POSIX compliant filesystems

Posted on May 3, 2021June 28, 2021 by Marco Antonio Carcano

Don’t be tempted to skip this post: you would miss something valuable. Of course most of us know how to operate a filesystem, but the underlying details of POSIX filesystems are not broadly known by most of the people. In this post I describe them quite accurately, trying to keep at a level that may intrigue, but avoiding to be too theoretical. Having such an expertise is certainly one of the things that make the difference from a technician and a skilled professional. In addition to that, this skill may really save your life when facing weird things that sometimes may arise.

SPC-3 Persistent Reservations and Fencing

Posted on April 13, 2021May 15, 2021 by Marco Antonio Carcano

Clustered file systems are powerful but they should be carefully implemented to avoid split brains, since it is very likely that these lead to data corruption. A very effective way to cope with this risk is SCSI fencing: this trick denies access to the shared disks from nodes that are considered failed by the majority of the nodes of the cluster. The only requisite to implement SCSI fencing is that the shared storage should support SPC-3 Persistent Reservations. This post talks about this topic and explains how to configure a stonith device that exploits SCSI fencing.

JSON Web Token – JWT

Posted on April 13, 2021June 15, 2021 by Marco Antonio Carcano

JWT provides a convenient and standard way to securely transport claims from an issuer to its audience over HTTP. It can be used for authentication and authorization purposes, as well as non repudiable information exchange. It's easiness of setup along with the pros of being transportable over a simple and plain-text protocol such as HTTP and of being stateless (session data can simply be put inside the claims) made it be broadly adopted by developers, whenever it does not worth to implement more cumbersome frameworks such as OpenID or OAuth. In this post we explore JWT and its related standards JWS and JWE.

Designing infrastructures – defining corporate’s standard tiers

Posted on April 13, 2021May 15, 2021 by Marco Antonio Carcano

Infrastructures are the foundations used to provide services: since services are subjected to confidentiality and availability requirements, infrastructures must be designed so to provide several confidentiality and availability tiers. This way a service can be placed on the part of the infrastructure that meets the availability and confidentiality requirements for its use case. This means that one of the very first things to do when designing infrastructures is defining the corporate's standard tiers.

Vagrant – Installing and operating

Posted on April 12, 2021September 23, 2022 by Marco Antonio Carcano

Vagrant is a personal tool to automatically provision virtual machine environments. It comes for free along with VirtualBox plugin, although there are commercial plugins for other virtualization engines such as VMWare. It is a very handy tool, especially for developers: it enables them to quickly mock-up or destroy even complex virtual machine environments by executing just one command. Within this post we'll see how easily it can be installed, and how easy it is operating with it.

Memory Management – The Buddy Allocator

Posted on April 9, 2021October 6, 2022 by Marco Antonio Carcano

Every skilled professional should have an understanding of how the kernel does allocate memory: sooner or later it happens to get a system stuck complaining that it cannot allocate memory, despite the output of the "free" command showing that there's plenty of memory. This can get people confused, however this only means that the system cannot allocate kernel memory, despite it can still allocate system memory. The aim of this post is to clarify how the kernel allocates physical memory using the buddy algorithm, along with the available tools to check the state of physical memory.