NYT has posted a deep look into the efforts to salvage Healthcare.gov.
As a small coterie of grim-faced advisers shuffled into the Oval Office on the evening of Oct. 15, President Obama’s chief domestic accomplishment was falling apart 24 miles away, at a bustling high-tech data center in suburban Virginia. ...
For 90 excruciating minutes, a furious and frustrated president peppered his team with questions, drilling into the arcane minutiae of web design as he struggled to understand the scope of a crisis that suddenly threatened his presidency.
“We created this problem we didn’t need to create,” Mr. Obama said
The website had barely been tested before it went live, so a large number of software and hardware defects had not been uncovered. Fixing the account creation software simply exposed other problems; people still could not register to buy insurance. A system intended to handle 50,000 simultaneous users was fundamentally unstable, unable to handle even a tiny fraction of that. As few as 500 users crippled it
It's a good read that covers some of the complexities involved in a large scale software project.