General


Upgrading Percona XtraDB Cluster

Guide can be found at https://www.percona.com/doc/percona-xtradb-cluster/5.7/howtos/upgrade_guide.html. 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 https://github.com/mysql/mysql-sys and […]


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: [bash]yum -y install firefox Xvfb libXfont Xorg[/bash] Then, install X-desktop: [bash]yum -y groupinstall "X Window System" "Desktop" "Fonts" "General Purpose […]


OpenVPN installation quick tutorial

Just a quick introduction for OpenVPN installation since there is a good work from https://github.com/Nyr/openvpn-install 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: [bash]wget https://git.io/vpn -O openvpn-install.sh && bash openvpn-install.sh[/bash] When installing, just remember to […]


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 myvpnserver.myserver.com, and server IP address is XXX.YYY.ZZZ.UUU . We […]


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, […]


Real IP from Amazon Load Balancers

If you are running an EC2 instance behind an Amazon Elastic Load Balancer (ELB), you’ll find that the visitors’ IPs are hided behind the load balancer, so your application cannot get the clients’ real IPs. In fact, visitors’ original IPs are passed via a X-Forwarded-For information in the header (http://docs.aws.amazon.com/ElasticLoadBalancing/latest/DeveloperGuide/x-forwarded-headers.html), […]