Fear of no choice is starting to help Amazon’s cloud rivals.

Amazon’s web-services division has monopoly-like features — it is huge and growing, and size makes it operationally and financially more efficient. Yet Jeff Bezos’ company won’t walk away with all the spoils. Customers are worried about being locked in, and that will keep competitors in business.

Companies have come to realize it is simpler, cheaper and more convenient to store data and run applications on servers owned and operated by the likes of Amazon, Alphabet and Microsofts. Uncertainty over the cost implications is receding rapidly, according to surveys conducted by Bain and Morgan Stanley and highlighted by Kleiner Perkins’s Mary Meeker in her annual “Internet Trends” presentation last week.

The providers of cloud services have grown rapidly as a result. First-quarter revenue at Amazon Web Services was about 3.5 times as big as in the same period three years ago. At $3.7 billion for the period, it accounted for more than 10 percent of Amazon’s total sales, and it was by far the most profitable slice. The operating margin for Amazon Web Services has nearly doubled over the last two years to around 25 percent.

Not coincidentally, information technology managers have started to worry about the difficulty of switching cloud suppliers — a particular problem if one outfit, like Amazon Web Services, comes to dominate. This concern rocketed between 2012 and 2015, according to Ms. Meeker, with the proportion of respondents bothered by it surging from 7 percent to 22 percent.