[emerg]: host not found in upstream - docker

Question

I'm a little confused. I am trying to build a Flask application and am deploying it in a docker image with nginx as the web server. After I run docker-compose up I am able to get the containers into a running state but in the output of the command I get the following: [emerg] 1#1: host not found in upstream "flask:8000" in in /etc/nginx/nginx.conf:12. The odd thing is if I access localhost I'm able to see the application working. I don't know if this is something I need to address, since it's working? Additionally, I'm trying to setup redirects from HTTP to HTTPS, that seems to not work. Below is my docker-compose file and the nginx.conf file, and the docker file I have for the nginx container. Any advice would be helpful.
Docker Compose
version: "3"
services:
app:
build: ./app
container_name: containerize_app_1
command: gunicorn --chdir app/src --bind 0.0.0.0:8000 --workers 2 "server:app"
volumes:
- ./:/var/www
expose:
- 8000
networks:
- MyNetwork
nginx:
build: ./nginx
container_name: containerize_nginx_1
volumes:
- ./nginx/nginx.conf:/etc/nginx/nginx.conf
ports:
- 80:80
depends_on:
- app
networks:
MyNetwork:
aliases:
- flask-app
networks:
MyNetwork:
nginx.conf
user nginx nginx;
worker_processes 2;
error_log /var/log/nginx/error.log;
worker_rlimit_nofile 8192;
events {
worker_connections 4096;
}
http {
upstream flask-app {
server app:8000;
}
server {
listen 80;
server_name localhost;
return 301 https://$host$request_uri;
location / {
proxy_pass http://flask-app;
proxy_set_header Host "localhost";
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_redirect off;
}
}
}
nginx dockerfile
FROM nginx
RUN rm /etc/nginx/conf.d/default.conf
COPY nginx.conf /etc/nginx/nginx.conf
docker-compose up
docker-compose up
containerize_app_1 is up-to-date
containerize_nginx_1 is up-to-date
Attaching to containerize_app_1, containerize_nginx_1
app_1 | [2021-12-14 21:48:01 +0000] [1] [INFO] Starting gunicorn 19.9.0
app_1 | [2021-12-14 21:48:01 +0000] [1] [INFO] Listening at: http://0.0.0.0:8000 (1)
app_1 | [2021-12-14 21:48:01 +0000] [1] [INFO] Using worker: sync
app_1 | [2021-12-14 21:48:01 +0000] [12] [INFO] Booting worker with pid: 12
app_1 | [2021-12-14 21:48:01 +0000] [13] [INFO] Booting worker with pid: 13
app_1 | [2021-12-14 22:21:03 +0000] [1] [CRITICAL] WORKER TIMEOUT (pid:12)
app_1 | [2021-12-14 22:21:03 +0000] [1] [CRITICAL] WORKER TIMEOUT (pid:13)
app_1 | [2021-12-14 22:21:03 +0000] [13] [INFO] Worker exiting (pid: 13)
app_1 | [2021-12-14 22:21:03 +0000] [12] [INFO] Worker exiting (pid: 12)
app_1 | [2021-12-14 22:21:03 +0000] [14] [INFO] Booting worker with pid: 14
app_1 | [2021-12-14 22:21:04 +0000] [15] [INFO] Booting worker with pid: 15
app_1 | [2021-12-14 22:27:44 +0000] [1] [CRITICAL] WORKER TIMEOUT (pid:14)
app_1 | [2021-12-14 22:27:44 +0000] [1] [CRITICAL] WORKER TIMEOUT (pid:15)
app_1 | [2021-12-14 22:27:44 +0000] [14] [INFO] Worker exiting (pid: 14)
app_1 | [2021-12-14 22:27:44 +0000] [15] [INFO] Worker exiting (pid: 15)
app_1 | [2021-12-14 22:27:44 +0000] [16] [INFO] Booting worker with pid: 16
app_1 | [2021-12-14 22:27:45 +0000] [17] [INFO] Booting worker with pid: 17
app_1 | [2021-12-14 22:32:53 +0000] [1] [CRITICAL] WORKER TIMEOUT (pid:16)
app_1 | [2021-12-14 22:32:53 +0000] [1] [CRITICAL] WORKER TIMEOUT (pid:17)
app_1 | [2021-12-14 22:32:53 +0000] [16] [INFO] Worker exiting (pid: 16)
app_1 | [2021-12-14 22:32:53 +0000] [17] [INFO] Worker exiting (pid: 17)
app_1 | [2021-12-14 22:32:53 +0000] [18] [INFO] Booting worker with pid: 18
app_1 | [2021-12-14 22:32:53 +0000] [19] [INFO] Booting worker with pid: 19
app_1 | [2021-12-14 22:42:31 +0000] [1] [CRITICAL] WORKER TIMEOUT (pid:18)
app_1 | [2021-12-14 22:42:31 +0000] [1] [CRITICAL] WORKER TIMEOUT (pid:19)
app_1 | [2021-12-14 22:42:31 +0000] [19] [INFO] Worker exiting (pid: 19)
app_1 | [2021-12-14 22:42:31 +0000] [18] [INFO] Worker exiting (pid: 18)
app_1 | [2021-12-14 22:42:31 +0000] [20] [INFO] Booting worker with pid: 20
app_1 | [2021-12-14 22:42:31 +0000] [21] [INFO] Booting worker with pid: 21
app_1 | [2021-12-14 22:48:26 +0000] [1] [CRITICAL] WORKER TIMEOUT (pid:20)
app_1 | [2021-12-14 22:48:26 +0000] [1] [CRITICAL] WORKER TIMEOUT (pid:21)
app_1 | [2021-12-14 22:48:26 +0000] [21] [INFO] Worker exiting (pid: 21)
app_1 | [2021-12-14 22:48:26 +0000] [20] [INFO] Worker exiting (pid: 20)
app_1 | [2021-12-14 22:48:26 +0000] [22] [INFO] Booting worker with pid: 22
app_1 | [2021-12-14 22:48:26 +0000] [23] [INFO] Booting worker with pid: 23
app_1 | [2021-12-15 00:11:42 +0000] [1] [CRITICAL] WORKER TIMEOUT (pid:22)
app_1 | [2021-12-15 00:11:42 +0000] [1] [CRITICAL] WORKER TIMEOUT (pid:23)
app_1 | [2021-12-15 00:11:42 +0000] [23] [INFO] Worker exiting (pid: 23)
app_1 | [2021-12-15 00:11:42 +0000] [22] [INFO] Worker exiting (pid: 22)
app_1 | [2021-12-15 00:11:42 +0000] [24] [INFO] Booting worker with pid: 24
app_1 | [2021-12-15 00:11:42 +0000] [25] [INFO] Booting worker with pid: 25
app_1 | [2021-12-15 01:55:27 +0000] [1] [CRITICAL] WORKER TIMEOUT (pid:24)
app_1 | [2021-12-15 01:55:27 +0000] [1] [CRITICAL] WORKER TIMEOUT (pid:25)
app_1 | [2021-12-15 01:55:27 +0000] [24] [INFO] Worker exiting (pid: 24)
app_1 | [2021-12-15 01:55:27 +0000] [25] [INFO] Worker exiting (pid: 25)
app_1 | [2021-12-15 01:55:27 +0000] [26] [INFO] Booting worker with pid: 26
app_1 | [2021-12-15 01:55:27 +0000] [27] [INFO] Booting worker with pid: 27
app_1 | [2021-12-15 02:34:31 +0000] [1] [CRITICAL] WORKER TIMEOUT (pid:26)
app_1 | [2021-12-15 02:34:31 +0000] [1] [CRITICAL] WORKER TIMEOUT (pid:27)
app_1 | [2021-12-15 02:34:31 +0000] [27] [INFO] Worker exiting (pid: 27)
app_1 | [2021-12-15 02:34:31 +0000] [26] [INFO] Worker exiting (pid: 26)
app_1 | [2021-12-15 02:34:31 +0000] [28] [INFO] Booting worker with pid: 28
app_1 | [2021-12-15 02:34:31 +0000] [29] [INFO] Booting worker with pid: 29
nginx_1 | /docker-entrypoint.sh: /docker-entrypoint.d/ is not empty, will attempt to perform configuration
nginx_1 | /docker-entrypoint.sh: Looking for shell scripts in /docker-entrypoint.d/
nginx_1 | /docker-entrypoint.sh: Launching /docker-entrypoint.d/10-listen-on-ipv6-by-default.sh
nginx_1 | 10-listen-on-ipv6-by-default.sh: info: /etc/nginx/conf.d/default.conf is not a file or does not exist
nginx_1 | /docker-entrypoint.sh: Launching /docker-entrypoint.d/20-envsubst-on-templates.sh
nginx_1 | /docker-entrypoint.sh: Launching /docker-entrypoint.d/30-tune-worker-processes.sh
nginx_1 | /docker-entrypoint.sh: Configuration complete; ready for start up
nginx_1 | 2021/12/14 23:37:02 [emerg] 1#1: host not found in upstream "flask:8000" in /etc/nginx/nginx.conf:12
nginx_1 | nginx: [emerg] host not found in upstream "flask:8000" in /etc/nginx/nginx.conf:12
nginx_1 | /docker-entrypoint.sh: /docker-entrypoint.d/ is not empty, will attempt to perform configuration
nginx_1 | /docker-entrypoint.sh: Looking for shell scripts in /docker-entrypoint.d/
nginx_1 | /docker-entrypoint.sh: Launching /docker-entrypoint.d/10-listen-on-ipv6-by-default.sh
nginx_1 | 10-listen-on-ipv6-by-default.sh: info: /etc/nginx/conf.d/default.conf is not a file or does not exist
nginx_1 | /docker-entrypoint.sh: Launching /docker-entrypoint.d/20-envsubst-on-templates.sh
nginx_1 | /docker-entrypoint.sh: Launching /docker-entrypoint.d/30-tune-worker-processes.sh
nginx_1 | /docker-entrypoint.sh: Configuration complete; ready for start up
nginx_1 | 172.18.0.1 - - [14/Dec/2021:23:48:17 +0000] "GET / HTTP/1.1" 200 128 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/15.0 Safari/605.1.15"
nginx_1 | 172.18.0.1 - - [15/Dec/2021:02:22:03 +0000] "GET / HTTP/1.1" 200 128 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/15.0 Safari/605.1.15"