As Amazon's cloud service continues to increase its market share, it's also showing more signs of locking in customers into bigger and longer-term contracts.

That trend was once again evident at Amazon Web Services' annual re:Invent conference last week, where executives highlighted the growth in partner deal size. Partner deals typically represent multiyear contracts with bigger companies as they involve large-scale projects.

Terry Wise, vice president of global alliances and channels at AWS, said in his keynote that the total deal size brought in by partner sellers has increased 3.5 times compared with last year, while the rate of growth in partner-led contracts is far outpacing the growth of AWS' overall business.

Those numbers show AWS customers making bigger upfront commitments, giving Amazon a more predictable revenue stream for future years, according to Jefferies analyst Brent Thill.

"It suggests customers are doing 'cannonballs' into the pool versus just dipping their toe in," Thill told CNBC. "Bigger commitments mean we have more confidence in revenue as most customers won't leave AWS once they commit."

AWS became popular with its pay-as-you-go model, which helped draw many start-ups because it only charged for the amount of computing power they used. But as AWS matured, and became more popular across businesses of all sizes, multiyear contracts with upfront commitments, typically preferred by corporate clients, have come to account for a larger share of its revenue.

Perhaps that explains why AWS started disclosing "performance obligations" this year, which it defines as future revenue "associated with commitments in customer contracts for future services that have not yet been recognized." In its most recent quarter, that amount grew to $17.8 billion, up from $16 billion in the second quarter and $12.4 billion in the first quarter.

It also added a line about such deal structures in its latest earnings filing, saying AWS offers certain services that are "offered as a fixed quantity over a specified term, for which revenue is recognized ratably."