Amazon EC2公网IP无法加载，使用3-4个月的实例突发故障求助

Hey there, sorry to hear your EC2 instance started acting up after working smoothly for 3-4 months! As someone who’s been through this as a new cloud user, let’s break down the most likely issues and how to check them out step by step:

• First, confirm your instance is actually running
  Head to your AWS EC2 console, find your instance, and check the "Instance state" column. If it’s stopped or terminated, that’s the immediate issue. Instances can stop automatically due to billing discrepancies (double-check your account payment status) or AWS detecting a hardware fault. If it’s stopped, right-click and select "Start instance"—give it 1-2 minutes to boot fully before testing access again.

• Check your security group settings (this is the #1 newbie gotcha)
  Security groups act as the external firewall for your EC2 instance. Go to your instance’s details page, click the linked security group under "Security" > "Security groups". Make sure there are inbound rules allowing traffic on the ports you need:

  • For regular HTTP access, add a rule for HTTP (80) with source 0.0.0.0/0 (or your specific IP address if you want tighter security)
  • For HTTPS, add a rule for HTTPS (443) the same way
  • If you’re using a custom port (like 3000 for a development server), don’t forget to allow that port too!

• Verify your public IP hasn’t changed
  If you didn’t set up an Elastic IP, EC2 instances get a temporary public IP that resets every time the instance stops and starts. If your instance restarted for any reason, your old IP won’t work anymore. Check the current public IP in the EC2 console and test accessing that directly first. If you want a permanent IP, you can allocate an Elastic IP in the console and associate it with your instance.

• Troubleshoot issues inside the instance
  If the instance shows as running but is still unreachable, the problem might be on the server itself:

  • Try connecting via the EC2 Serial Console (if enabled) or Session Manager (most default AMIs have the SSM agent pre-installed). This lets you access the instance without needing external network connectivity to debug.
  • Check if internal firewalls are blocking traffic. On Linux, run sudo iptables -L to list firewall rules and confirm your ports are allowed. On Windows, check the Windows Firewall settings.
  • If you can’t connect at all, detach the root volume from this instance, attach it to a working EC2 instance, and inspect system logs (like /var/log/syslog on Linux) to look for boot failures or crash errors.

• Rule out DNS problems
  If you’re using a custom domain instead of the public IP, make sure your DNS A record is pointing to the correct current IP of your instance. DNS changes can take a few minutes to propagate, so always test with the raw public IP first to eliminate this as a cause.

内容的提问来源于stack exchange，提问作者g820509