Senior Vice President at Google Diane Greene Steve Jennings | Getty Images

Diane Greene, who was hired three years ago to build Google's cloud-computing business, is being replaced in that job by former Oracle executive Thomas Kurian. Google said on Friday that Kurian is joining Google Cloud on Nov. 26 and will take over the leadership role in early 2019. Greene will remain CEO of the business until then.

It's been a rocky tenure for Greene, who brought serious enterprise chops to Google, having previously co-founded and run VMware. She's staffed up the enterprise sales team and won business from the likes of Spotify and Snap, but Google has failed to eat into Amazon's massive lead in the market, and Microsoft has clearly established itself in second place. Greene, a director of Google parent company Alphabet since 2012, is staying on the board. Kurian spent more than two decades at Oracle, rising to the level of president of product development. In September he said he was taking "extended time off" in an email to employees, but he resigned before the end of the month.

Thomas Kurian David Paul Morris | Bloomberg | Getty Images

Greene wrote in a blog post on Friday that she, Google CEO Sundar Pichai and Urs Hölzle, Google's senior vice president for technical infrastructure, all interviewed Kurian for the job. Hölzle originally recruited Greene to the job, which she accepted when Google acquired her previous start-up Bebop for $380 million in stock. Greene's share of that was almost $150 million, which she said at the time she would donate to a donor-advised fund. "When I joined Google full-time to run Cloud in December 2015, I told my family and friends that it would be for two years," Greene wrote. "Now, after an unbelievably stimulating and productive three years, it's time to turn to the passions I've long had around mentoring and education." Amazon Web Services controls 34 percent of the cloud infrastructure services market, according to Synergy Research. Microsoft is second at about 15 percent, followed by IBM in third and Google in fourth, both with market share in the single digits. Alphabet raised eyebrows in its earnings call last month, when the company gave less information than it had in the past on the size and growth rate of the cloud unit.

In February, Pichai told analysts that the total cloud business, which includes applications for email, word processing and spreadsheets as well as public cloud infrastructure, was generating more than $1 billion in revenue per quarter. He said that, based on publicly available data from 2017, it was likely growing faster than any of its rivals. But when asked for an update in October, Pichai neglected to offer specifics, saying only that he's seeing "strong indicators" that the investment is paying off and that enterprise wins "turn into larger revenue deals over time." Some analysts were unimpressed. "There were notably no metrics in relation to the cloud business, which we view as not an overly encouraging sign," analysts from Atlantic Equities wrote in a report after Alphabet's earnings report. Under Greene's leadership, the Google Cloud Platform focused engineering resources on artificial intelligence and machine learning to give other companies the types of tools that had been powering Google's search and other services since its early days. Clients often touted the company's advanced technologies for running sophisticated workloads, but the bigger sums of money for core infrastructure were still going to AWS and Microsoft Azure. "They're not winning the boring lift-and-shift business — that goes directly to Amazon," said Maribel Lopez, an industry researcher at Lopez Research in San Francisco. "They have really good positioning around the innovative stuff, but the things they're not getting are the more basic things."

Facing Google's culture