github.com/containrrr/watchtower

Watchtower is actually a standalone Docker container application rather than a Go library you import. It monitors and auto-updates running containers, which sounds convenient but requires careful consideration in production. The runtime behavior is polling-based with configurable intervals (default 5 minutes), creating predictable but constant Docker API load. Memory footprint is reasonable (~15-30MB), but the Docker socket access requirement is a significant security consideration.

Configuration is environment variable-driven which integrates cleanly with container orchestration, but the lack of structured config files makes complex setups verbose. Logging is straightforward but basic - you get update notifications and errors, though correlation with application-level issues requires external tooling. The notification system (Slack, email, etc.) works reliably but adds dependencies.

The biggest operational concern is the lack of granular rollback mechanisms and the potential for simultaneous updates causing cascading failures. Health check integration exists but timeout handling during updates can be aggressive. For small deployments it's useful, but for production systems, proper CI/CD pipelines with staged rollouts provide better control and observability.

Watchtower is primarily a standalone Docker container for automating container updates, not a Go library you'd import into your code. While the Go package exists on GitHub, the typical usage is deploying Watchtower as a container that monitors and updates your other containers. This creates confusion for developers expecting a traditional Go SDK.

The configuration is environment-variable driven, which works well for simple deployments but becomes unwieldy for complex scenarios. Documentation covers the basics adequately, with examples for common Docker Compose setups. Error messages when filters are misconfigured can be cryptic, and debugging requires container log inspection rather than standard Go debugging workflows. The GitHub issues show decent maintainer responsiveness, but many questions reveal confusion about its operational model.

If you do need to work with the codebase directly (for contributions or customization), the project structure is reasonably organized, though lacking comprehensive inline documentation. The learning curve is moderate if you understand Docker well, steeper if you're trying to extend functionality programmatically.

Watchtower is primarily designed as a standalone Docker container that monitors and updates other containers. If you're trying to use it as a Go library in your application, you'll find the experience frustrating. The codebase is structured around CLI execution rather than library consumption, with most functionality tightly coupled to command-line flags and Docker Compose integration.

The documentation focuses almost entirely on running Watchtower as a container with environment variables and Docker labels. There are virtually no examples showing how to import and use it programmatically in Go code. The internal packages aren't designed with external consumption in mind, making it difficult to understand which types and functions are intended for public use. Error handling tends to log directly rather than returning structured errors you can handle.

If you need automated Docker updates in your Go application, you're better off using the Docker SDK directly and implementing your own update logic. Watchtower shines when used as intended: a standalone container you deploy alongside your services. As a Go package dependency, it creates more problems than it solves.