Category: Sysadmin

System administration is a special are of IT. It also has a special place in my heart. It is an interesting mixture of all the other disciplines, both common across the whole industry, and at the same time unique for each person, company, and geographical location. When I have something to say or share about system administration, I use this category.

YANG – A Data Modeling Language for the Network Configuration Protocol (NETCONF)

In the spirit of validating everything against a schema (validating JSON, validating CSV), here is another option – YANG:

YANG is a data modeling language for the definition of data sent over the NETCONF network configuration protocol. The name is an acronym for “Yet Another Next Generation”. The YANG data modeling language was developed by the NETMOD working group in the Internet Engineering Task Force (IETF) and was published as RFC 6020 in October 2010. The data modeling language can be used to model both configuration data as well as state data of network elements. Furthermore, YANG can be used to define the format of event notifications emitted by network elements and it allows data modelers to define the signature of remote procedure calls that can be invoked on network elements via the NETCONF protocol. The language, being protocol independent, can then be converted into any encoding format, e.g. XML or JSON, that the network configuration protocol supports.

YANG is a modular language representing data structures in an XML tree format. The data modeling language comes with a number of built-in data types. Additional application specific data types can be derived from the built-in data types. More complex reusable data structures can be represented as groupings. YANG data models can use XPATH expressions to define constraints on the elements of a YANG data model.

Like many other standards, formats, and tools developed by very smart people, YANG can be used for much more than just networking configuration.  If you data and states fit into its model, give it a try.

Here are a few resources that you might find useful in the process:

Listing, Iterating, and Loading JSON in Ansible Playbooks

Listing, Iterating, and Loading JSON in Ansible Playbooks – for those days when you need to offload part of your configuration onto external JSON files, but don’t have a spare day to try, fail and repeat.

AWS IAM Policies in a Nutshell

J Cole Morrison wrote an excellent guide into AWS IAM policies. It’s super useful for anyone who have tried implementing IAM policies and failed (or even barely succeeded).

What is an AWS IAM Policy?

A set of rules that, under the correct conditions, define what actions the policy principal or holder can take to specified AWS resources.

That still sounds a bit stiff. How about:

Who can do what to which resources. When do we care?

There we go. Let’s break down the simple statement even more…

Compared to all the AWS documentation one has to dive through, this one is a giant time saver!

Linux utils that you might not know

Linux utils that you might not know covers a few Linux command line utilities that aren’t very famous:

  • column, for “columnating” lists, which is very useful for display of table-like data (think CSV, for example);
  • cal, for displaying calendars;
  • factor, for calculating factors;
  • numfmt, for formatting numbers and converting them to/from human-readable formats;
  • shred, for overwriting the content of a deleted file, making it much more difficult to recover.

HAProxy and Nginx abuse and rate limiting

My brother wrote a follow-up – HAProxy abuse filtering and rate limiting – to his previous post – Nginx rate limit by user agent (control bots).  This is just a tip of the iceberg that we are working with at the office, but it’s pretty cool.

Hopefully, soon enough our Ansible playbooks will be up to date and shareable…