overdue

Overdue is a small HTTP check-in monitor.

It exposes one check-in endpoint. As long as something calls that endpoint within the configured interval, the monitor stays healthy. When the expected check-in is missed, Overdue first marks the monitor as overdue. If the check-in still does not arrive before the alerting delay elapses, Overdue sends notifications.

The service is intentionally minimal:

• one check-in monitor
• one configurable check-in route
• JSON status endpoint
• optional bearer-token auth
• webhook notifications
• email notifications
• built-in and custom Go templates

How it works

Overdue tracks a single check-in monitor with four phases:

stateDiagram-v2
    [*] --> scheduled
    scheduled --> awaiting: first check-in
    awaiting --> awaiting: check-in before expectedBy
    awaiting --> overdue: expectedBy reached
    overdue --> awaiting: check-in before alertingAt
    overdue --> alerting: alertingAt reached / queue alerting notification
    alerting --> awaiting: check-in received / queue resolved notification when enabled

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Phase	Meaning
scheduled	No check-in has been received yet. No deadline is active.
awaiting	A check-in was received and the next deadline is scheduled.
overdue	The expected check-in deadline passed. The alerting delay is now running.
alerting	The alerting delay passed and an alerting notification was created.

The two timing settings are separate:

Setting	Meaning
--expected-every	Maximum allowed time between check-ins.
--alerting-delay	Extra time after the expected deadline before notifying.

Quick start

Start Overdue with Docker:

docker run --rm -p 8080:8080 \
  -e OVERDUE__EXPECTED_EVERY=1m \
  -e OVERDUE__ALERTING_DELAY=10s \
  ghcr.io/containeroo/overdue:latest

Send a check-in:

curl -XPOST http://localhost:8080/check-in

Read the current status:

curl http://localhost:8080/status

Read detailed status:

curl 'http://localhost:8080/status?details=true'

Docker Compose and Kubernetes manifests are available in deploy/. See docs/deployment.md for deployment notes.

Configuration

Overdue can be configured with CLI flags or environment variables. CLI flags override environment values.

Required settings:

Flag	Environment variable	Description
--expected-every	OVERDUE__EXPECTED_EVERY	Maximum allowed time between check-ins.
--alerting-delay	OVERDUE__ALERTING_DELAY	Extra time after the expected deadline before notifications fire.

Core settings:

Flag	Environment variable	Default	Description
--listen-address	OVERDUE__LISTEN_ADDRESS	:8080	HTTP server listen address.
--route-prefix	OVERDUE__ROUTE_PREFIX	empty	Path prefix to mount the service under.
--check-in-name	OVERDUE__CHECK_IN_NAME	default	Name of the check-in monitor used in notifications.
--check-in-path	OVERDUE__CHECK_IN_PATH	/check-in	Route used to receive check-ins.
--start-active	OVERDUE__START_ACTIVE	false	Activate the monitor at startup instead of waiting for the first check-in.
--response-details	OVERDUE__RESPONSE_DETAILS	false	Return detailed timing fields from check-in responses by default.
--auth-token	OVERDUE__AUTH_TOKEN	empty	Optional bearer token required for check-in and status requests.
--debug	OVERDUE__DEBUG	false	Enable debug logging.
--log-format	OVERDUE__LOG_FORMAT	json	Log format: json or text.

Environment variables use the OVERDUE__ prefix. Flag names are uppercased and dashes become underscores.

Dynamic notification flags include the target name:

--webhook.ops.url                  -> OVERDUE__WEBHOOK_OPS_URL
--email.primary.smtp-host          -> OVERDUE__EMAIL_PRIMARY_SMTP_HOST

See docs/configuration.md for the full configuration reference.

Notifications

Overdue supports multiple named webhook and email notification targets.

Minimal Slack incoming webhook example:

docker run --rm -p 8080:8080 \
  -e OVERDUE__EXPECTED_EVERY=1m \
  -e OVERDUE__ALERTING_DELAY=10s \
  -e OVERDUE__WEBHOOK_OPS_URL="$SLACK_WEBHOOK_URL" \
  -e OVERDUE__WEBHOOK_OPS_TEMPLATE=builtin:slack-incoming-webhook \
  -e OVERDUE__WEBHOOK_OPS_SEND_RESOLVED=true \
  ghcr.io/containeroo/overdue:latest

If no notification targets are configured, Overdue still runs and records status, but sends no notifications.

See docs/notifications.md for webhook, Slack, and email examples.

Templates

Notification payloads are rendered with Go templates. Overdue includes built-in templates for HTML email, Slack incoming webhooks, and Slack chat.postMessage.

Use a built-in template:

-e OVERDUE__WEBHOOK_OPS_TEMPLATE=builtin:slack-incoming-webhook

Custom templates can be mounted into the container and referenced by path:

-e OVERDUE__WEBHOOK_OPS_TEMPLATE=/etc/overdue/slack.tmpl

Webhook templates must render valid JSON. Email templates may render text or HTML.

See docs/templates.md for built-in templates, template data, and helper functions.

HTTP API

Method	Path	Description
GET, POST	/check-in	Records a check-in.
GET	/status	Returns the monitor state.
GET	/version	Returns build information.
GET, POST	/healthz	Returns a health response.

The check-in path is configurable with --check-in-path. The other routes are mounted under --route-prefix when a route prefix is configured.

See docs/api.md for response examples and route prefix details.

More documentation

• Configuration
• Notifications
• Templates
• HTTP API
• Deployment
• Development

License

This project is licensed under the Apache 2.0 License. See the LICENSE file for details.