HAProxy option redispatch & backup servers
When we’re creating an API with fault-tolerance, to reduce the number of single points of failure, we often use Postgres BDR, a multi-master database, which allows us to provide two… Read more »
How to migrate large VMWare VMs to remote data-centers using rsync
Using VCenter’s migration over the internet to a remote data-center is often too slow for practical purposes – a 200GB VM may take several hours to move and that may… Read more »
VM disk performance across datastores
Here are some disk performance measurements (made on a Windows 10 VM on vSphere 6.5 with CrystalDiskMark) across different types of datastore (local SSD array, NFS (sync), NFS (async) and… Read more »
Fun with IoT monitoring
To celebrate the successful first year of Powerbot, the algorithmic energy trading company, we decided to build a Powerbot robot which could continuously monitor the status of the Powerbot APIs…. Read more »
Blocking access to an ip address
Sometimes you need to block access to a specific ip address for test purposes – for instance to simulate unavailability of a web-service. Here’s how to do it on macOS… Read more »
Moving Docker container data
If you have created a container without specifying a volume, Docker will create one for you. If you later decide you’d rather have the container’s data somewhere else, you can… Read more »
Repairing a broken Postgres-BDR cluster
Postgres-BDR is an excellent multi-master replication clustering extension for PostgreSQL (https://www.2ndquadrant.com/en/resources/postgres-bdr-2ndquadrant/). We often use it for fault tolerant systems – its asynchronous and uncomplicated to set up (at least if… Read more »
A contact-tracing armband
Current plans for contact-tracing are based around mobile phones, because these have built-in capabilities for location tracking and contact detection. An alternative to mobile phones for contact-tracing would be a… Read more »
The role of statistical scoring models in contact-tracing
Each contact you have with another person potentially infects you with a virus. If the person you have contact with later tests positive for that virus, the contact you had… Read more »
Automated contact-tracing via Smartphone with Bluetooth Low-Energy contact detection
As our team was designing and implementing an open API for COVID-19 contact-tracing, we also created a smartphone app to demonstrate how fully-anonymised automated contact-tracing can be done with a… Read more »