Crouching Supervisor, Hidden File Descriptor Setting

Here’s an interesting problem our team faced last month that was extremely infuriating. We were in the process of launching replacement haproxy instances that are used to load balance to nodes in our RabbitMQ cluster. We’ve done this a lot of times before and set all the usual user settings required under limits.d to ensure proper file descriptors are allocated ...

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Managing Dotfiles With Ansible

Yesterday I posted about managing our local configuration with Ansible and today I’m going to continue this path by putting my zsh configuration under configuration management. Installing ZSH and oh-my-zsh First up let’s install our preferred shell and customizations. For me this is zsh and oh-my-zsh. Up front I know that this is going to probably be a multi-step process ...

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Virtualization with VirtualBox: Installation and Configuration

This article is part of our Academy Course titled VirtualBox Tutorial: Virtualization Essentials. In this course, we provide a compilation of VirtualBox tutorials that will help you get started with this virtualization platform. We cover a wide range of topics, from installing the software and performing a basic configuration, to cloning, exporting, importing, and removing virtual machines. With our straightforward ...

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Storing X.509 Digital Certificates (And Other Messy Things)

We often need to store structured binary data in our database – images, pdf documents, etc., but also have a need to search by, or index on, attributes of that data. E.g., we might store the height and width of an image, or the OCR text from a PDF document (for full text searches). The normal solution is to store ...

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Linux cut Examples

Cut is a Unix command line utility which is used to extract sections from each line of input, usually from a file. It is currently part of the GNU coreutils package and the BSD Base System. It first appeared in AT&T System III UNIX in 1982. Extraction of line segments can typically be done by bytes (-b), characters (-c), or ...

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Apache HTTP Server Tutorial

Course Overview The Apache HTTP Server, colloquially called Apache, is the world’s most used web server software. Originally based on the NCSA HTTPd server, development of Apache began in early 1995 after work on the NCSA code stalled. Apache played a key role in the initial growth of the World Wide Web, quickly overtaking NCSA HTTPd as the dominant HTTP ...

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Database Threat Models

I finally have a breather and can start working through my backlog of ideas. I start with some background that will make the motivation for subsequent posts clearer. What are the threat models for the persistence layer of an application, specificially the threats against the database itself? Remember that a ‘threat’ is an adverse act, whether intentional (by an attacker) ...

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Dense Virtualization via Linux Containers

We are living the era of buzzwords, and Docker is for sure one of those in the technological landscape. Docker has a common sense definition: hypervisor-free virtualization. In other terms: running VMs without any hypervisor-based virtualization support. Now, how is this possible? What is the arcane trick to achieving that? Let’s live a short journey to sketch the context out, ...

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