Add "vm_memory_high_watermark" to the generated config, sourced from the value of the "memory.limit_in_bytes" cgroup restriction

Author: tianon

docker-entrypoint.sh

@@ -212,6 +212,14 @@ if [ "$1" = 'rabbitmq-server' ] && [ "$haveConfig" ]; then
 		"{ loopback_users, $(rabbit_array) }"
 	)
 
+	# https://github.com/rabbitmq/rabbitmq-website/pull/96/files
+	# "If the absolute limit is larger than the installed RAM or available virtual address space, the threshold is set to whichever limit is smaller."
+	# specifically, if a memory limit isn't supplied to the container and "memory.limit_in_bytes" is thus an enormous constant, RabbitMQ will ignore it and use maximum available memory or address space instead
+	if [ -r /sys/fs/cgroup/memory/memory.limit_in_bytes ]; then
+		memLimit="$(< /sys/fs/cgroup/memory/memory.limit_in_bytes)"
+		rabbitConfig+=( "{ vm_memory_high_watermark, { absolute, $(( memLimit / 1024 / 1024 )) } }" )
+	fi
+
 	if [ "$haveSslConfig" ]; then
 		IFS=$'\n'
 		rabbitSslOptions=( $(rabbit_env_config 'ssl' "${sslConfigKeys[@]}") )