What Do You Need to Do to Get a RHEL Server to Be a DNS Server?

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Problem scenario
You have a RHEL server in AWS.  You want it to be a DNS server.  What do you do?

Solution
For security reasons, you should have the network that this DNS server will serve be behind a firewall.  Following a short Question and Answer guide like this is fine for testing and learning.  However, denial of service attacks are more possible when a primary DNS server engages in recursive look ups (page 857 of A Practical Guide to Fedora and RedHat Enterprise Linux).

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How Do You Access the SonarQube Web UI When It Is Only Listening on the 127.0.0.1 IP Address?

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Problem scenario
SonarQube is listening on the loopback IP address on port 9000.  SonarQube is not listening on the external IP address.   You want to access the web UI for SonarQube. What should you do?

Solution
Install a web server and configure it to connect to port 9000.  Here are the details for using Apache web server on a Red Hat derivative (e.g., CentOS/RHEL/Fedora).

1. 

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What Is The Difference between a Kubernetes Service, the Kubelet, and the Kubernetes API?

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Question
You know of different Kubernetes components: the Kubernetes Service, the Kubelet, and the Kubernetes API.  What do these components do and how are they different?

Answer
A Kubernetes service is an entity, that may span nodes, that keeps a group of Pods functional and coherent (paraphrased from this site).  A “[s]ervice will get its own IP address and port” as quoted from page 339 of Kubernetes in Action. 

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How Do You Trace the Route of a Network Path from One Server to an IP address elsewhere on the Network?

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Problem scenario
You want to see the path that network traffic takes from one server to another network endpoint.  How do you find the intermediate path from the server your are on to a reachable IP address?

Solution
Use a tracing utility.  If your server is running Windows, use tracert.  Here is an example of how to use it:  tracert 8.8.8.8

If your server is running Linux,

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How Do You Log onto a Free WiFi Network When There Is a “Internet not available” Error?

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Problem scenario
You try connect via your wireless router to a WiFi network (e.g., at a restaurant, hotel, or public library).  You open a web browser because you were told you would be prompted with a splash screen.  On this page you would agree to the terms of service and/or enter a password.  You are not seeing this web page.  You try different URLs (e.g., www.yahoo.com, www.google.com).  You are never prompted for a username or password.

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How Do You Access the Networking Port of a Docker Container When There Appears to Be No Port Mapping, Just a Single Port Exposed by Itself?

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Problem scenario
You run “docker ps -a” and see values in the PORTS column.  You see values such as these for two separate containers:

Container 1 has this:  0.0.0.0:32775->5000/tcp

Container 2 has this:  5731/tcp

You cannot reach the containers that have no “->” symbol in them via web browsers or other network connectivity tools.  You can reach those containers with the “->” symbol in the PORTS value. 

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You Cannot Connect To One IP-Enabled Device to Your WiFi Router Wirelessly. What Do You Do?

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Problem scenario
You can connect the device with a network cable (in a wired fashion) to your network including the WiFi router’s physical ports.  The wired connection works.  You can connect other devices to the WiFi router wirelessly.  You can even connect  the IP-enabled device with the problem to other wireless routers.  What is wrong?

Possible Solution #1
See if the incompatibility comes from the WiFi router having an access control list enabled. 

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How Do You Remotely Connect with a GUI Interface into a Raspberry Pi 3 from a Windows Computer That Is on the Same Network?

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Problem scenario
You want to connect to your Raspberry Pi 3 with a Windows machine (e.g., Windows 7 or Windows 10 laptop).  Both are on the same network.  You want more than the command line interface.  You want a desktop GUI connection beyond just a character prompt.  What do you do?

Solution
On the Raspberry Pi do these three steps:
1. 

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How Do You Enable IP Version 4 Forwarding on an Ubuntu Server?

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Problem scenario
You want to enable IP version 4 forwarding on an Ubuntu server permanently.  How do you do this without rebooting?

Solution
1.  Run this command:sudo sysctl -w net.ipv4.ip_forward=1

2.  Modify the /etc/sysctl.conf file. Use “sudo vi /etc/sysctl.conf“

Uncomment out this stanza:

net.ipv4.ip_forward=1

3.  Save the changes. 

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How Do You Delete an AWS Security Group When You Get a Message about It Being Attached to a Network Interface?

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Problem scenario
Recently you deployed Kubernetes to AWS using JuJu.  You are now eliminating the Security Groups that it created. You cannot delete a Security Group in AWS.  You get an error about the Security Group being associated with one or more network interfaces.   You cannot detach the network interface.  You even click the “Force detachment” and then click “Yes, Detach.”  Nothing works to delete the network interface or remove the Security Group.

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