Problem: AWS Lightsail Networking Issues – "Why Can’t I Connect to My Lightsail Instance?"

Problem: AWS Lightsail Networking Issues – "Why Can’t I Connect to My Lightsail Instance?"

Common Error Messages:

SSH Connection Error:
ssh: connect to host <IP> port 22: Connection timed out

HTTP(S) Connection Error:
curl: (7) Failed to connect to <domain> port 80: Connection refused

DNS Resolution Error:
ping: unknown host <domain>

AWS Lightsail Firewall Block:
An error occurred (InvalidInputException) when calling the OpenInstancePublicPorts operation:

The specified instance does not allow the requested port.

Issue:

AWS Lightsail instances sometimes become unreachable due to networking misconfigurations, firewall restrictions, or DNS failures. Common causes include:

• Firewall rules blocking traffic – Lightsail uses a built-in firewall that must explicitly allow inbound connections.
• Incorrect SSH key or permissions – Public key errors can prevent login access.
• Network routing issues – Outbound networking may be restricted.
• DNS misconfigurations – Domains not resolving properly to Lightsail instance IPs.

Fix: Troubleshooting AWS Lightsail Connectivity Issues

# Step 1: Check instance firewall and open required ports 
# (22 for SSH, 80 for HTTP, 443 for HTTPS)
$ aws lightsail get-instance-port-states --instance-name "MyInstance"

# If ports 22, 80, or 443 are listed as "closed," open them:
$ aws lightsail open-instance-public-ports 
    --instance-name "MyInstance" 
    --port-info fromPort=22,toPort=22,protocol=TCP
$ aws lightsail open-instance-public-ports 
    --instance-name "MyInstance" 
    --port-info fromPort=443,toPort=443,protocol=TCP

# Step 2: Verify SSH Key and Permissions
$ ssh -i my-key.pem ubuntu@<instance-public-ip>

# If successful, you should see a welcome message and last login info.
# If you get "Permission denied (publickey)," check your key permissions:
$ ls -l ~/.ssh/my-key.pem

# If the output shows "-rw-r--r--", fix permissions:
$ chmod 400 ~/.ssh/my-key.pem

# Step 3: Debug Firewall and Routing Issues
$ sudo iptables -L -v -n

# If the firewall policy blocks SSH, HTTP, or HTTPS, add rules:
$ sudo iptables -A INPUT -p tcp --dport 22 -j ACCEPT
$ sudo iptables -A INPUT -p tcp --dport 80 -j ACCEPT
$ sudo iptables -A INPUT -p tcp --dport 443 -j ACCEPT
$ sudo systemctl restart ufw  # Restart firewall service

# Step 4: Verify DNS and Domain Configuration
$ nslookup <your-domain>

# If you see "server can't find <your-domain>: NXDOMAIN," the domain 
# is misconfigured. Check Lightsail DNS settings:
$ aws lightsail get-domain --domain-name "mydomain.com"

# Ensure the A record points to your instance’s public IP.

# Step 5: Test Connectivity Using Debugging Tools
$ nc -zv <instance-public-ip> 22

# If "Connection refused," SSH is still blocked or not running.
$ traceroute <instance-public-ip>

# If routing stops midway, the network path may be broken.
$ curl -v http://<instance-public-ip>

# If the response includes "HTTP/1.1 200 OK," the web server is working.
# Step 6: Restart Instance and Retest
$ aws lightsail reboot-instance --instance-name "MyInstance"

# If all else fails, a reboot may resolve networking inconsistencies.

Need AWS Expertise?

If you're looking for guidance on Amazon Lightsail or any cloud challenges, feel free to reach out! We'd love to help you tackle your Lightsail projects. 🚀

Email us at: info@pacificw.com

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