How To Fix Nginx "Host Not Found In Upstream" Error In Docker?

Using depends_on in docker-compose.yml

The depends_on directive in docker-compose.yml helps manage the startup order of containers. It tells Docker to start certain containers before others. This can help prevent the "Host Not Found In Upstream" error by making sure the required services are running before Nginx starts.

To implement depends_on in your docker-compose.yml file, add it under the Nginx service and list the services it should wait for:

version: '3'
services:
  nginx:
    image: nginx
    depends_on:
      - php
    # Other Nginx configuration...

  php:
    image: php:fpm
    # PHP configuration...

Updating the Nginx configuration

Check the fastcgi_pass directive in your Nginx configuration. Make sure it uses the correct service name as defined in your docker-compose.yml file. If your PHP service is named "php" in docker-compose.yml, your fastcgi_pass should look like this:

fastcgi_pass php:9000;

Also, check that the service names in your Nginx configuration match those in your docker-compose.yml file. Mismatched names can cause the "Host Not Found In Upstream" error.

Implementing wait-for-it scripts

Wait-for-it scripts are shell scripts that pause the startup of a container until a specific service is ready. These scripts can help prevent the "Host Not Found In Upstream" error by making sure Nginx only starts after the required services are fully operational.

To use a wait-for-it script in your Docker setup:

1. Add the script to your project directory.
2. Update your Dockerfile to include the script.
3. Change the command in your docker-compose.yml to use the wait-for-it script:

nginx:
  image: nginx
  depends_on:
    - php
  command: ["./wait-for-it.sh", "php:9000", "--", "nginx", "-g", "daemon off;"]
  # Other Nginx configuration...

This approach adds protection against timing issues that can cause the "Host Not Found In Upstream" error.

#!/bin/bash
set -e

host="$1"
shift
cmd="$@"

until nc -z "$host" 9000; do
  >&2 echo "PHP-FPM is unavailable - sleeping"
  sleep 1
done

>&2 echo "PHP-FPM is up - executing command"
exec $cmd

nginx:
  image: nginx
  depends_on:
    - php
  command: ["./wait-for-php.sh", "php", "nginx", "-g", "daemon off;"]
  # Other Nginx configuration...

Using Docker networks

Creating custom Docker networks can help fix the "Host Not Found In Upstream" error. Custom networks allow containers to communicate using their service names as hostnames.

To create a custom network:

1. Define the network in your docker-compose.yml file:

networks:
  myapp_network:
    driver: bridge

2. Connect your services to this network:

services:
  nginx:
    image: nginx
    networks:
      - myapp_network

  php:
    image: php:fpm
    networks:
      - myapp_network

By using a custom network, you improve container communication and reduce hostname resolution issues.

networks:
  frontend:
    driver: bridge
  backend:
    driver: bridge

services:
  nginx:
    networks:
      - frontend
  php:
    networks:
      - frontend
      - backend
  database:
    networks:
      - backend

Implementing healthchecks

Healthchecks in docker-compose.yml can prevent the "Host Not Found In Upstream" error by making sure a service is ready before other services that depend on it start.

To add healthchecks:

1. Include a healthcheck in your docker-compose.yml for the PHP service:

services:
  php:
    image: php:fpm
    healthcheck:
      test: ["CMD", "php-fpm", "-t"]
      interval: 10s
      timeout: 5s
      retries: 3

2. Update the Nginx service to depend on the PHP service's health:

services:
  nginx:
    image: nginx
    depends_on:
      php:
        condition: service_healthy

This setup makes sure Nginx only starts after the PHP service is ready to accept connections, reducing the chance of the "Host Not Found In Upstream" error.