Validate a Let’s encrypt certificates on CloudFlare-enabled websites

In this quick tutorials, I will mention a method to Auto-Renew / Validate a Let’s encrypt certificates on CloudFlare-enabled websites. As you may know, if you use CloudFlare for DNS/CDN purposes, then you cannot access to several server ports for Let’s Encrypt to validate the certification request. So in this […]

Upgrading Percona XtraDB Cluster

Guide can be found at There is no need to re-invent the wheel. I am too lazy to do it. Issue 1: If you are running mysql_upgrade and face the following error: “mysql_upgrade: [ERROR] 1136: Column count doesn’t match value count at row 1”, just do as follows: Clone and […]

Setting up ReactJS Development environment with Babel and WebPack

This quick guide is to help you setup ReactJS Development environment with Babel and WebPack. The post is mostly copied from Source: I post it here for later personal reference. Let’s start from scratch Create a new folder ‘react-hello-world’ and initialize it with npm. Accept the default for all the […]

Running Selenium with FireFox browser in CentOS

Quick note here the necessary steps to install and run Selenium with FireFox browser in CentOS. We will need to setup XWindows for Headless Selenium with FireFox webdriver. First, install Xvfb: Then, install X-desktop: Next, launch a XWindows Virtual Frame Buffer (XVFB) session on display port 99: In the same terminal session, export […]

Install Jenkins for PHP Continuous Integration

Today I will mention how to install Jenkins and necessary plugins/tools for doing Continuous Integration. This is just a very first step of using Jenkins for PHP Continuous Integration work. I choose to start with a Virtual Machine with Ubuntu 16 and use LAMP with PHP7 for the web stack. […]

OpenVPN installation quick tutorial

Just a quick introduction for OpenVPN installation since there is a good work from that helps install in 1-click. I just add some extra notes when installing as well as connecting for future references. First, run the one-step installation command: When installing, just remember to choose “1) Current system resolvers” for the […]

Install OpenVPN server CentOS 7

Today I will brief necessary steps for installing OpenVPN server CentOS 7. This will include custom server name and also rules for csf firewall which is widely used. The OpenVPN server name in this tutorial will be myvpnserver, associated domain will be, and server IP address is XXX.YYY.ZZZ.UUU . We […]

Install Chef server Lets Encrypt

Do not want to mention what Chef is, or what Let’s Encrypt is. This is just a short step-by-step tutorial to guide you how to install Chef server Lets Encrypt for the server SSL. Setup Let’s Encrypt First, install let’s encrypt to generate a standalone certificate before installing chef server: […]

Migrate Gitlab to new server

When migrating gitlab to a new server, you might face much problems of in-compatible versions, different OS (so different latest gitlab version), etc. The best way is to upgrade the old server to the same latest gitlab version, then backup gitlab, and then transfer the backup to the new server, […]

Connect to Amazon Cloud Drive from Debian Command line

We are going to connect to Amazon Cloud Drive from Debian Command line to utilize the benefit of unlimited cloud storage. Even there are various tutorials out there, finding a really “workable” one is not a trivial work. I summarize some steps here for reference. First, we need to install […]