delete pod directly. otherwise the only option to delete is the scale option. In production setup what I believe is all are using Deployment option out of ReplicaSet/ReplicationController/Deployment( Please refer documents and understand the difference between all those three options )
Problem:
I want every pod created in my cluster to hold\point the same data
e.g. let's say I want all of them to have an env vars like "OWNER=MYNAME".
there are multiple users in my cluster and I don't want them to start changing their YAMLs and manually assign OWNER:MYNAME to env.
Is there a way to have all current/future pods to be assigned automatically with a predefined value or mount a configmap so that the same information will be available in every single pod?
can this be done on the cluster level? namespace level?
I want it to be transparent to the user, meaning a user would apply whatever pod to the cluster, and the info could be available to him without even asking.
Thanks, everyone!
Pod Preset might help you here to partially achieve what you need. Pod Preset resource allows injecting additional runtime requirements into a Pod at creation time. You use label selectors to specify the Pods to which a given PodPreset applies.
Check this to know how pod preset works.
First you need to enable pod preset in your cluster.
You can use Pod Preset to inject env variables or volumes in your pod.
You can also inject configmap in your pod.
Make use of some common label for all the pods which you want to have common config, use this common label in your pod preset resource.
Unfortunately there are plans to remove pod presets altogether in coming releases, but I guess you can still use it with current releases. Although there are other implementations similar to pod presets, which you can try.
I have a Kubernetes Deployment app with 3 replicas, which needs a 7GB storage for each replica, I want to be able to attach a new empty azureDisk storage to be mounted into each pod/replica created in this deployment.
Basically I have the following restrictions:
I must use Deployment, not a Statefulset
Each time a pod dies and a new pod is up, it shouldn't have a state, and it will have a new empty azureDisk attached to it.
the pods do not share their storage, each pod has its own 7GB storage.
the pods need to use azureDisk because I need a 7GB storage on demand, which means, dynamically creating azureStorage when I scale my deployment replicas.
When using azureDisk, I need to use it with Access mode type ReadWriteOnce (as says in the docs ) and it will attach the only 1 pod to this disk, that's found, but, that only works if I have 1 pod, if I have more than 1 pod, I can't use the same claim... is there any way to dynamically ask for more storages like the one in the first claim?
NOTE 1: I know there is a volumeClaimTemplates, but that's only related to a Statefulset.
NOTE 2: I don't care if a pod restarts 100 times, and this in turn creates 100 PV which only 1 is used, that is fine.
I'm not sure why you need to use a StatefulSet but the only I see to do this is to create your own operator for your application. The operator would have a controller that manages your pods similar to what a ReplicaSet does but with the exception that for every new pod that is instantiated a new PVC is created.
It might just be better to figure out how to run your application in a StatefulSet and use VolumeClaimTemplates
✌️
The main question is - Why? "if I have an application which doesn't have state, still I need a large volume for each pod"
Looking at this explanation you should focus on StateFull application. From my point of view it looks like you are forcing to use Deployment instead of StateFullSet for StateFull application
In your example probably you need pv which support different access modes.
The main problem you have experienced is that using pv with supported mode ReadWriteOnce you can bind at the same time only one pv by single node. So your pods in different nodes will not start due to failing volume mounting. You can use this approach only for ReadOnlyMany/ReadWriteMany scenario.
Please refer to other providers which have different capabilities for access modes like: filestore(gcp), AzureFile(azure), Glusterfs, NFS
Deployments vs. StatefulSets
What triggers init container to be run?
Will editing deployment descriptor (or updating it with helm), for example, changing the image tag, trigger the init container?
Will deleting the pod trigger the init container?
Will reducing replica set to null and then increasing it trigger the init container?
Is it possible to manually trigger init container?
What triggers init container to be run?
Basically initContainers are run every time a Pod, which has such containers in its definition, is created and reasons of creation of a Pod can be quite different. As you can read in official documentation init containers run before app containers in a Pod and they always run to completion. If a Pod’s init container fails, Kubernetes repeatedly restarts the Pod until the init container succeeds. So one of the things that trigger starting an initContainer is, among others, previous failed attempt of starting it.
Will editing deployment descriptor (or updating it with helm), for
example, changing the image tag, trigger the init container?
Yes, basically every change to Deployment definition that triggers creation/re-creation of Pods managed by it, also triggers their initContainers to be run. It doesn't matter if you manage it by helm or manually. Some slight changes like adding for example a new set of labels to your Deployment don't make it to re-create its Pods but changing the container image for sure causes the controller (Deployment, ReplicationController or ReplicaSet) to re-create its Pods.
Will deleting the pod trigger the init container?
No, deleting a Pod will not trigger the init container. If you delete a Pod which is not managed by any controller it will be simply gone and no automatic mechanism will care about re-creating it and running its initConainers. If you delete a Pod which is managed by a controller, let's say a replicaSet, it will detect that there are less Pods than declared in its yaml definition and it will try to create such missing Pod to match the desired/declared state. So I would like to highlight it again that it is not the deletion of the Pod that triggers its initContainers to be run, but Pod creation, no matter manual or managed by the controller such as replicaSet, which of course can be triggered by manual deletion of the Pod managed by such controller.
Will reducing replica set to null and then increasing it trigger the
init container?
Yes, because when you reduce the number of replicas to 0, you make the controller delete all Pods that fall under its management. When they are re-created, all their startup processes are repeated including running initContainers being part of such Pods.
Is it possible to manually trigger init container?
As #David Maze already stated in his comment The only way to run an init container is by creating a new pod, but both updating a deployment and deleting a deployment-managed pod should trigger that. I would say it depends what you mean by the term manually. If you ask whether this is possible to trigger somehow an initContainer without restarting / re-creating a Pod - no, it is not possible. Starting initContainers is tightly related with Pod creation or in other words with its startup process.
Btw. all what you're asking in your question is quite easy to test. You have a lot of working examples in kubernetes official docs that you can use for testing different scenarios and you can also create simple initContainer by yourself e.g. using busybox image which only task is to sleep for the required number of seconds. Here you have some useful links from different k8s docs sections related to initContainers:
Init Containers
Debug Init Containers
Configure Pod Initialization