I need some guidance on a multi container docker compose file and if this looks correct

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Summary

A developer shared a docker-compose.yml file attempting to orchestrate a complex media stack (Jellyfin, Sonarr, Radarr, etc.) but used a single network without proper volume persistence or dependency management. The configuration relied on Docker’s default bridge network, causing inter-container communication failures. The immediate consequence was application startup errors and data loss risk upon container restart. The core misconfiguration involved missing restart policies and resource constraints, leading to a fragile, non-production-ready environment.

Root Cause

The root cause was a fundamental misunderstanding of Docker Compose’s state management and networking isolation. The user attempted to map multiple services to the host network directly or failed to define explicit internal networking, resulting in DNS resolution failures between containers (e.g., Sonarr unable to reach Prowlarr). Furthermore, the absence of named volumes or explicit bind mounts meant that database files and configuration states were stored in ephemeral anonymous volumes, risking total data loss on container removal.

  • Missing Volume Definitions: Configuration directories were not mapped to the host, making the setup non-persistent.
  • Undefined Network Aliases: Services could not resolve each other by service name (e.g., http://jackett:9117).
  • Lack of Health Checks: Dependent services started before their upstream dependencies were ready to accept connections.
  • Insecure Permissions: Running media applications as root without PUID/PGID environment variables caused file permission issues on the host’s mounted media folders.

Why This Happens in Real Systems

This is a classic “Happy Path” failure. Docker tutorials often show single-container deployments, skipping the complexity of inter-service orchestration. New users assume that simply defining a service in a YAML file guarantees connectivity, ignoring that Docker creates an isolated network bridge. In real systems, services require explicit handshaking (waiting for ports to open) and service discovery. The user likely copy-pasted snippets from documentation without understanding the infrastructure as code principles required to make the stack resilient.

  • Tutorial Gap: Most beginner guides don’t cover “cascading failures” where a database not being ready kills the application.
  • Default Settings Trap: Docker’s defaults (like restart: no and anonymous volumes) are safe for testing but disastrous for production data persistence.
  • Visual vs. Logical: Seeing containers “Running” in the UI does not mean the applications inside are functional or communicating.

Real-World Impact

In a production or homelab environment, this configuration leads to immediate instability. If the host reboots, the entire media stack comes up in a broken state due to race conditions. Data integrity is compromised if configuration files are not persisted, requiring a full re-setup. Furthermore, without resource limits, a single misbehaving container (e.g., a stuck Transcode process) can consume all available host resources, crashing the entire server.

  • Zero Data Persistence: A single docker-compose down command deletes all user settings and watched history.
  • Service Discovery Failure: The stack effectively forms “silos” where apps cannot trigger automations (e.g., Sonarr cannot tell Prowlarr to search).
  • Security Vulnerability: Running containers without user mapping often requires privileged access to the host filesystem, exposing the host to compromise.

Example or Code (if necessary and relevant)

This represents the corrected structure required for the user’s stack. It introduces dependency checks, explicit networking, and persistent volumes.

version: "3.8"
services:
  jellyfin:
    image: jellyfin/jellyfin
    user: 1000:1000
    network_mode: "host" # Or use bridge with port mapping
    volumes:
      - /path/to/jellyfin/config:/config
      - /path/to/media:/media
    restart: unless-stopped
    # Health checks ensure dependent services wait for this one
    healthcheck:
      test: ["CMD-SHELL", "curl -f http://localhost:8096 || exit 1"]
      interval: 30s
      timeout: 10s
      retries: 3

  sonarr:
    image: linuxserver/sonarr
    depends_on:
      jellyfin:
        condition: service_healthy # Waits for Jellyfin to be ready
    environment:
      - PUID=1000
      - PGID=1000
      - TZ=America/New_York
    volumes:
      - /path/to/sonarr/config:/config
      - /path/to/media:/media
    ports:
      - "8989:8989"
    restart: unless-stopped
    networks:
      - media-net

  prowlarr:
    image: linuxserver/prowlarr
    environment:
      - PUID=1000
      - PGID=1000
    volumes:
      - /path/to/prowlarr/config:/config
    ports:
      - "9696:9696"
    restart: unless-stopped
    networks:
      - media-net

networks:
  media-net:
    driver: bridge

How Senior Engineers Fix It

Senior engineers approach container orchestration with the mindset of resilience and observability.

  1. Decoupling via Networks: They explicitly define custom bridge networks (networks: media-net) rather than relying on the default, isolating the stack and enabling secure internal communication.
  2. Dependency Management: They implement depends_on with health checks. This ensures a database is fully up before the app tries to connect, preventing race conditions.
  3. State Isolation: They strictly map configuration folders to the host using absolute paths and enforce user permissions (PUID/PGID) to ensure file ownership is consistent across backups and restores.
  4. Infrastructure as Code (IaC): The YAML file is version-controlled. No manual container editing via UI is allowed; the state is defined entirely in code.
  5. Automation: They add monitoring (e.g., Watchtower for updates or Grafana for metrics) to detect when a container enters a CrashLoopBackOff or unstable state.

Why Juniors Miss It

Juniors often treat Docker as a “lightweight VM” rather than a process manager. They focus on getting the container to start rather than ensuring it integrates. They rely on the Docker Desktop UI to tweak settings (Port Mappings, Environment Variables) rather than codifying them, leading to Configuration Drift. They miss the concept of Orchestration entirely, not realizing that containers in a compose file are isolated by default and need explicit instructions to talk to one another.