Applications are not properly loaded when using uwsgi

[roock]

When running iris in combination with uwsgi (e.g with the container image), the applications are not properly loaded at startup, leading to 401 errrors when using the webhooks api. Once the applications are fully loaded (e.g. by open iris ui with a web browser), the authentication error goes away without modifying the api call.

Steps to reproduce:

• clone the master branch of the repo
• docker-compose build && docker-compose up -d
• Try to post alertmanager data on the webhook api
  • curl -v -X POST -d @prom-alert.json 'http://localhost:16649/v0/webhooks/alertmanager?application=oncall&key=magic'
  • Will return HTTP/401: {"title":"Authentication failure","description":"Application not found"}
• Open Iris UI in a browser and login: http://localhost:16649 with demo/any password
  • or call the application api endpoint: curl -v http://localhost:16649/v0/applications
• Try again the post the same alertmanager data on the api webhook again
  • curl -v -X POST -d @prom-alert.json 'http://localhost:16649/v0/webhooks/alertmanager?application=oncall&key=magic'
  • The incident is properly created and return HTTP/1.1 201 Created

Some additional logging information:
I've modified https://github.com/linkedin/iris/blob/master/src/iris/cache.py#L52 to print when the applications are loaded.

uwsgi error log:

[2022-06-13 13:13:38 +0000] [10] [INFO] iris.cache Loaded applications: Autoalerts, test-app, iris, oncall
[2022-06-13 13:13:38 +0000] [20] [INFO] iris.cache Loaded applications: Autoalerts, test-app, iris, oncall

uwsgi access log:

13/Jun/2022:13:11:54 +0000 [401] POST /v0/webhooks/alertmanager?application=oncall&key=magic 172.25.0.1 [curl/7.83.1] RT:0 REF:- SZ:248 HTTP/1.1
13/Jun/2022:13:11:57 +0000 [401] POST /v0/webhooks/alertmanager?application=oncall&key=magic 172.25.0.1 [curl/7.83.1] RT:0 REF:- SZ:248 HTTP/1.1
13/Jun/2022:13:13:38 +0000 [302] GET / 172.25.0.1 [Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:101.0) Gecko/20100101 Firefox/101.0] RT:36 REF:- SZ:583 HTTP/1.1
13/Jun/2022:13:13:38 +0000 [200] GET /v0/applications 127.0.0.1 [python-requests/2.28.0] RT:42 REF:- SZ:3668 HTTP/1.1
13/Jun/2022:13:13:38 +0000 [200] GET /incidents 172.25.0.1 [Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:101.0) Gecko/20100101 Firefox/101.0] RT:1729 REF:- SZ:15859 HTTP/1.1
13/Jun/2022:13:14:00 +0000 [201] POST /v0/webhooks/alertmanager?application=oncall&key=magic 172.25.0.1 [curl/7.83.1] RT:24 REF:- SZ:195 HTTP/1.1

This looks like the application cache is not properly populated on startup of the application.

I wasn't able to reproduce the issue with a local setup with gunicorn.

Used Sample Data

{
  "version": "4",
  "groupKey": "{}:{alertname=\"high_memory_load\"}",
  "status": "firing",
  "receiver": "teams_proxy",
  "groupLabels": {
      "alertname": "high_memory_load",
      "iris_plan": "Oncall test"
 },
  "commonLabels": {
      "alertname": "high_memory_load",
      "monitor": "master",
      "severity": "warning"
  },
  "commonAnnotations": {
      "summary": "Server High Memory usage"
  },
  "externalURL": "http://docker.for.mac.host.internal:9093",
  "alerts": [
      {
          "labels": {
              "alertname": "high_memory_load",
              "instance": "10.80.40.11:9100",
              "job": "docker_nodes",
              "monitor": "master",
              "severity": "warning"
          },
          "annotations": {
              "description": "10.80.40.11 reported high memory usage with 23.28%.",
              "summary": "Server High Memory usage"
          },
          "startsAt": "2018-03-07T06:33:21.873077559-05:00",
          "endsAt": "0001-01-01T00:00:00Z"
      }
  ]
}