Troubleshooting/FAQ

Table of Contents

• Troubleshooting/FAQ
  • General
    • docker-compose config
    • docker-compose logs
    • docker-compose exec
  • Known issues
    • 1. Network pmd-reverse-proxy-net declared as external, but could not be found.
    • 2.nginx fails to start with nginx: [emerg] host not found in upstream

General

In general various docker-compose commands exist that help you troubleshoot issues you might encounter

docker-compose config

provides a summary of the configuration including all the environment variables specified in .env and other environment files. It also provides feedback if the current configuration has errors

docker-compose logs

usually provides stderr and stdout of a container that can be used to troubleshoot various issues. You can append the servicename to see only the logs of a specific service use the --tail option to limit the output to the last n lines or add -f to follow the output of the container on the terminal.

Examples:

# list the last 100 lines of the nginx service and follow the output
docker-compose logs --tail 100 -f nginx

docker-compose exec

you can get a shell inside a running container with docker-compose exec Examples:

# get a shell inside the nginx container
docker-compose exec nginx sh

# get a bash shell in a container that uses an entrypoint
docker-compose exec --entrypoint=bash app

Known issues

1. Network pmd-reverse-proxy-net declared as external, but could not be found.

This error is typically encountered when the reverse proxy is not running or has an incorrect network name. Make sure you started the reverse proxy by changing into the base directory and issuing docker-compose ps. Furthermore verify that the network name is correct by listing the existing networks using docker network ls and checking whether the network of the reverse proxy exists under a different name.

If you prefer to start the service before configuring the reverse proxy, you can create the network manually as specified in the error message with: docker network create pmd-reverse-proxy-net

2.nginx fails to start with nginx: [emerg] host not found in upstream

This error is typically encountered if you add an nginx configuration with a proxy_pass directive to a service that is either not running or not connected to the nginx network, make sure your app configuration has the network specified as follows:

services:
  app:
    networks:
      - proxy-net

 networks:
  proxy-net:
    name: pmd-reverse-proxy-net
    external: true

also make sure the service is running using docker-compose ps and if not bring it up using docker-compose up -d. Once the service is running go back to the base dir of the reverse proxy and restart nginx using docker-compose restart nginx.