I am trying to create a custom kubernetes controller which keeps the track of the number kubernetes resources, for example count the number services created in a cluster.
there are 2 parts to the above question:
1st I need to create a controller which listens to when a service is created, lets call this counter as svc_count. This is easy, as I can write a custom controller to listen on services.
I need to store the svc_count in the etcd, so that I can show the value
when some user queries for the svc_count. So I thought of using the CRD's. I can do that by following the example in https://github.com/yaronha/kube-crd. This has the Rest-API-client to POST,PUT,GET.
The 3rd part is relating the part 1 and part 2. Whenever a Service is created, then in the ADD eventhandler of the controller I need make changes to the CRD, so that the user can see the update.
Issue/Question: My question how to update a CRD from the custom controller's eventhandler??. Can I save the CRD rest-api-client in the custom controller and call the respective Update function.
Please, let me know if there is any other way of doing this.
Thanks
Related
I am trying to find a way? If I create a new namespace then I want it to create a RBAC rule for that serviceaccount automatically.
I know one way is to create an operator so, that there is an event that is traced by reconciler / api server and it creates the resources based on CRD's. Is there any other way?
While not really intended for this kind of thing you could use admission controllers (https://kubernetes.io/docs/reference/access-authn-authz/admission-controllers/) to achieve something like that.
Due to it's nature the admission controller is called before the namespace exists and you would need to wait until its creation is finished to create objects within that namespace. For that the admission controller call needs to be completed, else the namespace can't be created. I.e. by calling a second service that waits until the namespace is actually created.
I asked a similar question here: Automatically create Kubernetes resources after namespace creation (I didn’t find yours at that time).
I ended up writing a controller that does exactly what you need: https://github.com/blakelead/nsinjector
In short, you deploy a custom resource specifying resources to deploy and patterns for namespace names you want to target.
I have two Rest data sources, with their respective proxy-service.
But can I create one service that calls the right proxy-service instead of doing it directly on the controller? Is that possible?
Thank you so much
At the end, yes it is.
Just create a new service with this option:
enter image description here
And then inject the proxy-services you need. On this way you can delegate some logic from controller to this service.
I have created a custom resource definition (CRD) and a custom resource (CR) in my Kubernetes cluster, but in my CR controller, how do I create Kubernetes events which are attached to my custom resource? I hope with events, users will be able to see important messages associated with the CR when they run kubectl describe <cr>.
You're looking for an operator. There are already a few pre-written ones out there, check OperatorHub. They are essentially controllers for custom resources, watching for events and acting on them.
You can also write your own, e.g. with the Operator SDK. When you write your own, you can update the status of the CR, depending on what your operator should do, which then shows up when calling kubectl describe.
A good start might be this post on Operators, and this here for listening to events from your custom resources.
Description
I have a CR associated with a POD with a container that is exposing an API, eg:
/available
returning for example
{"available":"true"}
Is there a way to create a controller watcher on that API call that whenever the response changes will trigger the reconcile function?
I believe it could be possible using a channel with the controller watcher, but I don't see any similar examples out there
Using
Kubernetes operator-sdk version v0.5.0+git
I'm afraid it's not as easy as you hope. The Kubernetes controller objects react to add/edit/delete operations of some kind of resource in the cluster. A value exposed inside an API of something running inside the Pod is not visible in the resource database. There is not event going off, notifying about the change either.
I see two things you can consider doing:
Create a regular controller that would have the reconcile function triggered fairly often, but would check the availability value inside it's reconcile function. If it changed, it would do something, if it didn't it would do nothing.
Just create a separate task, outside the controller domain, that would monitor this API value and do something.
Controllers work using notifications, they don't actively watch for changes, they are notified about them. That's different than what you want to do - periodically check the API response.
I'm trying to get my head around mvvm and came up with a test application that I think will give me a good foundation. Suppose my application has a service that goes out every minute and gets the latest flight arrival and departure information at an airport. Now suppose I have 3 different views: InboundView, OutboundView and GateView. The Inbound and Outbound views would simply display the various flight details for inbound and outbound flights that I'm sure we've all seen on the flight boards in the airport. The GateView would display similar flight information but might be sorted by gate # instead of flight #.
So the model for the Flight object would contain the flight data details as well as an instance of a Gate object that would be updated appropriately once a flight arrives.
So all 3 views are using the same flight data service and I know I can pass an instance of that service to each VM but then I'd need to hook up the appropriate INPC events at each view model and that seems less than ideal as the number of views/vms increases.
Right now, each VM uses a ListCollectionView wrapped around the passed in collection of flight data and I just sort/filter based on inbound/outbound, etc.. but I was hoping to incorporate the service results into a sort of parent view model that would then pass a reference to itself along to the sub-views and then I could just handle all the INPC, etc.. events at the parent view model level and those will automatically trickle down to each of the subviews if data on a particular flight changes (such as its gate) instead of having to handle that separately in each of the VMs.
I've looked into the Messenger framework for MVVM Light but it still seems like each of the sub-VMs would have to register for the message and respond to it individually.
Does that make sense? Am I on the right track here?
So all 3 views are using the same flight data service and I know I can pass an instance of that service to each VM but then I'd need to hook up the appropriate INPC events at each view model and that seems less than ideal as the number of views/vms increases.
You don't necessarily have to do this, if the "service" implements INotifyPropertyChanged. Remember, you can bind to a property within a property, ie: {Binding Path=FlightService.Gate} or whatever, which may work. (It's difficult to know your requirements here, though.)
I've looked into the Messenger framework for MVVM Light but it still seems like each of the sub-VMs would have to register for the message and respond to it individually.
Yes, if you wanted to use a messaging framework, you would need this to be handled in each of the ViewModels. Alternatively, you could use some form of service location or constructor injection to "pull in" the flight service. The latter is my personal preference here.
The advantage of handling this in each VM is that each VM will likely want to handle things somewhat differently (otherwise, why is there more than 1?). By pulling a reference to the service in via IoC, you can handle this anyway you need to.