What Is The Watch Mechanism in Kubernetes?

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Question
What is the “watch mechanism” in Kubernetes?

Solution
A notification system from the API server to trigger changes in Kubernetes. In Kubernetes there are observable events. The watch mechanism is a system for listening for specific events to respond to. The Kubelet, the Scheduler, the kube-dns pod, and individual controllers are components that use the watch mechanism. The API server is a central component that watching components are aware of.

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How Do You Troubleshoot the pipenv error message “tomlkit.exception”?

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Problem scenario
You try to run a pipenv command, but you get an error about “tomlkit.exception”.

Solution
Copy the Pipfile to a new name (to back it up). Delete the original Pipfile. Try to run the command again. If it still fails, try removing pipenv by uninstalling it. Then reinstall pipenv. Then reboot the computer.

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How Do You Install and Configure Apache Camel on a Linux Server?

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Problem scenario
You want to install and configure Apache Camel from source on any distribution of Linux. What do you do?

Solution
You cannot. But there is a way to use Apache Camel as a test.

Background: It is not something that is can be purely installed-and-configured like other applications. Camel is a framework for integrating messaging solutions or microservice architecture.

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How Do You Troubleshoot an Error about sqlite3 Not Being Installed when It Is Actually Installed?

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Problem scenario
You have installed sqlite3. It is a version above 3.22.0. But when you run “make deps” you see this error message:

checking for SQLITE… no
configure: error: Package requirements (sqlite3 = 3.22.0) were not met:
No package ‘sqlite3’ found

What should you do?

Solution
Run this:
sudo apt -y install libsqlite3-dev

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How Do You Get the NameNode Process to Start in Hadoop?

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Problem scenario
You have run start-dfs.sh and start-yarn.sh. You have stopped all the Hadoop services too. When you run “jps”, the NameNode is not showing up. You have tried a variety of different troubleshooting methods (including rebooting the NameNode). The NameNode has never worked correctly. You can delete all the data in the cluster because it never really worked. What should you do?

Solution
Run this but remember it will delete all your data:

hdfs namenode -format # Warning: this command will delete all your data in Hadoop …

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How Do You Troubleshoot the fdisk Error “cannot open /dev/sdaX: No such file or directory”?

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Problem scenario
You have added a partition to Linux. When you type “df -h” you do not see evidence that it is available. You tried the “sudo lsblk” command, but you do not see the device. The “fdisk -l” command does show the new device and the size that is available. The command ll /dev/sd* does not show your new device.

When you run “fdisk /dev/sdaX”,

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How Do You Use an Array in Linux (Bash)?

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Problem scenario
You are aware that arrays are a supported data type in Bash. You would like to iterate through some variables as arrays could enable complex logic. What do you do?

Solution
The array is zero-based. So the first element is referred to by index number 0.

continualarray=(dog cat hamster rabbit horse cow)
echo ${continualarray[2]}
echo ${continualarray[5]}

Create a file foobar.txt to test an array’s line-reading capacity.

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How Do You Create a Windows 2016 Server with Vagrant and Oracle VirtualBox?

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Problem scenario
You want to use Windows 2016 with 2 GB of RAM. You have Oracle VirtualBox installed on a Linux server. You want the VM to be able to communicate with the host or other VMs on the host. You have a license for Windows 2016. What should you do?

Solution
Prerequisite: You have Oracle VirtualBox set up. You know what adapters you can attach a VM to.

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How Do You Write a Java Program to Accept a Character as Input and Do Something with It?

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Problem scenario
You want to accept user input with a Java program. How do you write such a program?

Solution
Here is the program:

import java.util.Scanner;

public class acceptChar {

public static void main(String[] args) {
System.out.println(“Please enter a character, then press enter: “);
Scanner in = new Scanner(System.in);
char letter = in.next().charAt(0);
System.out.println(letter);
}
}

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