A Technical I.T./DevOps Blog
Question
In computing, what is the definition of a schema?
Answer / schema disambiguation
Outside of the I.T. realm, Merriam-Webster’s Dictionary (11th Edition, on page 1110) defines schema as “a diagrammatic presentation; broadly: a structured framework or plan: outline.” This definition must have influenced the appropriation of the word to refer to concepts in I.T..
For Kubernetes
“Schemas are the set of JSON files for various Kubernetes versions,
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Problem scenario
You read that Kubernetes is ending support for Docker. What does this mean for Kubernetes users?
Solution
Probably nothing for most Kubernetes users. Kubernetes is going to support Open Container Initiative images.
Docker is more than a container runtime; its container runtime is containerd (according to twoardsdatascience.com). We expect containerd to be supported for a long time.
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Problem scenario
You are running Kubernetes in Azure. You need to find the Ingress pod’s IP address. What should you do?
Solution
1. Go to portal.azure.com
2. Go to Kubernetes Service
3. Go to the AKS cluster (e.g., foobar)
4. Go to Services and Ingresses
5. Find the ingress service with the name you are looking for (e.g.,
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Continue reading “How Do You Find the Ingress IP address for an AKS Cluster?”
Question
In the context of Kubernetes, what is a mutating webhook?
Answer
They are an API invocation that make changes to resources (and in some cases before they are created per medium.com).
“MutatingAdmissionWebhook is one of easiest ways of extending Kubernetes with new policy controls and resources mutation and a host of other options.” (Taken from medium.com )
“Mutating controllers may modify related objects to the requests they admit;
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Problem scenario
Your pods are not ready in Kubernetes. “kubectl describe pods” results may have errors like this:
Warning FailedCreatePodSandBox 4m57s (x2035 over 69m) kubelet (combined from similar events): Failed to create pod sandbox: rpc error: code = Unknown desc = failed to set up sandbox container “abcd1234” network for pod “apache-tomcat-deployment”: networkPlugin cni failed to set up pod “apache-tomcat-deployment” network: open /run/flannel/subnet.env: no such file or directory
(The symptoms of this problem will involve pods and nodes not being ready.
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Continue reading “How Do You Get Nodes in Kubernetes to Be Ready with a Network Plugin Error?”
Question
In the context of Kubernetes, what is a validation webhook?
Answer
They are an API invocation to confirm a resource was created properly. Unlike a mutating webhook, validation webhooks make no changes to resources deployed in Kubernetes. Also unlike a mutating webhook, validation webhooks happen at a different step in the admission controller process. The admission controller process starts with an API request and ends with persisting data to etcd.
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Problem scenario
You know that an admission controller in the API server has various stages to process a kubectl command in Kubernetes. You want to know how the API server or relevant admission controller works in the correct sequence. The sequence starts with a request (HTTP POST from a kubectl command) and ends with updating etcd. How does this happen in detail?
Solution
The API server’s process of handling a kubectl command is very similar to what are called “admission controller phases.”*
It is not clear what is the difference (if there is any).
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Problem scenario
You get a message “kubernetes cluster unreachable” when running a helm, kubectl, az, or eks command. What should you do?
Possible solution #1
Has a router been reconfigured? Has a new firewall rule been imposed? Has a data center gone down that housed the cluster? Did you receive an email about a maintenance window or a configuration change?
Possible solution #2
What are the permissions of the relevant .yaml file?
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Continue reading “How Do You Troubleshoot the Kubernetes Error “cluster unreachable”?”
Problem scenario
You do not have the YAML (.yml or .yaml) files for your Helm deployments.
How do you find the pod manifests for the yaml files when you do not have access to the Helm repos?
Solution
Run this:
helm ls -a -A
The output will show a “Name” on the left most column and a namespace in an inner column.
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Question
DaemonSets will bypass the scheduler and deploy to nodes that are designated as “unschedulable”; however you can use a DaemonSet to deploy to a subset of all the nodes (according to page 109 of Kubernetes in Action). In the real world, what are daemonsets used for in Kubernetes?
Answer
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Continue reading “What Are Common Use Cases of Daemonsets in Kubernetes?”