HAProxy Alerts with WebHooks

I want to be notified immediately when one of the backend servers behind my HAProxy instance goes down. HAProxy offers alerting functionality, but only via SMTP: when a backend goes down it sends an email to a list of recipients via an SMTP server you provide. Unfortunately, email isn’t an ideal mechanism for real-time notification, and I don’t have an SMTP server accessible from my HAProxy instance. In this post, I’ll show my setup of HAProxy posting its alerts to a Slack channel and the Pushover push notification service, using smtp-http-proxy and AWS Lambda.