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Using kubectl patch to modify existing Kubernetes objects
2 min read
To be able to modify a Kubernetes object we can use kubectl edit to do it interactively. It can come handy if we need to test values but it makes it harder to automate it. If we need a way to change a Kubernetes object using a non-interactive command, kubectl patch is the best option for us.
18/08/2021
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Terraform: Using the external data source
2 min read
To be able to execute an arbitrary command to retrieve some data and being able to use it as a variable in terraform we can use the external data-source
17/08/2021
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Getting Kubernetes documentation using kubectl
3 min read
While forking on Kubernetes manifest it's easy to forget the available fields for each Kubernetes object. Using kubectl explain we can get all the fields available with a short description of them. Pretty much a man inside kubectl
13/08/2021
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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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