I’m working on integrating some of Amazon’s Web Services into out eCommerce platform. I’ve been working on performance enhancements on and off for the last year and content delivery is the last big step for us. Getting started on S3 and CloudFront was pretty easy, but I ran into some issues when updating content in our S3 buckets. Luckily, Amazon added the ability to do this at the end of August. Since we use ASP.NET, I’ve started to work with their .NET SDK. Turns out, its pretty easy to invalidate some content.

public bool InvalidateContent(string distributionId, List<string> files)
{
    AmazonCloudFrontClient client = new AmazonCloudFrontClient(Settings.AWSAccessKey, Settings.AWSSecretKey);

    PostInvalidationRequest request = new PostInvalidationRequest();
    InvalidationBatch batch = new InvalidationBatch();

    batch.Paths = files;
    batch.CallerReference = GetHttpDate();

    request.InvalidationBatch = batch;
    request.DistributionId = distributionId;

    PostInvalidationResponse response = client.PostInvalidation(request);
    if (!String.IsNullOrEmpty(response.RequestId))
    {
	bool bInProgress = true;
	while (bInProgress)
	{
	    GetInvalidationRequest getReq = new GetInvalidationRequest();
	    getReq.DistributionId = distributionId;
	    getReq.InvalidationId = response.Id;

	    GetInvalidationResponse getRes = client.GetInvalidation(getReq);
	    bInProgress = getRes.Status.Equals("InProgress");

	    if (bInProgress)
	    {
		Thread.Sleep(Settings.AmazonWaitTime);
	    }
	}
    }
    else
    {
	return false;
    }

    return true;
}

InvalidateContent expects a CloudFront Distribution ID and a list of S3 files to invalidate. References to the static Settings class is just a class that reads in configuration settings from a configuration file, be it App.config or any configuration file you wish to set up. Basic values to store are your AWS Access Key, AWS Settings Key, and a wait time value before requesting information from Amazon again. There is also a method GetHttpDate(), which just returns:

System.DateTime.UtcNow.ToString("ddd, dd MMM yyyy HH:mm:ss ", System.Globalization.CultureInfo.InvariantCulture) + "GMT";

InvalidateContent() will make a PostInvalidationRequest (which is part of the ASP.NET AWS SDK) through an AmazonCloudFrontClient object. If this request is successfully posted, Amazon will return you a RequestId value that you can use to poll for the completion of your request. Keep in mind that you can only invalidate 1,000 S3 objects a month. After that Amazon will start to charge you $0.005 per object invalidated. This is per file, not per invalidation request. Hopefully you found this helpful!