Keep the path prefix of Alertmanager and Prometheus URLs

promgen/prometheus.py

@@ -6,7 +6,7 @@
 import logging
 import subprocess
 import tempfile
-from urllib.parse import parse_qs, urljoin, urlparse
+from urllib.parse import parse_qs, urlparse
 
 import yaml
 from dateutil import parser
@@ -335,7 +335,7 @@ def silence(*, labels, duration=None, **kwargs):
         ]
 
     logger.debug("Sending silence for %s", kwargs)
-    url = urljoin(util.setting("alertmanager:url"), "/api/v2/silences")
+    url = util.join_url(util.setting("alertmanager:url"), "/api/v2/silences")
     response = util.post(url, json=kwargs)
     response.raise_for_status()
     return response

promgen/proxy.py

@@ -5,7 +5,6 @@
 import json
 import logging
 from http import HTTPStatus
-from urllib.parse import urljoin
 
 import requests
 from django.http import HttpResponse, JsonResponse
@@ -47,7 +46,7 @@ def proxy(self, request):
                 futures.append(
                     executor.submit(
                         util.get,
-                        urljoin(shard.url, request.get_full_path_info()),
+                        util.join_url(shard.url, request.get_full_path_info()),
                         headers=headers,
                     )
                 )
@@ -160,7 +159,7 @@ def get(self, request):
 class ProxyAlerts(View):
     def get(self, request):
         try:
-            url = urljoin(util.setting("alertmanager:url"), "/api/v2/alerts")
+            url = util.join_url(util.setting("alertmanager:url"), "/api/v2/alerts")
             response = util.get(url)
         except requests.exceptions.ConnectionError:
             logger.error("Error connecting to %s", url)
@@ -270,7 +269,7 @@ def get_queryset_for_matcher(matcher, klass):
 class ProxySilences(View):
     def get(self, request):
         try:
-            url = urljoin(util.setting("alertmanager:url"), "/api/v2/silences")
+            url = util.join_url(util.setting("alertmanager:url"), "/api/v2/silences")
             response = util.get(url, params={"silenced": False})
         except requests.exceptions.ConnectionError:
             logger.error("Error connecting to %s", url)
@@ -491,7 +490,7 @@ def post(self, request, *args, **kwargs):
 
 class ProxyDeleteSilence(View):
     def delete(self, request, silence_id):
-        url = urljoin(util.setting("alertmanager:url"), f"/api/v2/silence/{silence_id}")
+        url = util.join_url(util.setting("alertmanager:url"), f"/api/v2/silence/{silence_id}")
         # First, check if the silence exists
         response = util.get(url)
         if response.status_code != 200:

promgen/tasks.py

@@ -5,7 +5,6 @@
 import os
 import socket
 from datetime import datetime
-from urllib.parse import urljoin
 
 from atomicwrites import atomic_write
 from billiard.exceptions import SoftTimeLimitExceeded
@@ -184,15 +183,15 @@ def send_notification(*args, alert_pk, **kwargs):
 def reload_prometheus():
     from promgen import signals
 
-    target = urljoin(util.setting("prometheus:url"), "/-/reload")
+    target = util.join_url(util.setting("prometheus:url"), "/-/reload")
     response = util.post(target)
     response.raise_for_status()
     signals.post_reload.send(response)
 
 
 @shared_task(base=BaseTaskWithRetry)
 def clear_tombstones():
-    target = urljoin(util.setting("prometheus:url"), "/api/v1/admin/tsdb/clean_tombstones")
+    target = util.join_url(util.setting("prometheus:url"), "/api/v1/admin/tsdb/clean_tombstones")
     response = util.post(target)
     response.raise_for_status()
 

promgen/tests/test_util.py

@@ -23,3 +23,28 @@ def test_categorize_error(self):
         for error, expected in cases:
             with self.subTest(error=type(error).__name__, expected=expected):
                 self.assertEqual(util.categorize_error(error), expected)
+
+    def test_join_url(self):
+        cases = [
+            ("http://prometheus:9090", "/-/reload", "http://prometheus:9090/-/reload"),
+            ("http://prometheus:9090/", "/-/reload", "http://prometheus:9090/-/reload"),
+            (
+                "http://example.com/prometheus",
+                "/-/reload",
+                "http://example.com/prometheus/-/reload",
+            ),
+            (
+                "http://example.com/prometheus/",
+                "/api/v1/query?query=up",
+                "http://example.com/prometheus/api/v1/query?query=up",
+            ),
+            (
+                "http://example.com/alertmanager/",
+                "api/v2/silences",
+                "http://example.com/alertmanager/api/v2/silences",
+            ),
+        ]
+
+        for base, path, expected in cases:
+            with self.subTest(base=base, path=path):
+                self.assertEqual(util.join_url(base, path), expected)

promgen/util.py

@@ -60,6 +60,13 @@ def scrape(url, params=None, **kwargs):
     return requests.get(url, params=params, **kwargs)
 
 
+def join_url(base, path):
+    """
+    Append a path to a base URL, keeping any path prefix of the base URL
+    """
+    return f"{base.removesuffix('/')}/{path.removeprefix('/')}"
+
+
 def setting(key, default=None, domain=None):
     """
     Settings helper based on saltstack's query