Debugging a Nightmare on EC2: A Day in the Life

January 7, 2008. I was knee-deep into one of those days that made me want to scream for help and maybe take a nice long nap afterward.

The Setup

At my company, we were running a lot of our services on Amazon Web Services (AWS), specifically EC2 and S3. We had built out a pretty solid infrastructure with some custom scripts for managing instances, monitoring, and logging. But today was going to be one for the books.

The Problem

The night before, I got an alert about 10 of our production servers crashing simultaneously. They were running a piece of critical software that powers a significant part of our service. The logs showed a weird segfault in our application code, but that only happened once and didn’t happen again on subsequent attempts.

The Investigation

I started by SSHing into one of the instances to check things out. The initial signs were pointing towards an issue with either the kernel or the underlying hardware. I ran some diagnostics like dmesg and top, but nothing jumped out at me as obviously problematic.

Memory Check

Memory seemed okay, so I decided to do a full memory dump using memtest86+. The results were inconclusive—no errors reported during testing, which could mean the memory was fine or that it just wasn’t enough for the tests.

Kernel Panic

Then came the kernel panic. This time, the logs gave me more clues: some obscure error related to the network stack. I thought maybe a recent update had messed something up, but rolling back didn’t help. The panic was consistent across all 10 instances, which made me suspect it might be an issue with EC2 itself.

AEC2

I spent hours trying different things, like restarting networking services and even rebooting the instances multiple times. Nothing worked, and I was starting to get frustrated. The last thing I did before calling it a night was set up some automated alerts to notify me if any changes happened on my end of AWS.

The Aftermath

The next morning, I woke up early to check on things because sleep just wasn’t coming. By the time I got back into the office, the instances were still down, and the situation felt like a losing battle. But then something clicked: what if it was an issue with EC2 itself? Could AWS be doing maintenance or experiencing some kind of internal problem?

I decided to ping our account manager at AWS, hoping for a quick fix or some advice. She pointed out that they were indeed doing routine maintenance and recommended checking the status page.

The Status Page

The EC2 status page confirmed it: there was an outage affecting multiple zones, including the one where we hosted our instances. This wasn’t just my problem; thousands of other users were likely facing similar issues. I felt a mix of relief (someone else had this issue too) and frustration (why couldn’t AWS catch it sooner?).

The Resolution

After the maintenance window ended, I tried to bring up one instance again. It booted successfully without any issues. I cautiously brought back the others, making sure everything was working as expected before pushing a new deployment.

Lessons Learned

This experience taught me a few things:

1. Always Have a Plan B: Even if you have redundancy built into your infrastructure, knowing when to cut over is crucial.
2. Stay Informed About Outages: Keep an eye on provider statuses and updates, especially during maintenance periods.
3. Document Everything: If something like this happens again, I’ll need detailed notes from the initial investigation.

Conclusion

As the day wound down, I felt a bit relieved that we had managed to get everything back online. But more than anything, it left me thinking about how quickly things can go south in a cloud environment and how important it is to be prepared for those inevitable hiccups.

For now, though, I’m just happy to be back home with the promise of a well-deserved nap.

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That’s my day in review. Maybe next time, we’ll have better luck avoiding this kind of nightmare on EC2.