Security considerations when running a VM

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Parent page: Cloud

On the cloud, you are responsible for the security of your virtual machines.

This document is not a complete guide, but will set out some things you need to consider when creating a VM on the cloud.

Keep the operating system secured

  • Apply security updates on a regular basis (see updating your VM).
  • Avoid using packages from unknown sources.
  • Use a recent image; for example, don't use Ubuntu 14.04 when Ubuntu 18.04 is available.
  • Use SSH key authentication instead of passwords. Cloud instances use SSH key authentication by default, and enabling password-based authentication is significantly less secure.
  • Install fail2ban to block brute-force attacks.

Network security

  • Limit who can access your service. Avoid using in the CIDR field of the security group form - in particular, don't create rules for "" in the default security group, which applies automatically to all project instances.
    • Be aware of the range you are opening with the netmask your are configuring.
  • Do not bundle ranges of ports to allow access.
  • Think carefully about your security rules. Consider the following:
    • These services aren't meant to be publicly accessible:
      • ssh (22) - this service allows interactive login to your instance and MUST NOT be made publicly accessible
      • RDP (3389) - this service allows interactive login to your instance and MUST NOT be made publicly accessible
      • mysql (3306)
      • postgresql (5432)
      • nosql
      • tomcat
      • ... many, many others
    • Some services are meant to be accessible from the internet:
      • Apache (80, 443)
      • Nginx (80, 443)
      • ... others
  • Configure your web server to use HTTPS instead of HTTP.
    • In many case HTTP should only be used to redirect traffic to HTTPS.
  • Do NOT run a mail server.

Updating your VM

In order to keep a VM's operating system secure, it must be regularly updated - ideally weekly, or as often as new packages become available. To upgrade a Linux VM choose the commands below for your particular distribution. Note you will need to reconnect to your VM after rebooting.


$ sudo apt-get update
$ sudo apt-get dist-upgrade
$ sudo reboot


$ sudo yum update
$ sudo reboot


$ sudo dnf update
$ sudo reboot

Further reading

An amazon article on securing instances:

HyperText Transfer Protocol