Implementing feature flags in container environments with AWS AppConfig

This article explains how to implement feature flags in containerized environments using AWS AppConfig with the sidecar pattern, enabling runtime configuration changes without container redeployments.

• AWS AppConfig Agent runs as a sidecar container, exposing configuration via localhost:2772 HTTP endpoint
• Agent handles authentication, polling, caching, and graceful degradation automatically
• Identical deployment pattern works across ECS and EKS with any programming language
• Feature flags decouple configuration changes from container restarts and redeployments
• Agent polls AWS AppConfig at configurable intervals (default 45 seconds) and updates local cache transparently
• Supports multi-variant flags for different user segments with conditional rules
• Deployment strategies enable gradual rollouts with automatic rollback on CloudWatch alarm triggers
• Applications query agent inline without caching, receiving responses in microseconds

The sidecar pattern eliminates redeployment overhead, provides sub-millisecond configuration reads, and delivers production safety mechanisms for feature management at scale.