It seems that Amazon S3 is perfectly situated to act as a content delivery network, competing with the likes of Akami as long as you don't mind getting your hands dirty.
S3 supports your own domain names when setup as a CNAME with a bucket of the same name, but requires you to manually synchronize the files that it hosts.
On the cost side, other providers such as SimpleCDN boast one-off fees per file hosted with no additional bandwidth or storage charges and while Amazon S3 comes a close second with it's low fees it still doesn't support some features we need.
Automatic Sync
Yes, a big feature that S3 doesn't have - automatic syncing of image files from your website to S3, at least not in a fully transparent web-hosting friendly way.
Tools exist such as S3Sync to find modified files and upload them to S3, however these usually require more access than the majority of webhosts provide and aren't available on Windows or <your J2EE container of choice>.
SimpleCDN provide 'AutoCDN', which by prefixing your images with http://dl<your-account-id>.simplecdn.com/autocdn/<your-autocdn-folder>/ their servers will cache your images and serve them via their distributed CDN without any intervention required.
To add insult to injury, Amazon S3 doesn't support FTP upload, although this capability could be added relatively easily with third party software (and it's a project I'm considering) it seems that Amazon are by far more targeted at developers, narrowing the selection of people who might want to adopt it.
Pricing
Taken directly from SimpleCDN's pricing page for a single 85 KiB image serving 50,000 hits a day for a year.
| CDN | Bandwidth | Storage | Upload BW | Service Fees | Total | Compared |
|---|---|---|---|---|---|---|
| SimpleCDN | $0.00 | $0.00 | $0.00 | $0.10 | $0.10 | - |
| Amazon S3 | $192.32 | $0.00 | $0.00 | $0.00 | $192.32 | + $192.22 |
| Nirvanix | $266.29 | $0.00 | $0.00 | $0.00 | $266.29 | + $266.19 |
| Limelight | $547.37 | $0.00 | $0.00 | $0.00 | $547.37 | + $547.27 |
| Akamai | $1,449.80 | $0.00 | $0.00 | $0.00 | $1,449.80 | + $1,449.70 |
| CacheFly | $269.85 | $0.49 | $0.00 | $3,588.00 | $3,958.33 | + $3,958.23 |
Although this comes from the providers own data and is presumed to be at least a little bias, their pricing structure for small or even large images really blows the competition away (Amazon have since reduced the cost outbound bandwidth to $0.10 per GiB, reducing the total to $148).
Disadvantages
Personally I wouldn't consider Amazon ready for mainstream content distribution, especially if you have a large customer base in Australia or generally Asia.
- It's not transparent to developers
- No Asia or Australia coverage
- No video encoding services
With the exception of additional data-centers which are largely in Amazon's hands you can implement the others, but it requires developer time and additional costs (your own servers or Amazon EC2) for video conversion and/or hosting.
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