Some Test Data...

Hitting a Wordpress front page using the wonderful siege load testing tool.

Siege will use a somewhat realistic pattern of 20 concurrent users each loading the page every 10 seconds. Every page load translates to several HTTP requests, as it requests dependent URLs.

This amounts to ~40 requests per second, or ~2,400 requests per minute, or ~3.5M requests per day.

# siege -c20 -d10 -t30m -v https://wpdemo.example.com/
{	"transactions":			       71161,
	"availability":			      100.00,
	"elapsed_time":			     1799.07,
	"data_transferred":		      812.31,
	"response_time":		        0.05,
	"transaction_rate":		       39.55,
	"throughput":			        0.45,
	"concurrency":			        2.10,
	"successful_transactions":	       71162,
	"failed_transactions":		           0,
	"longest_transaction":		        4.61,
	"shortest_transaction":		        0.01
}

Lambda concurrency was surprisingly low, between 6 and 9 over the whole test.

If we were to extrapolate that to a full day of traffic, we'd have ~3.5M requests per day.

This test traffic averages to ~40 milliseconds of Lambda compute per request (front page is ~250msec and static assets are more like 5msec each).

For Lambda:

40ms * 3.5M requests * $0.0000000083 per ms at 0.5 GB is about ~$1.16 per day.

For API Gateway:

3.5M requests * $0.0000012 per request is about $4.2 per day.

So there you have an extremly high-available high-traffic Wordpress site with superb response times at ~$5 per day.

Keep in mind: That is a huge buttload of traffic that most Wordpress installations will never see. Not even close.

And for every request less than that, you'll pay less. That's the awesome thing about AWS Lambda.

And also keep in mind that this is without any caching by a browser or by any CDN. If there'd been some CDN, pretty much all static requests would never hit the Lambda function, reducing the request count to maybe one fifth of the numbers above.

Please note we're not counting AWS egress traffic or RDS/Aurora costs. Those would be the same for a traditional Wordpress deployment. The database tends to be bored anyway -- for the above test, Aurora Serverless with just 1 ACU was idling at 10-15% CPU. And EFS cost for a few dozen MBs is negligible (below $0.000/day).

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