Merge ~cjwatson/launchpad:charm-wsgi-worker-max-requests into launchpad:master

[Colin Watson]

charm: Reduce max_requests and make it configurable

Our Juju-deployed appservers currently have a little less memory than our bare-metal ones, so memory leaks cause a problem slightly earlier. Reduce the Gunicorn `max_requests` setting to cope with this, and make it configurable using `juju config`.

[Nick Moffitt (nick-moffitt)]

I applied this temporarily to one appserver unit, and can confirm its effectiveness.

review: Approve

[Guruprasad (lgp171188)]

LGTM 👍🏼

review: Approve

diff --git a/charm/launchpad-appserver/config.yaml b/charm/launchpad-appserver/config.yaml
index 93586e2..f016031 100644
--- a/charm/launchpad-appserver/config.yaml
+++ b/charm/launchpad-appserver/config.yaml
@@ -47,6 +47,12 @@ options:
     type: int
     description: Port for the main application server.
     default: 8085
+  wsgi_worker_max_requests:
+    type: int
+    description: >
+      Restart WSGI worker processes after handling this many requests.  This
+      works around memory leaks.
+    default: 1000
   wsgi_workers:
     type: int
     default: 0
diff --git a/charm/launchpad-appserver/templates/gunicorn.conf.py.j2 b/charm/launchpad-appserver/templates/gunicorn.conf.py.j2
index 09d8866..19a2ad1 100644
--- a/charm/launchpad-appserver/templates/gunicorn.conf.py.j2
+++ b/charm/launchpad-appserver/templates/gunicorn.conf.py.j2
@@ -3,7 +3,7 @@ workers = {{ wsgi_workers }}
 # Incompatible with `reload = True`, but that's fine for a Juju deployment.
 preload_app = True
 # This is set relatively low to work around memory leaks on Python 3.
-max_requests = 2000
+max_requests = {{ wsgi_worker_max_requests }}
 log_level = "DEBUG"
 # Must be higher than the highest hard_timeout feature rule.
 timeout = 65