Configure HTTP probes

HTTP probes hit a URL on the configured interval. The reported value is response_time_ms for successful requests, or no_data with a reason code when the request fails (timeout, connection refused, body mismatch, unexpected status).

Configuration shape

{
  "url": "https://api.example.com/healthz",
  "method": "GET",
  "expected_status": 200,
  "timeout_ms": 5000,
  "headers": { "User-Agent": "observer-agent" },
  "body_match": "ok",
  "follow_redirects": true,
  "verify_tls": true
}

Field reference

Field	Default	Notes
`url`	required	Full URL including scheme.
`method`	`GET`	One of `GET`, `HEAD`, `POST`, `PUT`, `PATCH`, `DELETE`, `OPTIONS`.
`expected_status`	`200`	Single integer or array. The probe matches if the response code is in the set.
`timeout_ms`	`5000`	Aborts the request when exceeded. Reports `ETIMEDOUT`.
`headers`	none	Extra request headers. Common use: API key for protected endpoints.
`body_match`	none	Optional substring match against the first 4KB of the response body. Mismatch reports `body_mismatch`.
`follow_redirects`	`true`	When `false`, redirect responses count against `expected_status`.
`verify_tls`	`true`	When `false`, the probe accepts invalid TLS certificates. Useful for self-signed internal endpoints.

Reason codes

The reason field on no_data results uses values from the HTTP client and Node socket layer:

ETIMEDOUT: request exceeded timeout_ms.
ECONNREFUSED: connection refused at the TCP layer.
ENOTFOUND, EAI_AGAIN: DNS resolution failed.
unexpected_status:<code>: status code not in expected_status.
body_mismatch: body_match was set and the response body did not contain it.

Threshold examples

Goal	Healthy	Unhealthy
Endpoint reachable, fast	`under 500`	`over 2000`
Endpoint reachable	`under 5000`	`over 10000`

For pure reachability with no latency requirement, set the unhealthy threshold equal to the timeout and rely on no_data for failures.