How Do You Pass Two or More Subnets to an “aws eks” Command?

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Problem scenario
You want to pass more than one subnet to an “aws eks” command.

You tried to delimit the list with commas (or separate two subnet IDs with commas). You received this error message:

An error occurred (InvalidParameterException) when calling the CreateNodegroup operation: The subnet ID ‘subnet-0abcd1234,subnet-zyxw9876’ does not exist (Service: AmazonEC2; Status Code: 400; Error Code: InvalidSubnetID.NotFound; Request ID: Proxy: null)

What should you do?

…

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How Do You Get CentOS to Use the Internet Running Oracle VirtualBox (Because of an Error That the Network Is Unreachable)?

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Problem scenario
On a CentOS server running in VirtualBox, networking is not working. You cannot ping the default gateway or get to the internet. When you try to ping something, you get the error message in a terminal “connect network is unreachable.” What should you do?

Solution
In Oracle VirtualBox, go to Devices -> Network Settings. Make sure the adapter is attached to “Bridged Adapter”.

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What Happens Technically when Someone Opens a Web Browser and Goes to a Website?

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Question
Surfing the World Wide Web happens as a part of everyday life. In a job interview, you are asked to describe what happens behind the scenes when you open a web browser and enter a URL. The hiring manager wants to hear your knowledge of assembling packets of PHP, JavaScript, HTML, networking, or other technologies involved and how the sequence proceeds. What are the details of what happens behind-the-scenes?

…

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How Do You Attach a Lambda Function to a VPC?

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Problem scenario
When trying to attach a Lambda function to a VPC, you get an error like this: “The provided execution role does not have permissions to call CreateNetworkInterface on EC2”

What should you do?

Solution
1. Go to IAM and create a policy. Use the JSON editor. Use these settings (taken from StackOverflow):

{
“Version”: “2012-10-17”, …

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How Do You Handle a Discrepancy between NMAP Results?

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Problem scenario
From two different servers the nmap results show different ports are open. What is the likely cause of this problem?

Possible Solution #1
Is there a firewall between the two servers? Some firewalls block incoming or outgoing connections exclusively. An OS level firewall or other intermediate firewall could easily produce discrepant nmap results based on the servers running the nmap command.

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How Do You Connect to a VM in Oracle VirtualBox from a Desktop?

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Problem scenario
You are connecting to a VM in Oracle VirtualBox from a desktop. The pings to the VM are not responding. What should you do?

Solution
Go to Devices -Network -Network Settings
The “Attached to:” setting hould be “Bridged Adapter”
The “Name” setting should what you think is appropriate. Not uncommonly this will be en0 Wi-Fi.

…

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How Do You Troubleshoot “Some of the defined forwarded ports would collide” after Running a Chef Kitchen or Ansible Molecule Command?

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Problem scenario
You run a kitchen or molecule command. It fails with an error about ports. What should you do?

Solution
Find what other machines are running in your VPC. This error message seems to be relevant to Vagrant (because if you google it, you will see Vagrant-related postings). If you are using Vagrant, run this command: vagrant global-status

If you are not using Vagrant,

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How Do You Terminate a Process Listening on a Given TCP Port?

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Problem scenario
There is a process listening on a TCP port on your Linux system. How do you end it?

Solution
Assuming you want to terminate the process 5555, this is how you would find the PID:

sudo lsof -i :5555

To kill the process, the output of the above command will show you a PID. Run this command where 111222333 is the PID number you found above:

sudo kill -9 111222333 …

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How Do You Troubleshoot the Kubernetes Error “[ERROR Port-10250]: Port 10250 is in use”?

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Problem scenario
You are trying to run a kubeadm command. But you get this error:

[preflight] Running pre-flight checks
error execution phase preflight: [preflight] Some fatal errors occurred:
[ERROR Port-10250]: Port 10250 is in use
[preflight] If you know what you are doing, you can make a check non-fatal with –ignore-preflight-errors=…

What should you do?

Solution
Remove the kubelet that snap installed;

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How Do You Connect over Port 5986 on a Windows Server?

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Problem scenario
Port 5986 is blocked from your Linux server to your Windows server. You have used the nmap command and see that it is filtered. You believe there are no intermediate firewalls or OS firewalls blocking this port. What should you do?

Solution
This assumes you have no firewall blocking port 5986 for incoming connections to the Windows server. nmap will report 5986 is filtered despite there being nothing blocking this port if wsman’s listener has not been properly configured.*

  1. Run this script on the Windows server:

$hostName = $env:COMPUTERNAME
$serverCert = New-SelfSignedCertificate -CertStoreLocation Cert:\LocalMachine\My -DnsName $hostName
Export-Certificate -Cert $serverCert -FilePath c:\vagrant\PsRemoting-Cert1.cer
Get-ChildItem c:\vagrant\PsRemoting-Cert1.cer
Enable-PSRemoting -Force
New-Item -Path WSMan:\localhost\Listener\ -Transport HTTPS -Address * -CertificateThumbPrint $serverCert.Thumbprint -Force

  1. That is it.

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