Posts

We’ve written Herodotus1 as a lightweight logger to solve some very specific problems we had in our tests, but we don’t think they are unique to us so we’re going to share with you what we have done and why. Logging to the standard output and the main problem we faced The problem we are trying to solve is one of readability. All good logs are human readable, as when something has gone wrong to the point of a human needing to look in the logs and piece together what has happened we don’t want to make that more difficult than is needed. Now, there are things out there that will help you manage your logs (for example, OpenSearch provides a fantastic toolkit for exploring a large volume of logs), these are often looking at things on a grander scale than we are. There are always going to be times where you want your system to just leave a little message wherever it is currently running, which is why we are looking at things that are logging to the standard output on whatever device they are running. Specifically in our case, we are looking at the output of an automated test pack. ...

Testing what a Ruby process writes to STDOUT. Ruby’s relationship with STDOUT Ruby has two built-in values that represent the system’s standard output stream: The constant STDOUT The global variable $stdout The Ruby documentation, describes STDOUT as the standard output, and $stdout and the current standard output. If you want to change the stream that this Ruby process sends its output to, you can change the value of $stdout Hello StringIO Given an RSpec test pack, I should be able to use an output matcher, but I couldn’t get this to reliably work across tests for my system. However, the standard library includes an IO-like object for strings, StringIO, which must be explicitly required. ...

Introduction Dead letter queues (DLQ) are often used to catch items that have not been successfully processed or delivered when using queue 1 based integration patterns. Typically engineering teams will want to be alerted quickly to the presence of items on a dead letter queue so they can do something about it e.g. redrive messages back to a source queue, inspect the messages for further understanding of an issue etc. In this post we’ll discuss how we lost messages that had been placed on a dead-letter queue, how we have learnt from this experience and what we have done to improve our processes. ...

Over the last few years we’ve invested in tooling and processes that make heavy use of JSON Schema. What is JSON Schema? JSON Schema is a standard vocabulary that allows developers to describe data formats. At the DVLA we use these definitions in various ways e.g. to generate human friendly documentation, to generate code based on the models, to describe parts of our API interfaces and to validate data objects. ...