Learn how continuous deployment works
The following topics explain how CloudFront continuous deployment works.
Topics
Route requests to the staging distribution
When you use CloudFront continuous deployment, you don't need to change anything about the viewer requests. Viewers cannot send requests directly to a staging distribution using a DNS name, IP address, or CNAME. Instead, viewers send requests to the primary (production) distribution, and CloudFront routes some of those requests to the staging distribution based on the traffic configuration settings in the continuous deployment policy. There are two types of traffic configurations:
- Weight-based
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A weight-based configuration routes the specified percentage of viewer requests to the staging distribution. When you use a weight-based configuration, you can also enable session stickiness, which helps make sure that CloudFront treats requests from the same viewer as part of a single session. For more information, see Session stickiness for weight-based configurations.
- Header-based
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A header-based configuration routes requests to the staging distribution when the viewer request contains a specific HTTP header (you specify the header and the value). Requests that don't contain the specified header and value are routed to the primary distribution. This configuration is useful for local testing, or when you have control over the viewer requests.
Note
Headers routed to your staging distribution must contain the prefix
aws-cf-cd-.
Session stickiness for weight-based configurations
When you use a weight-based configuration to route traffic to a staging distribution, you can also enable session stickiness, which helps make sure that CloudFront treats requests from the same viewer as a single session. When you enable session stickiness, CloudFront sets a cookie so that all requests from the same viewer in a single session are served by one distribution, either the primary or staging.
When you enable session stickiness, you can also specify the idle duration. If the viewer is idle (sends no requests) for this amount of time, the session expires and CloudFront treats future requests from this viewer as a new session. You specify the idle duration as a number of seconds, from 300 (five minutes) to 3600 (one hour).
In the following cases, CloudFront resets all sessions (even active ones) and considers all requests to be a new session:
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You disable or enable the continuous deployment policy
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You disable or enable the session stickiness setting
Update primary and staging distributions
When a primary distribution has an attached continuous deployment policy, the following configuration changes are available for both primary and staging distributions:
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All cache behavior settings, including the default cache behavior
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All origin settings (origins and origin groups)
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Custom error responses (error pages)
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Geographic restrictions
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Default root object
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Logging settings
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Description (comment)
You can also update external resources that are referenced in a distribution's configuration—such as a cache policy, a response headers policy, a CloudFront function, or a Lambda@Edge function.
Primary and staging distributions don't share a cache
The primary and staging distributions don't share a cache. When CloudFront sends the first request to a staging distribution, its cache is empty. As requests arrive at the staging distribution, it begins caching responses (if configured to do so).