DEV Community: aquila

CKA 2020 September

aquila — Mon, 28 Sep 2020 12:23:17 +0000

I took CKA exam in this September and passed it. So let me share my experience and thought on it.

CKA, Certified Kubernetes Administrator, is mainly provided by Linux foundation.
https://www.cncf.io/certification/cka/

It's updated this September, so check what's changed.
https://training.linuxfoundation.org/cka-program-changes-2020/

Here's some points to know...

Exam duration is 2 hours
17~20 questions
Each question has 4~13% weight
Passing line is 66%
Only official docs can be refered during the exam https://kubernetes.io/docs/home/ (and k8s github page?)
Be sure that your desk/working space is cleared. Nothing on the wall, under your desk
No smartwatch on your wrist
Test result will be sent out within 36 hours after test completion. In my case, I waited for 34 hours.

Preparation is key
I used 2 website to get ready for the exam.

1/ Udemy, CKA course
https://www.udemy.com/course/certified-kubernetes-administrator-with-practice-tests/

This is very popular among CKA candidates. It covers 90% of exam topic(as of now), and starts from very basic.
But, may be because of september updates, some topics are not covered(StatefulSets, Service account for example). For those, you have to take CKAD course.

2/ Killer.sh
https://killer.sh/

No lecture part, only practice tests (and detailed answers). Comparing to udemy course, this is much harder. It is targeted to "hard" level of actual exam. So it is a good reharsal.

Some thoughts

I don't think you need to use tmux. In my opinion, it doesn't help much. If you are not used to it, learning cost is a bit high, and it doesn't pay off much.
alias, export and auto completion of kubectl is your friends. Some people says auto completion is too heavy to use in exam environment, but it was no problem for me.

Let me know if you have any question, I'll answer that as possible!

Install terraform on ubuntu

aquila — Sat, 11 Apr 2020 09:17:52 +0000

OS info

vagrant@ubuntu-xenial:~/downloads$ cat /etc/release
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=16.04
DISTRIB_CODENAME=xenial
DISTRIB_DESCRIPTION="Ubuntu 16.04.6 LTS"
VERSION="16.04.6 LTS (Xenial Xerus)"

Download zip file
wget https://releases.hashicorp.com/terraform/0.12.24/terraform_0.12.24_linux_amd64.zip

Unzip it
unzip terraform_0.12.24_linux_amd64.zip

Export PATH
export PATH="$PATH:<Path to terraform unzip file>"

Reflect new path
source ~/.profile

Test
terraform --version

JConsole connects to Guest OS

aquila — Tue, 24 Dec 2019 07:06:13 +0000

What I want to do: Using JConsole, monitor java application which running on guest OS.

First attempt
I couldn't connect to guest os, so I learnt how to configure the network between Guest OS and Host OS

Guest OS configuration
I'm using Vagrant to manage VMs(Virtual box) on my windows. Basically what I need to do is to configure Host-only adapter. Default adapter is NAT. This is mandatory. So we cannot change it to Host-only, instead, we need to add another adapter which is Host-only.

This can be achieved by adding 1 line in Vagrantfile.
config.vm.network "private_network", type: "dhcp"
or
config.vm.network "private_network", ip: "192.168.33.10"

Then you can see that a new adapter is added by "ip a". You can try pinging to the ip. In below example, it is 172.28.128.3.

Java option
To be visible from Jconsile, you need 2 options.
-Dcom.sun.management.jmxremote.port=PORT
-Djava.rmi.server.hostname=IPADDRESS

Connect as remote
You can connect to IPADDRESS:PORT in jconsole start screen.

Vagrant commands

aquila — Sun, 22 Dec 2019 09:07:10 +0000

Vagrant commands which often use

1/ Initialization
vagrant init

2/ Start&Stop
vagrant up
vagrant halt

3/ Remove vm
vagrant box list (you can see the NAME of envs)
vagrant box remove NAME

4/ Remove whole config file
vagrant global-status (to list env ids)
vagrant destroy [name|id]

5/ Export VM box
vagrant package

6/ Open VM box
vagrant init
vagrant up

Capture ping on linux using Wireshark

aquila — Mon, 25 Nov 2019 06:39:23 +0000

On linux, I want to capture ping incoming/outgoing.
Then I installed wireshark with yum command.
yum install wireshark

To watch ping,
tshark -2 -R icmp

"-R" is the option to filter on read, it must be used with -2.
icmp is protocol which is used by ping

JVM tmpdir option

aquila — Tue, 22 Oct 2019 09:13:38 +0000

By default, JVM creates tmp dir under /tmp/
This setting can be changed by adding JVM option
"-Djava.io.tmpdir=mytmpdir"

1 tricky thing is mytmpdir should be exist before starting Java process.

So steps should be
1/ add JVM option -Djava.io.tmpdir
2/ mkdir mytmpdir
3/ restart java process