Inventor's Paradox

The freezing app problem When dealing with a freezing application, most management (or even management with IT background) will say it is related to capacity problem. Usually the capacity are correlated to how many processor core, how many gigabytes memory available to the system, and how much bandwidth are available. The reality is not that simple.  When an application freeze or slows down, it is to the best interest of the application team, whether operational, development, devops team, or service team (as it is said in the ITIL), to find out how to make it accessible again, and in management terms, increase the system's capacity. The first step to do that, is to actually determine the bottleneck, which traditionally is done by checking memory usage, CPU usage, and network link usage. But I am not thinking to make this a traditional post, so in this post I will try to describe other stuffs that could cause slowdown or freezing app problem. The APM way of things Today we have APM ...

Background The default behavior of Openshift nodes is to redirect requests for unknown applications to host/getting_started.html, usually causing endless redirect loop. On some cases we might want this behavior to be changed, for example when we want a default page (Application not found) to show up. Or when tools such as Acunetix scanning tool incorrectly detected such redirect as medium vulnerability because the redirect uses the injected host header. The Openshift Origin platform in use for this article is Origin Release 4, with the nodes using apache-mod-rewrite frontent plugin (rubygem-openshift-origin-frontend-apache-mod-rewrite-0.7.1.1-1.el6.noarch).  Mechanism The default mechanism can be read in /etc/httpd/conf.d/000001_openshift_origin_node.conf : As we can see, routes are loaded from openshift_route.include.  The file is full of route rules, but the interesting part are the RewriteMap clauses in the top of the file : Nodes and aliases are...

The Joget Workflow Engine have JSON API interface which could be used to query and control workflow processes. This will be useful if we need to implement a custom front-end UI for joget workflow. Especially if the development team have minimum or even zero Java development experience. I have created two API test applications, one is using PHP and the other is written in C# using .NET framework. The PHP version is written using the wonderful Yii Framework. The C# version is a windows forms application, but the WorkflowService class theoretically could be used in ASP.NET application. Feel free to download and try ... jogettestnet (C# .NET Windows Forms App) jogettestphp (Yii-based PHP App) To start using this test application, you must first configure joget to allow login using master login username and master password (click System Settings:General Setting, find the section System Administration Settings). Fill the master login & password (in my example, superuser and ...

This post is dedicated to accidents that every so often resulting in deleted rows of data. Of course everyone should have backups. But things do happen when the backups nowhere to be found, or not being done often enough, or we're storing data in a forgotten database server. In the event of such incident.. deactivate your apps. Prevent unnecessary writes to db that could make your data overwritten. In case of oracle database, you could try flashback query that assume the transaction is still fresh in the redo log. In case of mysql database, copy the whole data directory into a safe location, where we would try to dump deleted rows using Percona Innodb recovery tool. But such methods failed miserably when we found out about the accident much too late. I think every person should be responsible for their actions, even if the action is about deleting data. But the consequence of mass-delete actions is very different from single-row deletes. That is why mass delete function must be ...

Have you ever deployed an application, and  find out that its real world performance is less than what you expect? Maybe you haven't got time to do proper load testing, or maybe the production environment have different performance characteristic. Fear not because for some common issues we could still improve performance even when time running out. In this blog post I will try to create conceptual framework for troubleshooting enterprise application performance. Enterprise application in this context is actually synonymous to information system (as Martin Fowler has said in his Patterns in Enterprise Application Architecture). I will use three application that I have engineered as examples. The first, application P, is primarily used for viewing the result of complex business logic calculation, have transactional features but the transactional function usage is 1 : 10 to the view/report function. The second, application C, is primarily used in transactions. The third, applicatio...