# One result PER UNIT, not one for the host. A host running four services
    # needs four endpoints: a single red light would tell you "something on vipy
    # is down" without saying which, and that is the question you actually have.
    #
    # Keys are host-qualified because unit names collide - caddy runs on four
    # machines. Gatus builds the key as sanitize(group)_sanitize(name), so
    # group "services" + name "vipy/caddy" becomes services_vipy-caddy.
    local prefix="{{ healthcheck_units_key_prefix }}"
    local down=""

    for unit in {{ healthcheck_units | join(' ') }}; do
        local state substate
        state=$(systemctl is-active "$unit" 2>/dev/null || true)
        substate=$(systemctl show -p SubState --value "$unit" 2>/dev/null || true)

        if [ "$state" = "active" ]; then
            report_key "${prefix}-${unit}" "true" "${unit} active (${substate:-running})"
        else
            # `failed` and `inactive` are different stories: one crashed, one was
            # stopped. Both are down, but the message should say which.
            local detail="${unit} is ${state:-unknown}"
            [ "$state" = "failed" ] && detail="${detail} (${substate:-failed})"
            report_key "${prefix}-${unit}" "false" "$detail"
            down="${down}${down:+, }${unit}=${state:-unknown}"
        fi
    done

    if [ -n "$down" ]; then
        MESSAGE="down: ${down}"
        return 1
    fi
    MESSAGE="all {{ healthcheck_units | length }} units active"
    return 0