Sometimes, especially during work in lab environments we need to stop all our instances ie. to avoid additional charges from cloud operator. Openstack offers a convenient way to do it – shelving. When you shelve an instance all machine’s volumes are saved but VM instance does not utilizing compute host resources. This state persists until you unshelve a specified machine. Openstack does not offer option to shelve/unshelve of all your instances at once, you need to do it on every machine separately. This simple bash script gives you an ability to shelve or unshelve all machines at once. Continue Reading

Sometimes (especially when system works on heavy load) Linux buffers and caches contains a lot of objects. This behaviour is generally highly desirable but let’s take a look at following scenario.

Web server is a victim of a DDoS attack. Most of free RAM is used by caches. DDoS has ended and we quickly need to free some RAM for our main application and database system. Cache will warm-up again but it take some time. We need to initiate cache warm-up now! Continue Reading

Default CentOS repositories contain only most popular packages and doesn’t offer useful packages that are available in other Linux distributions. EPEL repository is an Extra Packages for Enterprise Linux. It provides rebuild of Enterprise Linux packages of Fedora for EL6 and EL7. Generally using that repository is safe and significantly improves system functionality. How to install it? Continue Reading