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Security aspects of cloud computing

Shift in responsibility

One important change triggered by the rise of cloud computing is a shift in responsibility. In the pre-cloud world, a system administrator was responsible for taking care of the system, installing security patches and fixes, securing the network, setting up firewalls and monitoring the operation state of servers.

With cloud computing, this has changed considerably: The system administrator is still responsible for the bare hardware servers. However, the user-created instances (virtual machines) running on these servers are the sole responsibility of the user who launched them. This includes any activity going on inside the instances while they are running as well as all of their communication with the outside world.

Large compute ressources and unrestricted high-speed internet access make cloud instances an attractive target for outside attackers. Users are obligated to keep their instances secure and up-to-date.

General security recommendations

  • SSH access: Always use key based authentication instead of a plain password.

  • Keep the operating system and all installed packages of your instances up to date.

  • Make sure to always use the most recent of the officially provided cloud images when launching a new instance.

  • Configure the internal firewall of your instances using iptables to add another layer of security in addition to the security groups.

  • Do not rely on any global cloud site firewall, its configuration might change without prior notice. If in doubt, ask the site administrators!

If you have detected a possible security problem with an instance, please contact the site administrators immediately and ask for support. They will to advise you on how to proceed.

Best practices for remote port access

SSH port forwarding

SSH is able to forward a port through a tunnel and make it available to your local computer only. No security group rule needed! So e.g. to access a server listening on port localhost:8080 of your instance, you forward it to on your local computer by adding the following to your SSH call: -L A server serving a website would then be available at

Further information:

Well defined remote IP range

Allow access from only a subset of IP addresses, e.g. limit this to your institution's IP address range. For Bielefeld University this would be, which amounts to only 0.002% of the world's IPv4 addresses, thereby drastically reducing the attack surface.

Determine your institution's IP address range and convert it to CIDR notation
  1. Use the european internet registry search to find the IP address range for your institution.

  2. Search for your institution first, e.g. Universitaet Bielefeld and find the organisation: ID (e.g. ORG-UB29-RIPE).

  3. Now search again, but this time for the ID, after selecting Inverse lookup and checking the box next to org.

  4. Look for the line inetnum: containing your institution's IP address range, e.g.

    inetnum: -

  5. Transform the IP address range into CIDR notation using a calculator.

  6. Enter the start of the range into the field IP Address.

  7. Adjust the Mask Bits (16 is a good starting point) until the end of your institution's IP range matches (or is included in) the range shown in the field CIDR Address Range.

  8. Use the Net: CIDR Notation from the calculator to configure the Remote CIDR of your security group rule (e.g.

The default security group (which all new instances get) should not be touched. Create a new one instead, add your rules and attach it only to the instances you need outside access to.

Further information:

Application security

Many applications support authentication (e.g. username and password). Use it to stop any outside attacks that were (easily) able to guess your instance's IP and port (which are not secret by any means). It is also highly recommended to protect your network traffic from prying eyes using TLS which is available inside almost all server applications, especially webservers.

Feel free to take a look at the tutorial Secure hosting of a public Web Server for guidance.

Always change the default credentials of services as these are well known and will be probed as soon as the service is exposed to the internet.