If you're using AWS CodeDeploy along with an EC2 Auto Scaling Group (ASG), you might think you're all set for seamless deployments and scalability.
But here's an important detail that often gets missed — and it can cause serious headaches if ignored.
⚙️ Auto Scaling Behavior with CodeDeploy
When your ASG scales out (i.e., launches new EC2 instances), AWS will automatically deploy the most recent successful revision from CodeDeploy to those new instances.
✅ This helps keep your environment consistent without manual intervention.
⚠️ The Hidden Danger: Multiple Deployment Groups
Here's where it gets tricky:
💣 If your Auto Scaling Group is attached to multiple CodeDeploy deployment groups, you could end up with:
- Deployment conflicts
- Unhealthy EC2 instances
- Auto Scaling flapping (repeated instance termination and relaunch)
- Inconsistent application versions across your fleet
This behavior happens because multiple deployment groups may try to manage the same instance, leading to confusion and failure in lifecycle event hooks.
✅ Best Practices
🔹 Attach only one CodeDeploy deployment group to each Auto Scaling Group
🔹 Ensure the CodeDeploy agent is installed and running on all instances
🔹 Use lifecycle hooks properly so instances are fully ready before entering service
🔹 Monitor deployments with CloudWatch alarms or deployment events
💡 Summary
When your ASG scales out, CodeDeploy takes care of deploying the last successful revision — but only if the setup is correct.
Be mindful of deployment group associations, and you’ll save yourself from surprise production outages or misbehaving EC2 fleets.
Would love to hear your experiences — have you faced this before? Drop a comment! 👇
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