Amazon’s plan to double its tech workforce in Chicago illustrates the furious land grab that continues in cloud computing.

Amazon says it plans to add 400 tech jobs in Chicago, across various business lines, including its Amazon Web Services division and its transportation business.

Amazon opened its Chicago office just four years ago and soon decided to double it. More than half that headcount is technical staff, many of them doing sales and support for AWS, its fast-growing business of hosting computer resources for companies big and small.

Businesses have been steadily moving their software and data from their own computers to those operated by Amazon and others, such as Google, Microsoft and IBM.

Cloud computing is one of the fastest-growing parts of the technology industry. Research firm IDC expects global sales to top $200 billion this year, an increase of 24 percent from 2018.

Persuading companies to move their most sensitive data and most critical systems is complicated, requiring engineers in sales and support roles.

Google also has been hiring technology talent aggressively in Chicago for its cloud-computing business. It’s one reason Google leased additional space in a second building in Fulton Market.

Google now has more than 1,200 workers in Chicago, nearly one-fourth of whom are in technology jobs. But unlike Amazon, many of Google’s tech workers in Chicago are involved with developing core products, ranging from search software to hardware.