TornadoWeb is a great non-blocking web server written in Python and Boto3 is the Amazon Web Services (AWS) SDK for Python, which allows developers to write in a very easy manner software that makes use of Amazon services like S3. Unfortunately boto3 S3 wrapper is blocking and if you would just use it out of the box in a Tornado application it will block the main thread because it uses a synchronous HTTP client.
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.
Let’s assume we want to download a file (or to do some tasks) to every 5 seconds, but the condition is to not do the same task twice or more times at the same moment, even if takes more than 5 seconds. For example, we have a to download a file and this will take 8 seconds. Also, if takes more than 5 seconds, it should not wait until the next iteration, to start again (3 seconds more), but will start the download immediately.
So, the traditional cronjob/lock file combination was not suitable for my case.
REST Anti-Patterns – A lot of people (or companies) pretend to have a REST API. Read this article and you will understand that not all the API’s that implement GET and POST methods are REST APIs. It is an old article (from 2008), but still valid.