Amazon websites in the UK and the US have been hit by outages over the past few days, with some reports claiming that at certain points less than a third of visitors have been able to access to site.

Between 10:03am and 10:23am yesterday (US time), only about 30 per cent of visitors managed to enter, according to mobile and internet management firm Keynote Systems, which tracks website performance.

After stabilising, again wobbled, and its availability dropped to about 68 per cent between 10:56am and 11:09am, said Shawn White, director of external operations at Keynote.

After that, the site went back to normal and remains that way at press time.

However, the technical gremlins also hit the company's UK online store on Monday.

The UK site first experienced problems at 6:06pm GMT, and its availability dropped as low as 38 per cent - meaning that about six of 10 people couldn't enter - but by 8:11pm the availability had climbed back to about 96 per cent, White said.

Asked for comment, Amazon said: "Some customers reported intermittent problems accessing Amazon retail websites on Monday morning. However, we are working to resolve the issues, and Amazon's web services are not affected."

Even people who managed to enter and browse the sites faced slow performance: while pages typically load in six seconds or less, that average climbed to about 15 seconds during the affected periods, White said.

Gomez, another website-monitoring firm, puts normal average response times at Amazon at between three seconds and 8.5 seconds, but that average rose to 14 seconds on Friday and stood in a range of between 2.5 seconds and 14 seconds on Monday.

On Friday, when the availability problems lasted about three hours, as well as on Monday, most shoppers having access problems were getting a cryptic error message saying "Http/1.1 Service Unavailable," which means nothing to non-technical people.

This indicates to White that whatever caused the problem proved hard to isolate, making it impossible for the company to configure its system to trigger a more intelligible alert acknowledging the problem in plain English.

White's guess is that a misconfiguration somewhere in the complex Amazon e-commerce system discombobulated unrelated pieces in its vast network of databases, data centres and application and web servers.

If this is indeed the cause of the problems, the lesson for Amazon and anyone else is to perform rigorous testing before making any alterations, especially when the change will have an effect on many moving parts in the system, White said.

"The more complex a system is, the more challenging it is to maintain, and a configuration problem here can cause problems somewhere else," he said.

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