Welcome! Heii On-Call empowers engineering teams with streamlined on-call rotation scheduling, instant iOS/Android alerts, flexible escalation plans, and an extensive set of monitoring tools including synthetic HTTP probes, cronjob check-ins, and API integrations with platforms like Prometheus and Datadog.

This page explains how we monitor the components of our own multi-tier application, and displays the live status of those triggers.

If you'd like to build a similar live status dashboard for your team (and have the on-call engineer get alerts when there's an issue!), sign up and start creating your own triggers.


Our public-facing website is a Ruby on Rails application. We monitor this with a number of Outbound Probes, covering our homepage, a health check endpoint, and key HTTP protocol and subdomain redirects:

Rails Homepage up 391 ms 14s ago
Rails Health Check Controller up 110 ms 9s ago
www to root domain redirect up 162 ms 41s ago
http to https redirect up 16 ms 28s ago
http://www redirect up 10 ms 12s ago

API Server

Our API server is written in Crystal and lives at, receiving check-ins and state changes from your applications and APMs (see our docs). We monitor this with Outbound Probes as well:

API Subdomain Homepage up 214 ms 56s ago
API Subdomain Health Check Endpoint up 99 ms 55s ago

Outbound Prober

Our Outbound Prober is a sharded cluster of Crystal processes. We use an Inbound Liveness trigger to make sure the entire shard space is being probed at all times. We also monitor a diverse control group of popular hosting providers so we can suppress false-positive alerts when it's more likely that our own connectivity is intermittent:

Full Shard Space Coverage checked in 20s ago
Control Group Majority Up and Fresh checked in 20s ago
Outbound Probe Escalator checked in 21s ago

Background Job Queue

We use Sidekiq as a job queue for asynchronous and scheduled background jobs. We have a WorkerHeartbeatJob that hits an Inbound Liveness trigger to verify our scheduler and workers are running continuously:

Worker Heartbeat checked in 21s ago

ToolServ Microservice

We have an internal Crystal microservice that our Rails code calls for use in one-off queries. There are different approaches and tradeoffs to monitoring non-exposed internal services. Since we care that this microservice is accessible from Rails, we're monitoring this internal microservice by pointing an Outbound Probe at a Rails endpoint that makes a call to the ToolServ health check:

ToolServ Health Check up 236 ms 1m0s ago

Deployed Version Convergence

Our production Rails app, API server, Sidekiq workers, Outbound Prober, and ToolServ are all built and deployed from one Git monorepo. While they will be temporarily running different versions during a rolling deployment, all production processes should eventually all be deployed from the same commit ID. We have a job that checks in with an Inbound Liveness trigger if there is exactly one commit ID currently running in production, ensuring we're alerted to any incomplete or inconsistent deployments that don't converge within a few minutes:

Same Git Commit Check checked in 21s ago

Postgres Database

We monitor some housekeeping tasks on our primary Postgres database, such as ensuring successful logical database backups, and verifying the correct state of schema migrations, primarily using Inbound Liveness triggers which get checked-in on success:

Logical Backup checked in 13m11s ago
Postgres Disk Usage Monitor checked in 20s ago
Schema Migrations Up-to-Date (Rails Check) up 169 ms 1s ago
Schema Migrations Up-to-Date (Sidekiq Check) checked in 21s ago

Miscellanous Background Jobs

Many of our on-call schedule rotation features are time-dependent, such as updating who's currently on call. These tasks run as scheduled jobs in Sidekiq. We monitor the completion of these important jobs with Inbound Liveness triggers:

All Shift Changes Notify checked in 21s ago
Schedule Future Shifts checked in 16m29s ago
Session Cleanup checked in 1m14s ago
Shift Cleanup checked in 21m36s ago

External APIs

We monitor critical third-party APIs with scheduled jobs that check in with Inbound Liveness triggers once they verify connectivity and authentication success:

Amazon SES SMTP checked in 55m3s ago
Google Firebase Cloud Messaging API checked in 55m3s ago
Slack API checked in 55m4s ago
Stripe API checked in 55m3s ago
Telegram API checked in 55m3s ago

External Monitoring

We're in a special situation: we can't rely on Heii On-Call to monitor Heii On-Call itself, because we might not get alerted if something in the critical alerting flow breaks! Therefore, we monitor Heii On-Call with three external services running on distinct infrastructure in geographically distributed locations. We then monitor these external services with Inbound Liveness triggers so that we can get alerted if they stop probing our special health check endpoints. As long as one of these is up, we should be notified when any downtime occurs:

External Monitor 1A checked in 16s ago
External Monitor 1B checked in 27s ago
External Monitor 2A checked in 14s ago
External Monitor 2B checked in 19s ago
External Monitor 3A checked in 21s ago
External Monitor 3B checked in 25s ago

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