Occasionally I have to do scripting work outside of our config management tool of choice, Juju 1 - eg. for bootstrapping or one-off jobs. I had used Fabric version 1 previously (as well as Plumbum) for those, and was looking at Fabric 2 (respectively it's sidekick Invoke) now.
Overview: Concurrency with Actors
Actor systems model concurrency with actors. In such a system, actors are independent objects that communicate asynchronously with each other via message passing.
An actor can:
Receive and send messages asynchronously
Change private state
Create new actors
Each actor has an address under which it can …
TIL that the Python
requestslibrary is able to dump request/response details to the debug log - quite useful for development and debugging of http clients.
Switch it on with something like this:
import requests import logging try: # for Python 3 from http.client import HTTPConnection except ImportError: from httplib …
Or: digging into Openstack Neutrons' packet filtering bowels
The other day I had to track down weird behaviour with Neutron security groups in one of our clouds, and thought to share notes on debugging those and on Neutron networking in general 1.
Compute node neutronics
Recall that on a compute …
I love Ceph to pieces! I don't love it's docs that much though, and I find the multi-level subcommands unintuitive at times. Quick, is it "ceph pg query x.y" or "ceph pg x.y query"? There's some good docs out there, but to me they feel scattered and it's …
It's been awhile, but finally I've found some time to play with Clojure again.
Now on for some more functional programming techniques: partials, closures, higher order functions, and so on.
Recap: composite types as functions
Composite types can be used as functions of their elements, I wrote about this previously …
I'm now reaching Pt. III of "The Joy of Clojure". The first part is about immutability and lazy evaluation.
Recap: Benefits of Immutability
Values are set in constructors and don't change thereafter. Makes it easier to debug and reason about programs. Implementing invariants is easier: invariants only need to be …
Last time I've explored scalar data types. There are a lot of details to discover there, but on the whole that was dry stuff.
Now for something a bit more complex: collection data types (putting the List in Lisp).
Persistence and Terminology
Immutable sequences are called persistent in The Book …
When I was a System Integrator in Zug, I really learned to love log files. Indispensable for troubleshooting; and over time you learned to visualize the internal state of the trading programs just by looking at the traces.
However, most of those logs were local. The most critical log messages …
Now for some more details on fundamental data types. The fourth chapter of "The Joy of Clojure" 2nd ed. deals with some scalar data type topics. I'll cover integer overflow, keywords, symbols, metadata, regular expressions, and others.
Overflow and Promotion
By default, we get Longs:
user> (def regular 23) #'user …