services: Add epmd-service-type.

Add Erlang Port Mapper Daemon (epmd) service.
Run the service on localhost by default.

* gnu/services/high-availability.scm (<epmd-configuration>): New record.
  (epmd-service-type): New variable.
* gnu/tests/high-availability.scm (run-epmd-test): New procedure.
  (%epmd-os, %tests-epmd): New variables.
* doc/gnu.texi (High Availability Services): Document it.

Merges: https://codeberg.org/guix/guix/pulls/9607
References: https://www.rabbitmq.com/blog/2024/12/18/epmd-public-exposure
References: https://erlef.org/blog/eef/epmd-public-exposure
Signed-off-by: Nguyễn Gia Phong <cnx@loang.net>

1 files changed, 80 insertions, 1 deletions

diff --git a/gnu/tests/high-availability.scm b/gnu/tests/high-availability.scm
index 6eb13d1a068..faa657bfc3c 100644
--- a/gnu/tests/high-availability.scm
+++ b/gnu/tests/high-availability.scm
@@ -19,6 +19,7 @@
 
 (define-module (gnu tests high-availability)
   #:use-module (gnu tests)
+  #:use-module (gnu packages erlang)
   #:use-module (gnu packages high-availability)
   #:use-module (gnu system)
   #:use-module (gnu system file-systems)
@@ -29,7 +30,85 @@
   #:use-module (gnu services networking)
   #:use-module (guix gexp)
   #:use-module (guix store)
-  #:export (%test-rabbitmq))
+  #:export (%test-epmd
+            %test-rabbitmq))
+
+;;;
+;;; Erlang Port Mapper Daemon (epmd) service.
+;;;
+(define %epmd-os
+  (simple-operating-system
+    (service epmd-service-type
+             (epmd-configuration (port 14369)))))
+
+(define* (run-epmd-test #:key (epmd-port 14369))
+  "Run tests in %EPMD-OS, forwarding PORT."
+  (define os
+    (marionette-operating-system
+      %epmd-os
+      #:imported-modules '((gnu services herd)
+                           (guix combinators))))
+
+  (define forwarded-port 14369)
+
+  (define vm
+    (virtual-machine
+     (operating-system os)
+     (memory-size 512)
+     (port-forwardings `((,epmd-port . ,forwarded-port)))))
+
+  (define test
+    (with-imported-modules '((gnu build marionette))
+      #~(begin
+          (use-modules (srfi srfi-64)
+                       (gnu build marionette)
+                       (ice-9 rdelim))
+
+          (define marionette
+            (make-marionette (list #$vm)))
+
+          (mkdir #$output)
+          (chdir #$output)
+
+          (test-runner-current (system-test-runner #$output))
+          (test-begin "epmd")
+
+          ;; Wait for epmd to be up and running.
+          (test-assert "service running"
+            (marionette-eval
+             '(begin
+                (use-modules (gnu services herd))
+                (match (start-service 'epmd)
+                  (#f #f)
+                  (('service response-parts ...)
+                   (match (assq-ref response-parts 'running)
+                     ((#t) #t)
+                     ((pid) pid)))))
+             marionette))
+
+          (test-assert "epmd port ready"
+            (wait-for-tcp-port #$forwarded-port marionette))
+
+          (test-assert "epmd connection is successful"
+            (marionette-eval
+             '(begin
+                (use-modules (guix build utils))
+
+                (current-output-port (open-file "/dev/console" "w0"))
+                (invoke #$(file-append erlang "/bin/epmd")
+                        "-port"
+                        "14369"
+                        "-names"))
+             marionette))
+          (test-end))))
+
+  (gexp->derivation "epmd-test" test))
+
+(define %test-epmd
+  (system-test
+   (name "epmd")
+   (description "Connect to a running epmd service.")
+   (value (run-epmd-test))))
 
 (define %rabbitmq-config-file
   (plain-file "rabbitmq.conf" "