Trouble scaling docker container

Question

I have a dockerized flask app which has the following structure

code_docker
├── docker-compose.yml
├── micr
│   ├── app.py
│   ├── Dockerfile
│   ├── requirements.txt
│   └── templates
│       └── index.html
├── nginx
│   ├── Dockerfile
│   └── nginx.conf
└── README.md

I am using nginx as a load balancer, The code inside docker-compose.yml and nginx.conf are mentioned below

docker-compose.yml

version: '3'

services:

  nginx:
    container_name: nginx
    build: ./nginx
    restart: always
    deploy:
      restart_policy:
        condition: on-failure
    ports:
      - "8540:8540"
    depends_on:
      - micr

  micr:
    build: ./micr
    restart: always 
    deploy: 
      resources:
        limits:
          cpus: '0.50' # 50% of available processing time (CPU)
          memory: 50M  # 50M of memory
        reservations:
          cpus: '0.25'
          memory: 20M
      restart_policy:
        condition: on-failure   
    expose:
      - "8530"
    command: gunicorn -w 1 -b :8530 app:app

nginx.conf

user nginx;

worker_processes 4;

events {
    worker_connections 1024;
}

http {
    keepalive_timeout 15;

    server {
        listen 8540;
        server_name localhost;

        location / {
            proxy_pass http://localhost:8530;
            #proxy_redirect off;
            proxy_set_header Host $host;
            proxy_set_header X-Real-IP $remote_addr;
            proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
            proxy_set_header X-Forward-Host $server_name;
        }
    }
}

I can issue the below command to scale the container without any problem as can be seen from the message

docker-compose up --scale micr=4

But when I try to access them I get this error

@tripleee `http://localhost:8530/` or `http://0.0.0.0:8530/` — Atinesh, Feb 13 '19 at 10:09

score 1 · Accepted Answer · answered Feb 13 '19 at 10:19

1

You need to create a network for Nginx and proxied containers. For details see this.

services:
  nginx:
    networks:
      - proxy
    ...

  micr:
    networks:
      - proxy
    ...

networks:
  proxy:

You need to use service names as container host addresses to archive communication between containers. So set proxy_pass to http://micr:8530
You should set docker embedded dns to nginx resolver to achieve ability to recreate containers without having to restart nginx container. See this for details

answered Feb 13 '19 at 10:19

Artemij Rodionov

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You are the saviour – Atinesh Feb 13 '19 at 11:14
1

(Docker Compose will automatically create a network for you and you don't need to make one explicitly; but the advice to use the container name as a hostname is right on.) – David Maze Feb 13 '19 at 11:35

Trouble scaling docker container

1 Answers1