EC2 Instance Recovery | Overview.

twtech Overview of EC2 Instance Recovery:

View:

•       How EC2 Instance Recovery works,
•       What AWS handles for twtech,
•       Best practices for using it with monitoring and automation.

1. The Concept: EC2 Instance Recovery

EC2 Instance Recovery is an automated process that brings a failed EC2 instance back into a healthy state without replacing the instance.
It’s tied to CloudWatch Alarms on EC2 system status checks.

• System Status Checks → Monitor AWS infrastructure health (host hardware, network, power, etc.).
• Instance Recovery kicks in when these checks fail, but the instance itself is still healthy (OS-level is fine).

 Important: 

EC2 Instance Recovery is different from Auto Scaling replacement.

 EC2 Instance Recovery restores the same instance (keeping instance ID, private/public IPs, Elastic IPs, attached volumes, and metadata intact).

2. How It Works

1. CloudWatch monitors EC2 status checks (system & instance).
2. If a system status check fails, a CloudWatch Alarm is triggered.
3. The alarm action = Recover this instance.
4. AWS automatically reboots the instance onto new healthy hardware behind the scenes.

• Preserves:
• Instance ID
• Elastic IPs & private IPs
• Data on attached EBS volumes
• Instance metadata (tags, IAM role, placement group membership, etc.)

3. Supported Instances

• Instance Types: Only some types support automatic recovery (most Nitro-based instances and newer generations: M5, C5, T3, R5, etc.).
• Storage: Must use EBS-backed volumes (instance store volumes are ephemeral and won’t be preserved).
• Placement Groups: Instances in cluster placement groups can be recovered, but AZ may change.

4. Key Features

• Automatic hardware migration → if host fails, AWS moves instance to healthy host.
• No user intervention required (after alarm setup).
• Minimal downtime compared to manual stop/start.
• Preserves identity → critical for stateful workloads.

5. When Recovery Triggers

• Loss of power to the underlying hardware.
• Physical host hardware failure.
• AWS networking issue affecting host.
• Software issues on AWS’s physical host layer.

Note: 

If instance status check fails (OS crash, kernel panic, app crash), EC2 recovery will not fix it — twtech would need reboot, rebuild, or Auto Scaling.

6. Architecture Flow

• EC2 Instance → monitored by CloudWatch Status Checks
• CloudWatch Alarm (on “StatusCheckFailed_System”)
• Alarm → Recover Instance action
• AWS migrates instance → launches it on new healthy hardware → reattaches volumes, network, and metadata

7. Advanced Use Cases

• Critical Single-Instance Workloads (databases, legacy apps, etc.).
• Production Environments where instance ID persistence is required (vs Auto Scaling replacement).
• High-availability setups where recovery is a faster safety net than manual intervention.
• Cost-conscious workloads — recovery avoids re-provisioning.

8. Best Practices

• Always enable detailed monitoring for faster detection (1-minute granularity).
• Create CloudWatch Alarms for both:
• StatusCheckFailed_Instance (OS-level issues)
• StatusCheckFailed_System (hardware-level issues → recovery supported)
• Combine recovery with:
• Auto Scaling Groups for instance replacement if app fails.
• Route 53 health checks to reroute traffic during downtime.
• Use CloudWatch Composite Alarms to escalate when multiple instances in a tier fail.
• Ensure EBS volumes are backed up (snapshots) in case recovery does not succeed.

Final thoughts:

•        EC2 Instance Recovery is AWS’s built-in safeguard against hardware and system-level failures, giving twtech automatic resilience without losing its instance’s identity.
•        For app-level resilience,  EC2 Instance Recovery combine  Auto Scaling, health checks, and backups.