Kutt Application Returns ERR_EMPTY_RESPONSE When Accessed via Traefik

[angeloluidens]

Description

I am running a Dockerized Kutt application managed via Portainer and served through Traefik in a Docker Swarm setup. The Kutt application is accessible internally (e.g., via curl from within the container), but when accessed externally via the domain short.link', it returns an ERR_EMPTY_RESPONSEerror. The Traefik logs show no errors, and the Kutt application logs indicate that the service is running and listening on port3000`.

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Steps to Reproduce

1. Deploy the Kutt application using the provided Docker Compose script.
2. Access the application via the configured domain (short.link).
3. Observe the ERR_EMPTY_RESPONSE error in the browser.

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Expected Behavior

The Kutt application should be accessible via the configured domain (short.link) and return the expected web interface.

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Actual Behavior

The browser displays the following error:

This page isn’t working right now
short.link didn’t send any data.
ERR_EMPTY_RESPONSE

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Environment

• Kutt Version: kutt/kutt:latest (Docker image)
• Docker Version: 20.10.12
• Docker Swarm: Single-node setup
• Traefik Version: v2.10
• Portainer Version: 2.11.1
• Operating System: Debian 12.5

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Configuration

Docker Compose Script

version: '3.7'

services:
  kutt:
    image: kutt/kutt:latest
    depends_on:
      - mdb
      - redis
    environment:
      - SITE_NAME=MainDomain.Net
      - DEFAULT_DOMAIN=short.link
      - LINK_LENGTH=7
      - DISALLOW_ANONYMOUS_LINKS=true
      - DB_CLIENT=pg
      - DB_HOST=db
      - DB_PORT=5432
      - DB_NAME=kutt
      - DB_USER=user
      - DB_PASSWORD=password
      - JWT_SECRET="###########################################################"
    networks:
      - stack_proxy
      - privatenet
    deploy:
      mode: replicated
      replicas: 1
      update_config:
        order: start-first
      rollback_config:
        order: start-first
      labels:
        - "traefik.enable=true"
        - "traefik.docker.network=sgp_proxy"
        - "traefik.http.routers.kutt.rule=Host(`short.link`)"
        - "traefik.http.services.kutt.loadbalancer.server.port=3000"

networks:
  stack_proxy:
    external: true
  privatenet:
    internal: true

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Troubleshooting Steps Taken

1. Verified Network Connectivity:

   • Confirmed that the Traefik container can ping and access the Kutt container on port 3000.
   • Tested connectivity using curl from the Traefik container:

     curl -vI http://10.0.4.15:3000

     The Kutt application responds correctly internally.

2. Checked Kutt Logs:

   • The Kutt logs show that the application is running and listening on port 3000:

     > Ready on http://localhost:3000
     

   • No errors or crashes are reported in the logs.

3. Verified Traefik Configuration:

   • Traefik is correctly routing traffic to the Kutt container.
   • The Traefik dashboard shows that the kutt service is registered and healthy.

4. Tested Database Connectivity:

   • Verified that the Kutt application can connect to the PostgreSQL database (db) and Redis.
   • Tested the database connection from another container:

     psql -h db -U user -d kutt
     redis-cli -h redis

5. Simplified Configuration:

   • Removed all middleware and simplified the Traefik configuration to the bare minimum.
   • Temporarily disabled HTTPS and tested HTTP routing.

6. Checked for Port Conflicts:

   • Confirmed that no other service is using port 3000.

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Current State

• The Kutt application is running and listening on port 3000.
• Traefik is correctly routing traffic to the Kutt container.
• The application is accessible internally but returns an ERR_EMPTY_RESPONSE error when accessed externally via the domain short.link.

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Additional Information

• Traefik Logs:

  time="2025-03-04T01:16:55Z" level=info msg="Configuration loaded from flags."
  

  No errors are reported in the Traefik logs.

• Kutt Logs:

  > [email protected] migrate
  > knex migrate:latest
  Already up to date
  npm notice
  npm notice New major version of npm available! 10.9.2 -> 11.1.0
  npm notice Changelog: https://github.com/npm/cli/releases/tag/v11.1.0
  npm notice To update run: npm install -g [email protected]
  npm notice
  > [email protected] start
  > node server/server.js --production
  > Ready on http://localhost:3000
  

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Request for Assistance

I would appreciate any guidance on resolving this issue. Specifically:

1. Are there any known issues with running Kutt behind Traefik?
2. Are there additional logs or debugging steps I can enable to identify the root cause?
3. Are there any configuration changes required for Kutt to work correctly in this setup?

Thank you for your help!

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