We’ve been recently running rest APIs on active-active server pairs (docker containers running on pairs of VMs on separate hosts) with postgres-BDR (multi-master bidirectional replication) for fault-tolerant storage and a pair of fault-tolerant HAProxy instances for incoming request routing. This is a robust setup which provides zero downtime during rolling updates or hardware maintenance or failure. However, clustering scheduled jobs (i.e. ensuring that scheduled jobs execute exactly once) becomes a problem in this configuration. Multi-master replicated databases avoid a single point of failure but they are not suitable for use with database-based clustered schedulers like Quartz, so we needed to consider other options. There are complex clustered job schedulers, but we wanted to keep it simple and use Linux crond for scheduling. We finally settled on using keepalived to maintain a single master across the cluster[…]

We live in an old house, on three levels. Its always been a challenge to achieve consistent wifi coverage throughout the house. We neglected to install ethernet cabling when we renovated and have been struggling with wifi issues ever since. We tried power-line networking (Devolo, TP-Link) and, although it worked most of the time, it provided very inconsistent performance and it was impossible to figure out why. We then reverted to a central wireless router and range extenders (Apple, TP-Link). Coverage was pretty bad in many parts of the house. Last weekend, we installed the AmplifiHD mesh networking system from Ubiquiti and we finally have the full performance of our internet provider (40-60Mbps LTE, depending on the time of day) from any or[…]