We do SaaS for the financial industry, and we started out creating a separate virtual network with multiple VMs for each customer. Router firewalling, iptable l

We do SaaS for the financial industry, and we started out creating a separate virtual network with multiple VMs for each customer. Router firewalling, iptable lockdown, IP whitelisting to customer IP range. Encrypted disks (backed by SAN) for database storage with different keys per customer. Etc. So we had to scale up our deployment process to multiple concurrent migrations per customer pretty much from day one. The downside of this is that customers need to be big to afford the constant overhead of physically renting the machinery to serve them, administer them etc. So we're moving towards multi-tenancy from the other angle, aiming at smaller firms with less stringent data security requirements.