问题
I hope this question isn't too rudimentary, but I'm confused...
In the S3 documentation I read:
All HTTP queries have an expiration parameter that allows you to set how long the query will be valid. For example, you can configure a web page graphic to expire after a very long period of time or a software download to only last for 24 hours.
For a publicly accessible data object (file), does this mean that the data object (file) itself will not be valid anymore, or that the browser will simply re-cache the object after the expiration date. As in, will I lose my data after ten years if I set my expirations that long? Or if I set a download for 24 hours, is it gone/inaccessible past that?
What if I don't set an expiration date?
回答1:
I believe you are referring to the signed urls for private data stored on Amazon S3.
If files are publicly accessible they can be accessed with a simple url to the file:
eg http://s3.amazonaws.com/[bucket]/[key]
However, they can be set to private in which case you need to provide a signed url to access the file. This url is created using your public and secret keys, and its this url that has an expiry time. eg
http://[bucket].s3.amazonaws.com/[key]?AWSAccessKeyId=[AWS_Public_Key]&Expires=1294766482&Signature=[generated_hash]
As per your question, for web graphics, you might re-use the same generated url with the expiry time set far into the future so that browsers can cache the file, whereas for file downloads you'd probably create a new url for each request with the url set to expire only a day in advance to protect your data.
This DOES NOT expire/delete/remove your data stored on S3. It only affects the url to the file and you can generate as many urls with different expiry dates as you require.
来源：https://stackoverflow.com/questions/4643328/amazon-s3-expiration-date