Merge ~vtapia/maas:lp1927941-27 into maas:2.7

[Victor Tapia]

Reuse metric structures for Prometheus

Backport of 2ad24e0

[MAAS Lander (maas-lander)]

UNIT TESTS
-b lp1927941-27 lp:~vtapia/maas/+git/maas into -b 2.7 lp:~maas-committers/maas

STATUS: FAILED
LOG: http://maas-ci.internal:8080/job/maas/job/branch-tester/10204/console
COMMIT: c6fdbd45daa4a020dc4041ce7ea312a562b89c5b

review: Needs Fixing

[MAAS Lander (maas-lander)]

UNIT TESTS
-b lp1927941-27 lp:~vtapia/maas/+git/maas into -b 2.7 lp:~maas-committers/maas

STATUS: FAILED
LOG: http://maas-ci.internal:8080/job/maas/job/branch-tester/10239/console
COMMIT: 138ffb82ee7e14dd1bb21b9d10206024b435bcf2

review: Needs Fixing

[Victor Tapia (vtapia)]

I haven't been able to reproduce the locale issue ("RuntimeError: Click will abort further execution because Python was configured to use ASCII as encoding for the environment") using my local bionic builder, even after setting the default locale to C:

$ env | egrep 'LANG|LC_'
LANG=C

$ sudo -E -H -u ubuntu -- python -c 'import locale; import codecs; print(codecs.lookup(locale.getpreferredencoding()).name)'
ascii

This same issue happens for both bionic releases (2.7 and 2.8) and according to https://click.palletsprojects.com/en/7.x/python3/:

"In Python 3.7 and later you will no longer get a RuntimeError in many cases thanks to PEP 538 and PEP 540, which changed the default assumption in unconfigured environments."

Bionic ships 3.6, which might explain why this happens only on its releases and not on Focal's (Python 3.8).

Could this be a builder issue?

[Adam Collard (adam-collard)]

review: Approve

[Adam Collard (adam-collard)]

jenkins: !test

[MAAS Lander (maas-lander)]

UNIT TESTS
-b lp1927941-27 lp:~vtapia/maas/+git/maas into -b 2.7 lp:~maas-committers/maas

STATUS: FAILED
LOG: http://maas-ci.internal:8080/job/maas/job/branch-tester/10271/console
COMMIT: 138ffb82ee7e14dd1bb21b9d10206024b435bcf2

review: Needs Fixing

[Adam Collard (adam-collard)]

jenkins: !test

[MAAS Lander (maas-lander)]

UNIT TESTS
-b lp1927941-27 lp:~vtapia/maas/+git/maas into -b 2.7 lp:~maas-committers/maas

STATUS: SUCCESS
COMMIT: 138ffb82ee7e14dd1bb21b9d10206024b435bcf2

review: Approve

diff --git a/src/maasserver/prometheus/stats.py b/src/maasserver/prometheus/stats.py
index 3d5a5ea..fd4fadf 100644
--- a/src/maasserver/prometheus/stats.py
+++ b/src/maasserver/prometheus/stats.py
@@ -115,6 +115,8 @@ STATS_DEFINITIONS = [
     ),
 ]
 
+_METRICS = {}
+
 
 def prometheus_stats_handler(request):
     configs = Config.objects.get_configs(["prometheus_enabled", "uuid"])
@@ -122,14 +124,17 @@ def prometheus_stats_handler(request):
     if not have_prometheus:
         return HttpResponseNotFound()
 
-    metrics = create_metrics(
-        STATS_DEFINITIONS,
-        extra_labels={"maas_id": configs["uuid"]},
-        update_handlers=[update_prometheus_stats],
-        registry=prom_cli.CollectorRegistry(),
-    )
+    global _METRICS
+    if not _METRICS:
+        _METRICS = create_metrics(
+            STATS_DEFINITIONS,
+            extra_labels={"maas_id": configs["uuid"]},
+            update_handlers=[update_prometheus_stats],
+            registry=prom_cli.CollectorRegistry(),
+        )
+
     return HttpResponse(
-        content=metrics.generate_latest(), content_type="text/plain"
+        content=_METRICS.generate_latest(), content_type="text/plain"
     )