Merge ~cmars/prometheus-charm:nrpe_check_fix into prometheus-charm:master

[Casey Marshall]

Use external path for nrpe check_http plugin.

Fixes the 404 warning state that prometheus is in w/nagios
when the external_url config option is set; commonly used with url
rewriting in frontend like haproxy.

Use external path for nrpe check_http plugin.

Fixes the 404 warning state that prometheus is in w/nagios
when the external_url config option is set; commonly used with url
rewriting in frontend like haproxy.

[🤖 Canonical IS Merge Bot (canonical-is-mergebot)]

This merge proposal is being monitored by mergebot. Change the status to Approved to merge.

[Domas Monkus (tasdomas)]

review: Approve

[Thomas Cuthbert (tcuthbert)]

comments inline.

review: Needs Fixing

[Casey Marshall (cmars)]

Comment is unclear to me, please advise.

[Paul Gear (paulgear)]

LGTM; in the case where external_url is something like "https://my.special.site:8443", this results in "//graph", but that's only cosmetic.

review: Approve

[🤖 Canonical IS Merge Bot (canonical-is-mergebot)]

Change successfully merged at revision ed0f47541b373f6ec506349766dfbd81708905c9

diff --git a/reactive/prometheus.py b/reactive/prometheus.py
index 669db9c..23c9bab 100644
--- a/reactive/prometheus.py
+++ b/reactive/prometheus.py
@@ -648,9 +648,17 @@ def update_nrpe_config(svc):
     hostname = nrpe.get_nagios_hostname()
     nrpe_setup = nrpe.NRPE(hostname=hostname)
     port = unitdata.kv().get('prometheus.port', 9090)
+
+    config = hookenv.config()
+    graph_path = "/graph"
+    external_url = config.get("external_url", "")
+    if external_url:
+        ext_url = urlparse(external_url)
+        graph_path = '/{}/graph'.format(ext_url.path.strip('/'))
+
     nrpe_setup.add_check('prometheus_http',
                          'Prometheus HTTP check',
-                         'check_http -I 127.0.0.1 -p {} -u /graph'.format(port)
+                         'check_http -I 127.0.0.1 -p {} -u {}'.format(port, graph_path)
                          )
     nrpe_setup.write()