Create a Cassandra cluster with OpsCenter on Amazon EC2

Today I played a little with Cassandra on Amazon EC2. It was a very user friendly and pleasant experience to deploy a cluster with 2 nodes in one region using DataStax OpsCenter.

First I started a m1.small instance in Amazon EC2 where I installed OpsCenter. For this I chose Centos 6, the official AMI. Before starting to install OpsCenter, we need to configure the firewall in order to be able to access it. In AWS console, under the Security group, there is “CentOS 6 -x86_64- – with Updates-6 – 2014-09-29-AutogenByAWSMP-“. We need to righ-click on it and Edit inbound rules. Here we add a new Custom TCP Rule with port 8888 and the Source IP: My IP.

Anyway, I noticed that the instance has also an iptables firewall and the port 8888 is not open. So, on the instance I did:

iptables -I INPUT 4 -p tcp --dport 8888 -j ACCEPT
iptables-save | tee /etc/sysconfig/iptables

Now, we can install OpsCenter. All you need to do is to follow the installation guide for RPM package from DataStax:

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Install SSL certificate for Nginx

Recently I bought an SSL certificate for this blog from MegaSSLStore. My website is hosted on a FreeBSD machine and served by Nginx web server. In order to install the certificate on this machine, I downloaded from MegaSSLStore the certificate and CSR+private key and I copied them on my server in /usr/local/etc/nginx/ssl

# scp -P22 *

root@RTU001 /usr/local/etc/nginx/ssl # ls -lh
total 32
-r-------- 1 root wheel 5.5K Dec 14 11:39
-r-------- 1 root wheel 1.9K Dec 14 11:39
-r-------- 1 root wheel 1.1K Dec 14 11:39
-r-------- 1 root wheel 1.7K Dec 14 11:39

Because I have an .crt certificate and also a ca-bundle I need to combine these two files in one certificate:

cd /usr/local/etc/nginx/ssl
cat >

After this, I changed the nginx website configuration file, in order to redirect all the traffic that is coming on http (port 80) on https (port 443).

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Monitor an error log with python and RabbitMQ

Nowadays there are many professional solutions to monitor your application for the errors. Some web frameworks have even build-in tools or support plugins to catch the programming exceptions and act accordingly.

Anyway, I wanted just to build a simple proof of concept how to monitor the web server error file and, when an event occurs and the file is changed, the monitoring script should send out an email. To monitor the log file I used pyinotify python module. This is an implementation on top of inotify, offering an easy interface to interact with the changes of the filesystem.

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git tags use

Today I had to read about git tags in order to be able to explain in a better way why somebody would use tags and for what. The old (and still good) git workflow explains very well how to develop using branches but doesn’t explain too well why we create the tags and how should be used on production. It just saying “that commit on master must be tagged for easy future reference to this historical version”. If you followed that guide and now you are ready to go live with your code changes, you maybe wonder what should you do with the tag? Why did you create it. Some people would say, just leave it there, maybe somebody, in a shiny day will take a look to it. Just go to production and do git pull origin master. But I don’t think this is the purpose of the tag.

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