check_swarm.py returns "Node not in a swarm" for non-manager nodes in a swarm

[esabol]

Running check_swarm.py --swarm works on manager nodes, but it fails on non-manager nodes with the incorrect message "Node not in a swarm". If you promote the non-manager node to a manager, it reports OK. If you demote some other node from being a manager, that node now fails with the aforementioned message.

I think this is due to a misunderstanding of the swarm API. It's looking for the wrong thing in the JSON, imho. (Not every node in a swarm should be a manager once you get more than 3 or 5 nodes.)

[esabol]

I made the following modifications to use the /v1.41/info Docker API endpoint and then to check if .Swarm.LocalNodeState == active:

--- /path/to/check_swarm.orig     2025-07-14 17:31:09.961650000 -0400
+++ /path/to/check_swarm          2025-08-13 18:09:17.220752000 -0400
@@ -36,6 +36,7 @@
 WARNING_RC = 1
 CRITICAL_RC = 2
 UNKNOWN_RC = 3
+API_VERSION = '1.41'
 
 HTTP_GOOD_CODES = range(200, 299)
 
@@ -109,6 +110,10 @@
     return tasks
 
 
+def get_info():
+    return get_url(daemon + f'/v{API_VERSION}/info')
+
+
 def get_nodes():
     return get_url(daemon + '/nodes')
 
@@ -169,10 +174,22 @@
 
 # Checks
 #############################################################################################
 def check_swarm():
-    status = get_swarm_status()
-    process_url_status(status, ok_msg='Node is in a swarm',
-                       critical_msg='Node is not in a swarm', unknown_msg='Error accessing swarm info')
+    info, status = get_info()
+    if 'Swarm' in info and info['Swarm']['LocalNodeState'] == 'active':
+        ok('Node is in a swarm.')
+    else:
+        critical('Node is not in a swarm.');

Let me know what you think of this. Would you like me to submit a PR?