Image: solidprogramming/dockercontainerupdatechecker

DockerContainerUpdateChecker

Checks running Docker containers for updated image digests and sends a Telegram notification when the detected update state changes. Scheduled runs and manual triggers are handled through Hangfire.

Configuration

The app reads appsettings.json and then a local override file.

Local override file resolution:

1. /config/appsettings.Local.json if /config exists
2. otherwise appsettings.Local.json in the application directory

If the local file does not exist yet, the app creates a starter file automatically at the resolved location on first launch.

{
  "Server": {
    "Port": 8080
  },
  "Localization": {
    "Culture": "de-DE"
  },
  "Scheduler": {
    "Cron": "0 */6 * * *",
    "RunOnStartup": false
  },
  "Docker": {
    "Endpoint": ""
  },
  "Telegram": {
    "BotToken": "123456:replace-me",
    "ChatId": "123456789"
  },
  "Monitoring": {
    "ExcludedContainers": [ "unraid-db" ]
  },
  "Storage": {
    "DataDirectory": "/config/data"
  }
}

Set Localization:Culture to a .NET culture such as de-DE or en-US to control localized date and time formatting in logs and notifications. Set Scheduler:RunOnStartup to true if the container should execute one immediate update check after startup instead of waiting for the next cron occurrence.

Unraid / Docker notes

• Mount the Docker socket: /var/run/docker.sock:/var/run/docker.sock
• Mount a single parent folder from the host to /config, for example /mnt/user/appdata/dockercontainerupdatechecker:/config
• The generated appsettings.Local.json will then be created at /config/appsettings.Local.json
• Persistent state will be stored under /config/data
• Map a host port to the internal container port, default 8080
• The Hangfire dashboard is available at /hangfire

Docker / Podman endpoint selection

The app resolves the container API endpoint in this order:

1. Docker:Endpoint from configuration
2. DOCKER_HOST from the environment
3. Built-in default

Defaults:

• Windows: npipe://./pipe/docker_engine
• Linux: unix:///var/run/docker.sock

Examples:

• Docker on Linux / Unraid: unix:///var/run/docker.sock
• Podman socket on Linux: unix:///run/user/1000/podman/podman.sock
• Podman or Docker via TCP: tcp://127.0.0.1:2375

Behavior

• By default, all running containers are checked
• Individual containers can be excluded through Monitoring:ExcludedContainers
• Hangfire uses in-memory storage, so dashboard history is cleared after a container restart
• The app sends a Telegram startup test notification after successful startup validation
• The last functional update state is stored separately in /config/data/last-update-state.json by default so notifications remain stable across restarts

Telegram troubleshooting

• If Telegram returns 400 Bad Request, a common reason is that the target user or group has not started a chat with the bot yet
• For direct messages, open the bot in Telegram and send /start once before testing notifications
• If the problem remains, verify that the configured Telegram:ChatId is correct

Create a Telegram bot

1. Open Telegram and start a chat with @BotFather.
2. Run /newbot and follow the prompts to create a bot.
3. Copy the bot token from BotFather and set it as Telegram:BotToken.
4. Open your new bot in Telegram and send /start once so the bot can message you directly.
5. Send any additional message to the bot, then open https://api.telegram.org/bot<your-bot-token>/getUpdates in a browser.
6. Find the chat object in the JSON response and copy the numeric id value into Telegram:ChatId.

After both values are configured, restart the app and it will send a startup test notification after successful validation.