fix(fastapi): use metrics in cases where PROMETHEUS_MULTIPROC_DIR is defined

Previously, we restricted this to gunicorn to get it working on aur-dev.
This change makes it usable through any backend, and also no-op if
PROMETHEUS_MULTIPROC_DIR is not defined.

Signed-off-by: Kevin Morris <kevr@0cost.org>

aurweb/routers/html.py

@@ -209,9 +209,7 @@ async def index(request: Request):
 @router.get("/metrics")
 async def metrics(request: Request):
     registry = CollectorRegistry()
-    if os.environ.get("FASTAPI_BACKEND", "") == "gunicorn":  # pragma: no cover
-        # This case only ever happens in production, when we are running
-        # gunicorn. We don't test with gunicorn, so we don't cover this path.
+    if os.environ.get("PROMETHEUS_MULTIPROC_DIR", None):  # pragma: no cover
         multiprocess.MultiProcessCollector(registry)
     data = generate_latest(registry)
     headers = {

docker-compose.yml

@@ -241,6 +241,7 @@ services:
     environment:
       - AUR_CONFIG=conf/config
       - TEST_RECURSION_LIMIT=${TEST_RECURSION_LIMIT}
+      - PROMETHEUS_MULTIPROC_DIR=/tmp_prometheus
     entrypoint: /docker/test-mysql-entrypoint.sh
     command: /docker/scripts/run-pytests.sh clean
     stdin_open: true
@@ -267,6 +268,7 @@ services:
     environment:
       - AUR_CONFIG=conf/config.sqlite
       - TEST_RECURSION_LIMIT=${TEST_RECURSION_LIMIT}
+      - PROMETHEUS_MULTIPROC_DIR=/tmp_prometheus
     entrypoint: /docker/test-sqlite-entrypoint.sh
     command: setup-sqlite.sh run-pytests.sh clean
     stdin_open: true
@@ -289,6 +291,7 @@ services:
     environment:
       - AUR_CONFIG=conf/config
       - TEST_RECURSION_LIMIT=${TEST_RECURSION_LIMIT}
+      - PROMETHEUS_MULTIPROC_DIR=/tmp_prometheus
     entrypoint: /docker/tests-entrypoint.sh
     command: setup-sqlite.sh run-tests.sh
     stdin_open: true

docker/scripts/run-pytests.sh

@@ -22,6 +22,9 @@ while [ $# -ne 0 ]; do
     esac
 done
 
+rm -rf $PROMETHEUS_MULTIPROC_DIR
+mkdir -p $PROMETHEUS_MULTIPROC_DIR
+
 # Initialize the new database; ignore errors.
 python -m aurweb.initdb 2>/dev/null || \
     (echo "Error: aurweb.initdb failed; already initialized?" && /bin/true)