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Kubernetes Mutating Webhook: Patch a Kubernetes Pod on the fly - the hard way
6 min read
To be able to modify a request to the Kubernetes API server prior to persist the object (to, for example, inject a sidecar) we can use a Mutating Webhook. The admission controller makes a requests using all the MutatingWebhookConfiguration objects that matches the request and processes them in serial:
apiVersion: admissionregistration.k8s.io/v1 kind: MutatingWebhookConfiguration (...)Let's take a look on how to configure a mutating webhook from scratch
12/08/2021
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How to avoid pods of the same Deployment to be scheduled on the same node
2 min read
For some applications we might want to avoid having two or more Pods belonging to the same Deployment to be scheduled on different nodes, yet we don't need them to be a DaemonSet. Let's use as an example the cluster autoscaler: We would like to have two replicas but not on the same node, since if we are draining the node an there's not enough capacity on the other nodes with both Pods offline a manual intervention would be required to spawn a new node
$ kubectl get pods -n autoscaler -o wide NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES autoscaler-aws-cluster-autoscaler-585cc546dd-jc46d 1/1 Running 0 16h 10.103.195.47 ip-10-12-16-10.eu-west-1.compute.internal <none> <none> autoscaler-aws-cluster-autoscaler-585cc546dd-s4j2r 1/1 Running 0 16h 10.103.195.147 ip-10-12-16-10.eu-west-1.compute.internal <none> <none>To do so we will have to configure affinity
11/08/2021
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Loading a CSV file into terraform
2 min read
Sometimes if you have some externally managed data it can come handy to be able to import it into terraform as a CSV file instead of having to manually enter all the date. To do so we can use the csvdecode() function
10/08/2021
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What's a Kubernetes Deployment object?
2 min read
Maybe the most common object used for deploying applications on Kubernetes is the Deployment object. It is intended to provide declarative updates for Pods at a controlled rate.
With a Deployment we are setting the desired state of a ReplicaSet. The Deployment controller will take the appropriate actions to adjust the ReplicaSet so it has the correct amount of Pods
09/08/2021
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What's a Kubernetes Job?
2 min read
A Kubernetes Job is an object that contains a Pod definition, just as a Deployment do, but instead of expecting the Pod to be continuously running, it is expecting it to finish. In case the Pod execution fails, it will continue to retry execution until a specified number of them successfully terminate.
05/08/2021
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Kubernetes startupProbe: testing containers for application startup
2 min read
Starting from Kubernetes v1.20 we can configure a startup Probe: It will check for containers to be come into service, disabling liveness and readiness checks until it succeeds.
05/08/2021
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Kubernetes deployment strategies
2 min read
To update a Deployment objects we can choose between two built-in strategies used to replace old Pods by new ones: Recreate and RollingUpdate
Let's see the differences between them
04/08/2021
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Kubernetes: What's a PodDisruptionBudget?
2 min read
In Kubernetes we can configure a PodDisruptionBudgets (PDB) to tell the cluster for a given set of Pods how they can tolerate interruptions (such as application upgrades) maintaining it's general availability.
This Kubernetes object has graduated to GA in Kubernetes v1.21
03/08/2021
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Kubernetes: cannot delete Pods with local storage
2 min read
While draining a node it might fail with the message cannot delete Pods with local storage as follows:
$ kubectl drain tycho.pet2cattle.com --ignore-daemonsets node/tycho.pet2cattle.com already cordoned error: unable to drain node "tycho.pet2cattle.com", aborting command... There are pending nodes to be drained: tycho.pet2cattle.com error: cannot delete Pods with local storage (use --delete-emptydir-data to override): spinnaker-ampa/spin-rosco-658fdb4694-v99jt02/08/2021
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