Merge ~adam-collard/maas:prometheus-gateway-ip-cache into maas:master

[Adam Collard]

Don't get_machine_default_gateway every time we collect metrics

Partial fix for LP:1978225

[Jack Lloyd-Walters (lloydwaltersj)]

+1

review: Approve

[MAAS Lander (maas-lander)]

LANDING
-b prometheus-gateway-ip-cache lp:~adam-collard/maas/+git/maas into -b master lp:~maas-committers/maas

STATUS: FAILED BUILD
LOG: http://maas-ci.internal:8080/job/maas-tester/207/consoleText

[Jack Lloyd-Walters (lloydwaltersj)]

I'm going to start another build, because that one hit timeout, rather than any code issue

[Jack Lloyd-Walters (lloydwaltersj)]

jenkins: !test

[MAAS Lander (maas-lander)]

UNIT TESTS
-b prometheus-gateway-ip-cache lp:~adam-collard/maas/+git/maas into -b master lp:~maas-committers/maas

STATUS: SUCCESS
COMMIT: 1fa6d3820463572243c6ee890f0d7beb338dc626

review: Approve

diff --git a/src/provisioningserver/prometheus/metrics.py b/src/provisioningserver/prometheus/metrics.py
index 68719d4..8f117ff 100644
--- a/src/provisioningserver/prometheus/metrics.py
+++ b/src/provisioningserver/prometheus/metrics.py
@@ -134,7 +134,7 @@ def set_global_labels(**labels):
 PROMETHEUS_METRICS = create_metrics(
     METRICS_DEFINITIONS,
     extra_labels={
-        "host": get_machine_default_gateway_ip,
+        "host": get_machine_default_gateway_ip(),
         "maas_id": lambda: GLOBAL_LABELS["maas_uuid"],
     },
     update_handlers=[update_cpu_metrics, update_memory_metrics],