Banking isn't easy these days.

More than six years after Lehman Brothers' collapse, the number of U.S. commercial banks has dropped more than 20 percent, to 5,500 companies. Tight new regulations have put the squeeze on the industry, along with increasing competition from online financial services startups.

In response, some of the largest financial services firms have shown early and active interest in OpenStack, the open source cloud architecture platform, as they attempt to roll out new mobile and online banking services to head off disruption.

American Express, Wells Fargo, and Spain-based BBVA are all experimenting with OpenStack in their private data centers, with sources indicating that AmEx's production deployment has reached 40,000 cores.

Behind the interest lies a race to deploy new customer-facing applications, as banking increasingly shifts from brick-and-mortar branches to mobile and web apps.

“Applications are the main way we give value to our customers,” Jose-Maria Sanjose, BBVA global head of innovation, said in November at the Paris OpenStack Summit.

Low-cost storage for massive amounts of transaction data is also key. "I've heard customers on Wall Street say it's cheaper to never delete something than figure out what I'm allowed to delete" under regulatory rules, says Larry Wikelius, director of ecosystems and partner enabling at ARM-based processor maker Cavium. Several firms are testing OpenStack in conjunction with open source object storage system Ceph, Wikelius says.

Bank of America and TD Bank are also pursuing significant OpenStack deployments, say sources, with both companies turning up at the OpenStack Summit in Vancouver this week.

"There are hundreds of startups with a lot of brains and money working on various alternatives to traditional banking," JPMorgan Chairman and CEO Jamie Dimon wrote in a recent letter to shareholders. "Silicon Valley is coming."