Karlsen Info Systems

[ Consulting ]

I'm available for one–off or longer-term consulting in a variety of technologies, ranging from user-layer applications all the way down to the physical network layer.

My areas of expertise include typical internet–based services like web, mail, file transfers, and other communication protocols.

I am often pulled in to solve challenges where the usual out–of–the–box methods fail to produce the desired result.

Internet–based services

  • Web
  • Email
  • DNS
  • Routing and firewalls
  • VPNs

Internetworking

I have been running public–facing services on the internet for many years.

This includes web servers, mail servers with and without webmail, file servers, both authoritative DNS servers and resolvers, and many other services.

Storage and backup

I recommend using ZFS wherever possible. Its features and reliability put it miles ahead of anything else.

File storage on ZFS with regular snapshots is an efficient way of mitigating ransomware attacks.

ZFS offers safe and secure ways of transferring data between hosts. Its block–based differential send/receive is faster than anything else I have seen on the market, and the snapshoting ensures that source data is not modified during transfer.

For environments where ZFS is not a viable option, rsync provides a good way of transferring data between hosts.

As for conventional backup handling, I have good experiences with Bacula. The backups are handled centrally, and it can back up a wide range of platforms. It also scales well, from backing up a single machine to hundreds or thousands of machines, and it can handle a variety of different backup media.

Storage and backup

  • ZFS–backed storage
  • Rsync
  • Bacula: a client/server–based network backup program

SQL

SELECT books.id, books.name, shelves.id AS shelf_id, shelves.name AS shelf_name, rooms.id AS room_id, rooms.name AS room_name FROM books INNER JOIN shelves ON books.shelf_id = shelves.id INNER JOIN rooms ON shelves.room_id = rooms.id WHERE shelves.is_accessible = true AND books.is_readable = true;

SQL databases

I have extensive experience with administrating database servers and writing SQL queries.

I can help with both building databases from scratch, and modifying and optimizing existing databases.