0016. "target" as the domain vocabulary and `Target.Key` identity

• Status: Accepted
• Date: 2026-07-10

Context

The stored identifier for a monitored thing is protocol//address/servername — not a host: one host/address can expose several distinct monitored things on different ports, protocols or server names. So host names less than the identity encodes, and the key column shared across alert_state, probe_log, alert_log and notification_outbox is too generic to tell a reader which key it is. The domain vocabulary and the identity contract are one question: what is a monitored thing called, and what makes two of them the same?

Decision

The canonical domain noun is “target” — chosen over host (too narrow: protocol//address/servername is more than a host) and endpoint (the interim front-runner). The config type is Target and the identity is Target.Key(), which returns protocol + "//" + address + "/" + servername.

That format is a stable contract: it is the dedup key, the alert_state primary key, and the join key across every table, so it must not change across versions.

Consequences

• Target.Key()’s components define target identity: editing a target’s notifiers or warning_days/critical_days keeps the same key (so it inherits dedup state and last_alert_at — a notifier switch does not re-alert; 0006 ), while editing address/protocol/ servername changes the key, making it a remove + add (state pruned, metric series deleted, fresh start).
• The identity components line up with the frozen Prometheus identity label family (0015 ), so the exported labels and the DB key can’t drift apart.
• One consistent word (“target”) from config to code to docs to the certel check CLI.

Alternatives considered

• host. Rejected: names less than the key encodes; misleads about one-host, many-targets.
• endpoint. The deferred front-runner (it matches “protocol + address + SNI”), but “target” won as the term that also reads naturally in the CLI and user-facing prose.

References

• internal/config/config.go (Target.Key, config.go:387), docs/schema.dbml.