Gartner expects the top 10 providers to account for nearly 70 per cent of the IaaS market by 2021, up from 50 per cent in 2016.

"The increasing dominance of the hyperscale IaaS providers creates both enormous opportunities and challenges for end users and other market participants," said Sid Nag, research director at Gartner.

"While it enables efficiencies and cost benefits, organisations need to be cautious about IaaS providers potentially gaining unchecked influence over customers and the market. In response to multicloud adoption trends, organisations will increasingly demand a simpler way to move workloads, applications and data across cloud providers' IaaS offerings without penalties."

Table 1. Worldwide Public Cloud Service Revenue Forecast (Billions of US Dollars)

BPaaS = business process as a service; IaaS = infrastructure as a service; PaaS = platform as a service; SaaS = software as a service
Note: Totals may not add up due to rounding.

Source: Gartner (April 2018)

Software as a service (SaaS) remains the largest segment of the cloud market, with revenue expected to grow 22.2 per cent to reach $73.6 billion in 2018. Gartner expects SaaS to reach 45 per cent of total application software spending by 2021.

"In many areas, SaaS has become the preferred delivery model," said Mr Nag. "Now SaaS users are increasingly demanding more purpose-built offerings engineered to deliver specific business outcomes."

Within the platform as a service (PaaS) category, the fastest-growing segment is database platform as a service (dbPaaS), expected to reach almost $10 billion by 2021. Hyperscale cloud providers are increasing the range of services they offer to include dbPaaS.

"Although these large vendors have different strengths, and customers generally feel comfortable that they will be able to meet their current and future needs, other dbPaaS offerings may be good choices for organisations looking to avoid lock-in," said Mr Nag.

Although public cloud revenue is growing more strongly than initially forecast, Gartner still expects growth rates to stabilise from 2018 onward, reflecting the increasingly mainstream status and maturity that public cloud services will gain within a wider IT spending mix.