nixos/rabbitmq: install rabbitmqadmin-ng by default

FC-43451

This uses the HTTP API from RabbitMQ for administrative purposes and
looks quite useful so far.

Since it took me a moment to figure out how to configure a user that can
interact with this tool, I added the setup part to our manual.

Author: Ma27

changelog.d/20250305_120319_fc-24.11-dev_scriv.md

@@ -0,0 +1,19 @@
+<!--
+
+A new changelog entry.
+
+Delete placeholder items that do not apply. Empty sections will be removed
+automatically during release.
+
+Leave the XX.XX as is: this is a placeholder and will be automatically filled
+correctly during the release and helps when backporting over multiple platform
+branches.
+
+-->
+
+### Impact
+
+- [`rabbitmqadmin-ng`](https://www.rabbitmq.com/docs/management-cli) is now installed by default on machines with
+  the `rabbitmq` role.
+
+### NixOS XX.XX platform

doc/src/rabbitmq.md

@@ -18,6 +18,28 @@ We remove the guest user for security reasons.
 Service users can access the rabbitmq account with {command}`sudo -iu rabbitmq`
 to perform administrative tasks with {command}`rabbitmqctl`.
 
+Alternatively, [`rabbitmqadmin-ng`](https://www.rabbitmq.com/docs/management-cli) may be used
+to interact with the HTTP API. It is installed by default with the `rabbitmq` role.
+
+For this to work, a `~/.rabbitmqadmin.conf` is required with a configuration like this:
+
+```toml
+[default]
+hostname = "localhost"
+port = 15672
+username = "myusername"
+password = "mypassword"
+vhost = '/'
+```
+
+For this, you need a user `myusername` in RabbitMQ with the tags
+`administrator` & `management`. Such a user can be created like this:
+
+```
+rabbitmqctl add_user myusername mypassword
+rabbitmqctl set_user_tags myusername management administrator
+```
+
 ## Monitoring
 
 The default monitoring setup checks that the RabbitMQ server is healthy and responding to AMQP connections.

nixos/services/rabbitmq/default.nix

@@ -142,7 +142,7 @@ in {
   config = mkIf cfg.enable {
 
     # This is needed so we will have 'rabbitmqctl' in our PATH
-    environment.systemPackages = [ cfg.package ];
+    environment.systemPackages = [ cfg.package pkgs.rabbitmqadmin-ng ];
     environment.etc."local/rabbitmq/README.txt".text = ''
       RabbitMQ (${cfg.package.version}) is running on this machine.