Change Virtual Host of RabbitMQ at runtime for Django/Celery

Today I needed to route tasks to a virtual host on RabbitMQ from a regular Django app with the aid of Celery.

To achieve this, you need to access the settings dictionary like so:

from django.conf import settings

Let’s view the full list of what it contains.

dir(settings)

You will now see the key BROKER_URL. This is what you need to change.

Set this to some other URL that contains the virtual host that you want to route your task to just before you call the task.

settings.BROKER_URL = 'amqp://admin:admin@192.168.2.109:5672/vhost'
# make call to task
# my_task.send_email.delay()
# reset settings.BROKER_URL

vhost represents the virtual host you want to send the task to.

Kindly note that changing this URL at runtime is not encouraged and do remember to reset the settings.BROKER_URL back to what it was before you called the task

I hope this info helped.

Ruby Blocks Explained

Hit this url if you really wanna understand all about Ruby blocks and how to better understand them

List open ports on Linux

I found this snippet of code useful when trying to figure out which of the servers on your box are actually running by observing the ports that are open.

netstat -lntu

Mayan-Edms IOError: [Errno 13] Permission denied

Here is what to do when faced with an error resembling the following:

/usr/share/mayan-edms/lib/python2.7/site-packages/ to pythonpath.
Traceback (most recent call last):
File "/usr/share/mayan-edms/lib/python2.7/site-packages/mayan/wsgi.py", line 16, in 
application = get_wsgi_application()
File "/usr/share/mayan-edms/lib/python2.7/site-packages/django/core/wsgi.py", line 13, in get_wsgi_application
django.setup(set_prefix=False)
File "/usr/share/mayan-edms/lib/python2.7/site-packages/django/__init__.py", line 27, in setup
apps.populate(settings.INSTALLED_APPS)
File "/usr/share/mayan-edms/lib/python2.7/site-packages/django/apps/registry.py", line 85, in populate
app_config = AppConfig.create(entry)
File "/usr/share/mayan-edms/lib/python2.7/site-packages/django/apps/config.py", line 116, in create
mod = import_module(mod_path)
File "/usr/lib/python2.7/importlib/__init__.py", line 37, in import_module
__import__(name)
File "/usr/share/mayan-edms/lib/python2.7/site-packages/mayan/apps/checkouts/apps.py", line 29, in 
from .tasks import task_check_expired_check_outs # NOQA
File "/usr/share/mayan-edms/lib/python2.7/site-packages/mayan/apps/checkouts/tasks.py", line 8, in 
from lock_manager.runtime import locking_backend
File "/usr/share/mayan-edms/lib/python2.7/site-packages/mayan/apps/lock_manager/runtime.py", line 5, in 
locking_backend = import_string(setting_backend.value)
File "/usr/share/mayan-edms/lib/python2.7/site-packages/django/utils/module_loading.py", line 20, in import_string
module = import_module(module_path)
File "/usr/lib/python2.7/importlib/__init__.py", line 37, in import_module
__import__(name)
File "/usr/share/mayan-edms/lib/python2.7/site-packages/mayan/apps/lock_manager/backends/file_lock.py", line 25, in 
open(lock_file, 'a').close()
IOError: [Errno 13] Permission denied: u'/tmp/mayan_locks.tmp'
unable to load app 0 (mountpoint='') (callable not found or import e

Simply change the permission of the /tmp folder like so:

chown -R www-data:www-data /tmp/

That should fix the issue.

Thoughts ?

VIm – Go setup

After scratching my head to baldness, I found this link that really helped me setup VIm for Golang programming.

https://github.com/fatih/vim-go-tutorial#quick-setup

The first few paragraphs should help you get up to speed in a matter of minutes.

Go ahead. Try it !

Add class attribute to Django form fields

Having realized how hard it is to manually write code to display django form, I decided to implement a small hack to enable me attach bootstrap classes to django form fields.

 

1. Create a python file under the templatetags folder in your django project.
2. In this file (named say, my_form_tag.py) add the following:

   from django.template import Library
   
   register = Library()
   
   @register.filter(name='addclass')
   def addclass(field, class_attr):
       return field.as_widget(attrs={'class': class_attr})
   

3. In the rendered html template, load the file with the template tags and use it to relike so

<html>

{% load staticfiles %}
{% load my_form_tag %}

4. Use the tag in the body of your page

   {{ field | addclass:"form-control" }}

Docker: re-exec error: exit status 1: output: write /var/lib/mysql/ibdata1: no space left on device

I usually find myself in a very annoying situation where my docker containers keeping getting full anytime I am building mysql containers.

Here are the series of steps I employ to get myself rid of such issues.

boot2docker config > ~/.boot2docker/profile

change the line with DiskSize from DiskSize = 20000 to 24000
Feel free to increase this number to your choice.

boot2docker poweroff

boot2docker destroy

Eclipse Tomcat not starting in 45 seconds (Solution ?)

In a bid to keep my Java skills alive, I decided to start from the ground up, from Servlets to EJB’s using Eclipse. I hit a stumbling block anytime I tried to start the Tomcat Server v. 7. I pops up this annoying “Tomcat not starting in 45 seconds”. One may be tempted to increase the timeout period but that barely solves the problem.

Try the following first.

1. http://crunchify.com/step-by-step-guide-to-setup-and-install-apache-tomcat-server-in-eclipse-development-environment-ide/

2. https://sansatechnology.wordpress.com/2011/09/26/how-to-fix-eclipse-tomcat-not-starting-in-45-seconds/

If the above fails, do the following.

1. Setup your eclipse + tomcat as per point 1.

2. Now eclipse views the Server as a project. So click on “Servers” under the Project Explorer Tab.

3. Click on the drop down part of the “Run button” and choose the first option like the image below.

4. Did it work ?

morgan deprecated undefined format: specify a format

Learning about middleware with node.js I encountered a problem.
When I installed morgan, and run the following piece of code I get an error.

var express = require("express");
var http = require("http");
var logger = require("morgan");
var app = express();


// Logging middleware
app.use(logger());


// Send "hello world"
app.use(function(request, response) {
    response.writeHead(200, {"Content-Type": "text/plain"});
    response.end("Hello world!\n");
});

http.createServer(app).listen(1337);

The error goes something like

morgan deprecated undefined format: specify a format app.js:13:9

This page seems to suggest that I have to specify the format of the output. So change from

app.use(logger());

to

app.use(logger("combined"));

Errrh, you are welcome.

Python Decorators: A cool breeze tutorial

When I started learning Java EE, I liked the dependency injection that was used to create EJB and Managed beans. Anytime you wanted to inject some dependency just use @SomeComponent and you have it.

Now I am having to use Python. The same syntactic sugar is being used here. But this time, it is for extending the functionality that a function gives. I really thought I could not comprehend this concept but this blog did a very good job of dissecting the issue.

I went like,” Ohhh, these people have introduced yet another difficult to understand concept. Ah, can’t they just stick to simple python stuff. They just want to worry mankind. ”

So after going through this blog I am stunned. Check it out.