Send HTTP PURGE to caching servers on content publishing events
Project description
bethel.silva.purge
Introduction
This package is a wrapper around plone.cachepurging, providing purge support for for Silva content. Purges of Silva content are triggered when that content is changed or published.
Many Silva sites sit behind a caching proxy server (e.g. varnish, squid, pound, etc). The cache server will cache Silva content until it expires. For the most part this is positive and a good thing, so long as the caching headers are set correctly in Silva.
There becomes a problem, however, when a cached page is republished or closed. The caching server will continue to serve the cached page until it expires, even though there is newer content in Silva. The old content on the caching server is referred to as ‘stale’.
This extension adds a PurgingService to the Silva root. This service has options to enable purging, specifying the caching servers, and configuring plone.cachepurging-style simple virtualhosting (renamed to domain translations). There is also support for complex virtualhost situations, where many virtualhosts are served from different areas of a single Silva root (this is called path translations).
The actual PURGE requests occur AFTER the request is finished, via a ZPublisher.pubevents.PubSuccess event. Each PURGE path is put into a queue and multiple worker threads operate on the queue until empty. This is a sweet feature of plone.cachepurging, as it does not slow down the response to the client.
Note: while installing and configuring this extension is easy, do you homework! Read through the plone.cachepurging documentation and make sure you understand the fundamentals of PURGE.
Operation in Silva
When content is modified or published in Silva, a Purge event is triggered.
On modification
This package markes SilvaObject with the IPurgeable interface. This enables purging on IObjectMovedEvent and IObjectModifiedEvent. This ought to include containers (e.g. saving a container’s metadata). FMI see: purging objects automatically
If the object event is for an index document, the container is also purged.
On Publish
IVersions have an IPublishingEvent subscriber, which is triggered on every publishing event (publish, approval requesting, expires, approved, etc). While this will cause PURGEs to occur on events which to not affect the published version, the only effect is that the content is purged and needs to be re-fetched.
This causes a Purge of the IContent object, NOT the IVersion object, since the version isn’t cached.
If the object event is for an index document, the container is also purged.
What PURGE urls are generated?
Multiple PURGE urls are generated for each event. The following illustrates the paths generated BEFORE being translated by domain or path.
Object Events
Standard plone.cachepurging path: the full rooted path to object. For publishable content, this would be the path to the version, e.g.
/silva/example.com/doc/1.
[with path translations enabled] Index objects will add paths for the container, both with and without a trailing slash. e.g. for an event on /silva/example.com/folder/index:
/silva/example.com/folder /silva/example.com/folder/
[with domain translations enabled] The path relative to the silva root. e.g. for /silva/folder/doc:
/folder/doc
Publishing Events
Standard plone.cachepurging path: the full rooted path to object. For publishable content, this would be the path to the version, e.g.:
/silva/example.com/doc/1
[with path translations enabled] Path to IContent, e.g.:
/silva/example.com/doc
[with path translations enabled] Index objects will add paths for the container, both with and without a trailing slash. e.g. for an event on /silva/example.com/folder/index:
/silva/example.com/folder /silva/example.com/folder/
[with domain translations enabled] The path relative to the silva root. e.g. for /silva/folder/doc:
/folder/doc
Installation
To install the service, activate the “Silva Purging Service’ extension in the service_extensions. Installing this extension installs a plone.registry into the silva root and registers it as a local utility. The registry is used by plone.cachepurging to store it’s configuration.
Configuration
The service is configured via a ZMI management screen. Configuration will change the plone.registry settings for plone.cachepurging, and configure the path translations for complex vhosting.
1. Enable the service
This field represents the value of plone.cachepurging.interfaces.ICacheSettings.enabled.
Checking this will enable cache purging.
2. Set Cache Proxies
All frontend caching servers need to be added to this field. The format for each is a URI, e.g. http://cachingserver.example.com:6081
3. Complex Virtual Hosting (a.k.a. Path Translations)
Some Silva installations may serve multiple domains from within a single Silva root. These domains may be located underneath the Silva root, e.g. /silva_root/domain1, /silva_root/domain2, etc. When this is the case, plone.cachepurging vhosting support is not sufficient. Path Translations need to be used instead.
A path translation is simply an rule on how to translate a rooted path into a virtualhosting string.
To enable complex vhosting, check the “use path translations” field.
Configure the path translations by adding them one per line. The format for each line is the “rooted path + ‘ ‘ + translated path”. As an example, let’s say there is a vhost at /silva/example.com/. This is accessed from the domain http://example.com. The line for this path translation would then be:
/silva/example.com /VirtualHostBase/http/example.com:80/silva/www/VirtualHostRoot
Path Translations support multiple vhosts to the same root. If www.example.com also points /silva/example.com, an additional line can be added:
/silva/example.com /VirtualHostBase/http/www.example.com:80/silva/www/VirtualHostRoot
Additionally https vhosts can be supplied:
/silva/example.com /VirtualHostBase/https/www.example.com:443/silva/www/VirtualHostRoot
Support for inside-out hosting (using _vh_ segments) is supported, and in fact any string can be supplied as the “translated path”. The critical thing here is that the path generated match the path cached by the caching server, or no content will be purged.
When purging urls are being generated, any matching paths will have the matching part replaced with the vhost string, for all matches. The search for matchingpaths begins with the full path to the object then proceeds down the path, removing the last path component on each pass.
4. Domain Translations
Configures plone.cachepurging virtual host support. This package includes two types of virtual hosting support, so the plone.cachepurging style is renamed to ‘domain translations’. This approach rewrites the path from the silva root to a virtual hosting url.
To enable, check “Use domain translations”, and add the domains in the “Domains” field.
For more information on how this type of virtualhost works, see the plone.cachepurging documentation.
bethel.silva.purge changes
bethel.silva.purge 1.0b (2012-05-29)
initial release for bethel.silva.purge
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