Document erlang cookie rotation

Author: YuryHrytsuk

services/rabbit/Makefile

@@ -30,5 +30,5 @@ rabbitmq.conf: rabbitmq.conf.j2 .env venv
 	# generate $@
 	@$(call jinja, $<, .env, $@)
 
-docker-compose.yml: docker-compose.yml.j2 .env rabbitmq.conf erlang.cookie.secret venv
+docker-compose.yml: docker-compose.yml.j2 .env rabbitmq.conf erlang.cookie.secret venv $(VENV_BIN)/j2
 	@$(call jinja, $<, .env, $@)

services/rabbit/README.md

@@ -16,5 +16,6 @@ Source: https://www.rabbitmq.com/docs/upgrade#maintenance-mode
 
 ## Rotating erlang cookie (zero-downtime)
 
-https://github.com/rabbitmq/rabbitmq-server/issues/14390
-https://github.com/rabbitmq/rabbitmq-server/discussions/9784
+In our case, a full stop of rabbit cluster is required (it means downtime). Nodes shall be started from scratch with a new erlang cookie. If zero-downtime update is an absolute must, blue-green deployments is a way to go according to core developers (see sources)
+
+Source: https://github.com/rabbitmq/rabbitmq-server/discussions/14391

services/rabbit/docker-compose.yml.j2

@@ -7,6 +7,10 @@ services:
     init: true
     # https://docs.docker.com/reference/cli/docker/service/create/#create-services-using-templates
     hostname: {% raw %}"{{.Service.Name}}"{% endraw %}
+    deploy:
+      placement:
+        constraints:
+          - node.labels.rabbit0{{ ix }} == true
     environment:
       RABBITMQ_DEFAULT_USER: ${RABBIT_USER}
       RABBITMQ_DEFAULT_PASS: ${RABBIT_PASSWORD}