[__jitsi_meet] Add --abort-conference-count parameter

Only has an effect if the prometheus exporter is enabled and if it is not
empty (default).
If at least this many conferences are active on the server, the type will
bail out before making any changes.
This is useful if you want to avoid service disruptions due to e.g. an SLA.

Sponsored by:	camilion.eu

type/__jitsi_meet/explorer/jitsi-status

@@ -0,0 +1,6 @@
+#!/bin/sh -eu
+
+if [ ! -f "${__object}/parameter/disable-prometheus-exporter" ]; then
+	# TODO: detect curl / depend on it?
+	curl -s localhost:9888/metrics
+fi

type/__jitsi_meet/man.rst

@@ -47,6 +47,14 @@ NOTE: This type currently does not deal with setting up coturn.
 
 OPTIONAL PARAMETERS
 -------------------
+abort-conference-count
+    Only has an effect if the prometheus exporter is enabled and if it is not
+    empty (default).
+    If at least this many conferences are active on the server, the type will
+    bail out before making any changes.
+    This is useful if you want to avoid service disruptions due to e.g. an SLA.
+
+
 turn-secret
     The shared secret for the TURN server.
 

type/__jitsi_meet/manifest

@@ -10,6 +10,20 @@ case "${os}" in
 	;;
 esac
 
+current_conferences="$(cat "${__object}/explorer/jitsi-status" | grep -E "^jitsi_conferences[[:space:]]" | cut -d ' ' -f 2)"
+
+ABORT_CONFERENCE_COUNT="$(cat "${__object}/parameter/abort-conference-count")"
+
+if [ -n "${current_conferences}" ] && [ -n "${ABORT_CONFERENCE_COUNT}" ] && \
+	[ "${ABORT_CONFERENCE_COUNT}" -le "${current_conferences}" ]; then
+	cat <<-EOF
+Early bail out was requested when at least ${ABORT_CONFERENCE_COUNT} conferences are taking place.
+There are currently ${current_conferences} active conferences.
+
+Try again at a later time or remove or increase --abort-conference-count
+	EOF
+	exit 1
+fi
 
 JITSI_HOST="${__target_host}"
 if [ -f "${__object}/parameter/jitsi-version" ]; then

type/__jitsi_meet/parameter/optional

@@ -1,3 +1,4 @@
+abort-conference-count
 jitsi-version
 turn-secret
 turn-server