When building services with etcd, one of the best features of etcd is watchers. It allows developers to create applications such that when a dataset is changed, the watcher for that dataset on another system receives the notification and performs user-specified action. A simple use case is a user has a program using etcd watchers to monitor the stock market and sell (user-defined action) if their stock of interest falls below price $X.

There are error failures that are not automatically covered with an etcd cluster such as network connectivity issues, DC outage, and cloud infrastructure maintenance. The talk consists of the following:
- what watchers are
- how to build your services using heartbeat key for monitoring etcd watchers
- perform locking on watchers to prevent race conditions
- caching data locally for your service to keep running until the etcd cluster is back up.