Connectivity Issue to EC2 Instances

That definitely sounds frustrating — especially if it’s happening across multiple accounts and regions like eu-west-2. A few things that might help narrow it down:

Check AWS Health Dashboard (https://health.aws.amazon.com/): Sometimes these types of widespread blips don’t show in CloudWatch or local logs, but AWS will quietly post regional issues here.

VPC Flow Logs: Turn these on (if not already) to catch packet-level drops. If the disconnects are network-related vs. app-level, they’ll show up there.

NTP drift or system clock issues: In rare cases, EC2s across accounts using similar AMIs or boot scripts might disconnect simultaneously due to SSL expiration or time-based auth failing (especially with webhooks, APIs).

Shared infrastructure event: Since this hit multiple accounts at the same time, it could be an availability zone-wide hiccup. Look at the AZs your instances are in — if they all align, it’s worth flagging that in another support case.

Migrating is a big move — so hopefully one of these helps pinpoint the root cause better than last time.

This is a concerning issue that you're experiencing with your EC2 instances in the eu-west-2 (London) region. The fact that it's happening across multiple instances and even different AWS accounts simultaneously suggests a potential underlying infrastructure or network problem rather than an issue with individual instances.

Here are some steps you can take to troubleshoot and potentially resolve the issue:

1. Check AWS Service Health Dashboard: First, verify if there are any reported issues or service disruptions in the eu-west-2 region that might be affecting your instances.

2. Monitor Instance Status: Ensure that your instances are in a "running" state and passing their status checks. Sometimes, underlying hardware issues can cause intermittent connectivity problems.

3. Review CloudWatch Metrics: Use AWS CloudWatch to monitor your instances' network performance metrics. Look for any patterns or anomalies during the times when the connectivity drops occur.

4. Examine System Logs: Check the system logs in the EC2 console for any error messages or warnings that might indicate the root cause of the problem. Look for issues related to network failures or unexpected disconnections.

5. Verify Network Configuration: Double-check your security groups, network ACLs, and VPC settings to ensure they're correctly configured and haven't been inadvertently changed.

6. Consider Using Elastic IP: If you're not already using Elastic IPs, consider associating them with your instances to maintain consistent public IP addresses.

7. Implement Auto-recovery: Configure automatic recovery for your instances. This will automatically recover instances if they become impaired due to underlying hardware issues.

8. Use EC2 Instance Connect: Try using EC2 Instance Connect as an alternative method to connect to your instances, which might help isolate whether the issue is related to your current connection method.

9. Engage AWS Support Again: Given the widespread nature of the issue and its impact on your services, it's worth escalating this to AWS Support again. Provide them with detailed logs, timestamps of the outages, and any other relevant information you've gathered from your troubleshooting efforts.

If these steps don't resolve the issue and AWS Support is unable to provide a satisfactory resolution, you might consider testing your workload in a different AWS region to see if the problem persists. This could help determine if it's a region-specific issue.

Remember to document all troubleshooting steps and their outcomes, as this information can be valuable for further investigation or if you need to escalate the issue within AWS.

Sources
Why am I having trouble connecting to my EC2 instances? | AWS re:Post
EC2 suddenly gets online and offline randomly | AWS re:Post
Troubleshoot issues with Amazon EC2 instances - Amazon Elastic Compute Cloud