use a new Session for each lambda invocation

this attempts to work around an issue we see with requests to Opencast
possibly failing when re-using urllib https connections

functions/zoom-uploader.py

@@ -40,20 +40,8 @@
 aws_lambda = boto3.client("lambda")
 sqs = boto3.resource("sqs")
 
-session = requests.Session()
-session.auth = HTTPDigestAuth(OPENCAST_API_USER, OPENCAST_API_PASSWORD)
-session.headers.update(
-    {
-        "X-REQUESTED-AUTH": "Digest",
-        # TODO: it's possible this header is not necessary for the endpoints
-        # being used here. It seems like for Opencast endpoints where the
-        # header *is* necessary the correct value is actually
-        # "X-Opencast-Matterhorn-Authorization"
-        "X-Opencast-Matterhorn-Authentication": "true",
-    }
-)
-
 UPLOAD_OP_TYPES = ["track", "uri-track"]
+SESSION = None
 
 
 class OpencastConnectionError(Exception):
@@ -65,10 +53,12 @@ class InvalidOpencastSeriesId(Exception):
 
 
 def oc_api_request(method, endpoint, **kwargs):
+
     url = urljoin(OPENCAST_BASE_URL, endpoint)
     logger.info({"url": url, "kwargs": kwargs})
+
     try:
-        resp = session.request(method, url, **kwargs)
+        resp = SESSION.request(method, url, **kwargs)
     except requests.RequestException:
         raise OpencastConnectionError
     resp.raise_for_status()
@@ -89,6 +79,16 @@ def handler(event, context):
     else:
         logger.info(f"{len(messages)} upload messages in queue")
 
+    global SESSION
+    SESSION = requests.Session()
+    SESSION.auth = HTTPDigestAuth(OPENCAST_API_USER, OPENCAST_API_PASSWORD)
+    SESSION.headers.update(
+        {
+            "X-REQUESTED-AUTH": "Digest",
+            "X-Opencast-Matterhorn-Authentication": "true",
+        }
+    )
+
     upload_message = messages[0]
     logger.info(
         {
@@ -118,6 +118,7 @@ def handler(event, context):
         else:
             final_status = PipelineStatus.IGNORED
             logger.info("No workflow initiated.")
+
     except Exception as e:
         logger.exception(e)
         final_status = PipelineStatus.UPLOADER_FAILED
@@ -133,6 +134,7 @@ def handler(event, context):
                 final_status,
                 reason=reason,
             )
+        SESSION.close()
 
 
 def minutes_in_pipeline(webhook_received_time):