Software Engineer

Write Your Own Load Balancer: A worked Example

I was out walking with a techie friend of mine I’d not seen for a while and he asked me if I’d written anything recently. I hadn’t, other than an article on data sharing a few months before and I realised I was missing it. Well, not the writing itself, but the end result. In the last few weeks, another friend of mine, John Cricket , has been setting weekly code challenges via linkedin and his new website, https://codingchallenges.fyi/ . They were all quite interesting, but one in particular on writing load balancers appealed, so I thought I’d kill two birds with one stone and write up a worked example. You’ll find my worked example below. The challenge itself is italics and voice is that of John Crickets. The Coding Challenge https://codingchallenges.fyi/challenges/challenge-load-balancer/ Write Your Own Load Balancer This challenge is to build your own application layer load balancer. A load balancer sits in front of a group of servers and routes client requests across all of the serv...

Catalina-Ant for Tomcat 7

I recently upgraded from Tomcat 6 to Tomcat 7 and all of my Ant deployment scripts stopped working. I eventually worked out why and made the necessary changes, but there doesn’t seem to be a complete description of how to use Catalina-Ant for Tomcat 7 on the web so I thought I'd write one. To start with, make sure Tomcat manager is configured for use by Catalina-Ant. Make sure that manager-script is included in the roles for one of the users in TOMCAT_HOME/conf/tomcat-users.xml . For example: <tomcat-users> <user name="admin" password="s3cr£t" roles="manager-gui, manager-script "/> </tomcat-users> Catalina-Ant for Tomcat 6 was encapsulated within a single JAR file. Catalina-Ant for Tomcat 7 requires four JAR files. One from TOMCAT_HOME/bin : tomcat-juli.jar and three from TOMCAT_HOME/lib: catalina-ant.jar tomcat-coyote.jar tomcat-util.jar There are at least three ways of making the JARs available to Ant: Copy the JARs into th...

RESTful Behaviour Guide

I’ve used a lot of existing Representational State Transfer (REST) APIs and have created several of my own. I see a lot of inconsistency, not just between REST APIs but often within a single REST API. I think most developers understand, at a high level, what a REST API is for and how it should work, but lack a detailed understanding. I think the first thing they forget to consider is that REST APIs allow you to identify and manipulate resources on the web. Here I want to look briefly at what a REST API is and offer some advice on how to structure one, how it should behave and what should be considered when building it. I know this isn’t emacs vs vi, but it can be quite contentious. So, as Barbossa from Pirates of the Caribbean said, this “...is more what you’d call ‘guidelines’ than actual rules.” Resources & Identifiers In their book, Rest in Practice - Hypermedia and Systems Architecture (‎ISBN: 978-0596805821), Jim Webber, Savas Parastatidis and Ian Robinson describe resour...

Paul Grenyer

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