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ActionEmbedding
- 1. ActionEmbedding Phil Cowans - LRUG, July 2010
- 4. Characteristics Of Pagelets Substantial content. Independence from the containing page. Potential to be handled by a back-end service. Can typically be cached. Localisation.
- 5. Why Think About Pages This Way? Helps define a ubiquitous language. Clean code: separation of responsibilities. Code reuse. Scalability.
- 6. Existing Tools / Patterns / Work Rails: ActionController::Components in early versions of Rails - dropped for performance reasons. Cells - plugin implementing similar functionality. Embedded Actions - another plugin. Elsewhere: Kohana - PHP framework based on Hierarchical Model-View-Controller (HMVC) pattern. Facebook BigPipe framework - Javascript tricks to get as much of the page to render as quickly as possible.
- 7. Why Start Again? An excuse to dig around inside of Rails. Experiment with various techniques for composing content. Make it easy for pagelet infrastructure to grow with the application: Easy to start using pagelets without complex infrastructure. Confidence that it will be possible to swap in more sophisticated embedding mechanisms without a rewrite. A couple of niggles with existing work: Wanted to reuse ActionController::Base for pagelets, rather than defining a new class. Use paths/URLs internally rather than controller/action/params.
- 8. HMVC Pagelet render handled by secondary internal request. Secondary request handled by standard Rails Controller / View (you can hit it directly if you want).
- 9. Request Forwarding Primary application forwards request to back end server Separate tier scales independently. Useful tricks: time out slow back end requests, silently drop pagelet on exception, easy killswitch for feature if necessary. Use appropriate mix of technologies - back end doesn't need to use same framework as front end, e.g. Sinatra for simple things.
- 10. Edge Side Includes Page composition handled by a proxy server. Works with proxies which support Edge Side Includes (e.g. Varnish)
- 11. XHR Composition Pagelets are loaded via secondary XHR requests in JavaScript.
- 12. Other Options (not yet implemented) Parallel execution. Potential to scale out for latency. BigPipe style composition.
- 13. Internals HMVC requests use Rack internally. Easy on Rails 2.3, as routing and controller speak Rack natively - can just inject request into later parts of standard processing pipeline. Rails 2.2 support (needed for SK) - backport bits of 2.3 to push Rack requests into controller.
- 14. Practical Experience Songkick activity feeds use ActionEmbedding / HMVC since Thursday. Measurable but relatively insignificant overhead - still room for improvement. Stable so far...
- 15. Issues / Todos Try XHR embedding in production. Better exception handling (right now you get the error embedded in the pagelet - should interpret response code). Consistent approach to constructing nested requests: Headers Access to cookies Security / access control. Investigate patterns for configuring pagelets.