Configuring Dispatcher configuring-dispatcher

The following sections describe how to configure various aspects of the Dispatcher.

Support for IPv4 and IPv6 support-for-ipv-and-ipv

All elements of AEM and Dispatcher can be installed in both IPv4 and IPv6 networks. See IPV4 and IPV6.

Dispatcher Configuration Files dispatcher-configuration-files

By default the Dispatcher configuration is stored in the dispatcher.any text file, though you can change the name and location of this file during installation.

The configuration file contains a series of single-valued or multi-valued properties that control the behavior of the Dispatcher:

An example configuration is structured as follows:

# name of the dispatcher
/name "internet-server"

# each farm configures a set off (loadbalanced) renders
/farms
 {
  # first farm entry (label is not important, just for your convenience)
   /website
     {
     /clientheaders
       {
       # List of headers that are passed on
       }
     /virtualhosts
       {
       # List of URLs for this Web site
       }
     /sessionmanagement
       {
       # settings for user authentification
       }
     /renders
       {
       # List of AEM instances that render the documents
       }
     /filter
       {
       # List of filters
       }
     /vanity_urls
       {
       # List of vanity URLs
       }
     /cache
       {
       # Cache configuration
       /rules
         {
         # List of cachable documents
         }
       /invalidate
         {
         # List of auto-invalidated documents
         }
       }
     /statistics
       {
       /categories
         {
         # The document categories that are used for load balancing estimates
         }
       }
     /stickyConnectionsFor "/myFolder"
     /health_check
       {
       # Page gets contacted when an instance returns a 500
       }
     /retryDelay "1"
     /numberOfRetries "5"
     /unavailablePenalty "1"
     /failover "1"
     }
 }

You can include other files that contribute to the configuration:

For example, to include the file myFarm.any in the /farms configuration use the following code:

/farms
  {
  $include "myFarm.any"
  }

To specify a range of files to include, use the asterisk (*) as a wildcard.

For example, if the files farm_1.any through to farm_5.any contain the configuration of farms one to five, you can include them as follows:

/farms
  {
  $include "farm_*.any"
  }

Using Environment Variables using-environment-variables

You can use environment variables in string-valued properties in the dispatcher.any file instead of hard-coding the values. To include the value of an environment variable, use the format ${variable_name}.

For example, if the dispatcher.any file is in the same directory as the cache directory, the following value for the docroot property can be used:

/docroot "${PWD}/cache"

As another example, if you create an environment variable named PUBLISH_IP that stores the hostname of the AEM publish instance, the following configuration of the /renders property can be used:

/renders {
  /0001 {
    /hostname "${PUBLISH_IP}"
    /port "8443"
  }
}

Naming the Dispatcher Instance naming-the-dispatcher-instance-name

Use the /name property to specify a unique name to identify your Dispatcher instance. The /name property is a top-level property in the configuration structure.

Defining Farms defining-farms-farms

The /farms property defines one or more sets of Dispatcher behaviors, where each set is associated with different web sites or URLs. The /farms property can include a single farm or multiple farms:

The /farms property is a top-level property in the configuration structure. To define a farm, add a child property to the /farms property. Use a property name that uniquely identifies the farm within the Dispatcher instance.

The /farmname property is multi-valued, and contains other properties that define Dispatcher behavior:

The value can include any alphanumeric (a-z, 0-9) character. The following example shows the skeleton definition for two farms named /daycom and /docsdaycom:

#name of dispatcher
/name "day sites"

#farms section defines a list of farms or sites
/farms
{
   /daycom
   {
       ...
   }
   /docdaycom
   {
      ...
   }
}

Each farm property can contain the following child properties:

Specify a Default Page (IIS Only) - /homepage specify-a-default-page-iis-only-homepage

Specifying the HTTP Headers to Pass Through specifying-the-http-headers-to-pass-through-clientheaders

The /clientheaders property defines a list of HTTP headers that Dispatcher passes from the client HTTP request to the renderer (AEM instance).

By default, the Dispatcher forwards the standard HTTP headers to the AEM instance. In some instances, you might want to forward additional headers, or remove specific headers:

If you customize the set of headers to pass through, you must specify an exhaustive list of headers, including those headers that are normally included by default.

For example, a Dispatcher instance that handles page activation requests for publish instances requires the PATH header in the /clientheaders section. The PATH header enables communication between the replication agent and the Dispatcher.

The following code is an example configuration for /clientheaders:

/clientheaders
  {
  "CSRF-Token"
  "X-Forwarded-Proto"
  "referer"
  "user-agent"
  "authorization"
  "from"
  "content-type"
  "content-length"
  "accept-charset"
  "accept-encoding"
  "accept-language"
  "accept"
  "host"
  "max-forwards"
  "proxy-authorization"
  "proxy-connection"
  "range"
  "cookie"
  "cq-action"
  "cq-handle"
  "handle"
  "action"
  "cqstats"
  "depth"
  "translate"
  "expires"
  "date"
  "dav"
  "ms-author-via"
  "if"
  "lock-token"
  "x-expected-entity-length"
  "destination"
  "PATH"
  }

Identifying Virtual Hosts identifying-virtual-hosts-virtualhosts

The /virtualhosts property defines a list of all hostname and URI combinations that Dispatcher accepts for this farm. You can use the asterisk (*) character as a wildcard. Values for the /virtualhosts property use the following format:

[scheme]host[uri][*]

The following example configuration handles requests for the .com and .ch domains of myCompany, and all domains of mySubDivision:

   /virtualhosts
    {
    "www.myCompany.com"
    "www.myCompany.ch"
    "www.mySubDivison.*"
    }

The following configuration handles all requests:

   /virtualhosts
    {
    "*"
    }

Resolving the Virtual Host resolving-the-virtual-host

When Dispatcher receives an HTTP or HTTPS request, it finds the virtual host value that best-matches the host, uri, and scheme headers of the request. Dispatcher evaluates the values in the virtualhosts properties in the following order:

Dispatcher finds the best-matching virtual host value in the following manner:

Therefore, you should place your default virtual host at the top of the virtualhosts property. PLace it in the topmost farm of your dispatcher.any file.

Example Virtual Host Resolution example-virtual-host-resolution

The following example represents a snippet from a dispatcher.any file that defines two Dispatcher farms, and each farm defines a virtualhosts property.

/farms
  {
  /myProducts
    {
    /virtualhosts
      {
      "www.mycompany.com/products/*"
      }
    /renders
      {
      /hostname "server1.myCompany.com"
      /port "80"
      }
    }
  /myCompany
    {
    /virtualhosts
      {
      "www.mycompany.com"
      }
    /renders
      {
      /hostname "server2.myCompany.com"
      /port "80"
      }
    }
  }

Using this example, the following table shows the virtual hosts that are resolved for the given HTTP requests:

Enabling Secure Sessions - /sessionmanagement enabling-secure-sessions-sessionmanagement

Create a secure session for access to the render farm so that users must log in to access any page in the farm. After logging in, users can access pages in the farm. See Creating a Closed User Group for information about using this feature with CUGs. Also, see the Dispatcher Security Checklist before going live.

The /sessionmanagement property is a subproperty of /farms.

/sessionmanagement has several subparameters:

/directory (mandatory)

The directory that stores the session information. If the directory does not exist, it is created.

/sessionmanagement
  {
  /directory "/usr/local/apache/.sessions"
  }

/encode (optional)

How the session information is encoded. Use md5 for encryption using the md5 algorithm, or hex for hexadecimal encoding. If you encrypt the session data, a user with access to the file system cannot read the session contents. The default is md5.

/header (optional)

The name of the HTTP header or cookie that stores the authorization information. If you store the information in the http header, use HTTP:<header-name>. To store the information in a cookie, use Cookie:<header-name>. If you do not specify a value, HTTP:authorization is used.

/timeout (optional)

The number of seconds until the session times out after it has been used last. If not specified "800" is used, so the session times out a little over 13 minutes after the last request of the user.

An example configuration looks as follows:

/sessionmanagement
  {
  /directory "/usr/local/apache/.sessions"
  /encode "md5"
  /header "HTTP:authorization"
  /timeout "800"
  }

Defining Page Renderers defining-page-renderers-renders

The /renders property defines the URL to which the Dispatcher sends requests to render a document. The following example /renders section identifies a single AEM instance for rendering:

/renders
  {
    /myRenderer
      {
      # hostname or IP of the renderer
      /hostname "aem.myCompany.com"
      # port of the renderer
      /port "4503"
      # connection timeout in milliseconds, "0" (default) waits indefinitely
      /timeout "0"
      }
  }

The following example /renders section identifies an AEM instance that runs on the same computer as Dispatcher:

/renders
  {
    /myRenderer
     {
     /hostname "127.0.0.1"
     /port "4503"
     }
  }

The following example /renders section distributes render requests equally among two AEM instances:

/renders
  {
    /myFirstRenderer
      {
      /hostname "aem.myCompany.com"
      /port "4503"
      }
    /mySecondRenderer
      {
      /hostname "127.0.0.1"
      /port "4503"
      }
  }

Renders options renders-options

/timeout

Specifies the connection timeout accessing the AEM instance in milliseconds. The default is "0", causing the Dispatcher to wait indefinitely.

/receiveTimeout

Specifies the time in milliseconds that a response is allowed to take. The default is "600000", causing Dispatcher to wait for 10 Minutes. A setting of "0" eliminates the timeout.

If the timeout is reached while parsing response headers, an HTTP Status of 504 (Bad Gateway) is returned. If the timeout is reached while the response body is read, the Dispatcher returns the incomplete response to the client. It also deletes any cached files that might have been written.

/ipv4

Specifies whether Dispatcher uses the getaddrinfo function (for IPv6) or the gethostbyname function (for IPv4) for obtaining the IP address of the render. A value of 0 causes getaddrinfo to be used. A value of 1 causes gethostbyname to be used. The default value is 0.

The getaddrinfo function returns a list of IP addresses. Dispatcher iterates the list of addresses until it establishes a TCP/IP connection. Therefore, the ipv4 property is important when the render hostname is associated with multiple IP addresses. And, the host, in response to the getaddrinfo function, returns a list of IP addresses that are always in the same order. In this situation, you should use the gethostbyname function so that the IP address that Dispatcher connects with is randomized.

Amazon Elastic Load Balancing (ELB) is such a service that responds to getaddrinfo with a potentially same-ordered list of IP addresses.

/secure

If the /secure property has a value of "1", Dispatcher uses HTTPS to communicate with the AEM instance. For more details, see Configuring Dispatcher to Use SSL.

/always-resolve

With Dispatcher version 4.1.6, you can configure the /always-resolve property as follows:

Also, this property can be used in case you run into dynamic IP resolution issues, as shown in the following sample:

/renders {
  /0001 {
     /hostname "host-name-here"
     /port "4502"
     /ipv4 "1"
     /always-resolve "1"
     }
  }

Configuring Access to Content configuring-access-to-content-filter

Use the /filter section to specify the HTTP requests that Dispatcher accepts. All other requests are sent back to the web server with a 404 error code (page not found). If no /filter section exists, all requests are accepted.

Note: Requests for the statfile are always rejected.

The /filter section consists of a series of rules that either deny or allow access to content according to patterns in the request-line part of the HTTP request. Use an allowlist strategy for your /filter section:

Defining a Filter defining-a-filter

Each item in the /filter section includes a type and a pattern that is matched with a specific element of the request line or the entire request line. Each filter can contain the following items:

The request-line Part of HTTP Requests the-request-line-part-of-http-requests

HTTP/1.1 defines the request-line as follows:

Method Request-URI HTTP-Version<CRLF>

The <CRLF> characters represent a carriage return followed by a line feed. The following example is the request-line that is received when a client requests the US-English page of the WKND site:

GET /content/wknd/us/en.html HTTP.1.1<CRLF>

Your patterns must account for the space characters in the request-line and the <CRLF> characters.

Double-quotes vs Single-quotes double-quotes-vs-single-quotes

When creating your filter rules, use double quotation marks "pattern" for simple patterns. If you are using Dispatcher 4.2.0 or later and your pattern includes a regular expression, you must enclose the regex pattern '(pattern1|pattern2)' within single quotation marks.

Regular Expressions regular-expressions

In Dispatcher versions later than 4.2.0, you can include POSIX Extended Regular Expressions in your filter patterns.

Troubleshooting Filters troubleshooting-filters

If your filters are not triggering in the way you would expect, enable Trace Logging on Dispatcher so you can see which filter is intercepting the request.

Example Filter: Deny All example-filter-deny-all

The following example filter section causes the Dispatcher to deny requests for all files. Deny access to all files and then allow access to specific areas.

/0001  { /type "deny" /url "*"  }

Requests to an explicitly denied area result in a 404 error code (page not found) being returned.

Example Filter: Deny Access to Specific Areas example-filter-deny-access-to-specific-areas

Filters also let you deny access to various elements, for example, ASP pages and sensitive areas within a publish instance. The following filter denies access to ASP pages:

/0002  { /type "deny" /url "*.asp"  }

Example Filter: Enable POST Requests example-filter-enable-post-requests

The following example filter allows submitting form data by the POST method:

/filter {
    /0001  { /glob "*" /type "deny" }
    /0002 { /type "allow" /method "POST" /url "/content/[.]*.form.html" }
}

Example Filter: Allow Access to the Workflow Console example-filter-allow-access-to-the-workflow-console

The following example shows a filter used to allow external access to the Workflow console:

/filter {
    /0001  { /glob "*" /type "deny" }
    /0002  {  /type "allow"  /url "/libs/cq/workflow/content/console*"  }
}

If your publish instance uses a web application context (for example publish), it can also be added to your filter definition.

/0003   { /type "deny"  /url "/publish/libs/cq/workflow/content/console/archive*"  }

If you must access single pages within the restricted area, you can allow access to them. For example, to allow access to the Archive tab within the Workflow console, add the following section:

/0004  { /type "allow"  /url "/libs/cq/workflow/content/console/archive*"   }

Example filter: Using Regular Expressions example-filter-using-regular-expressions

This filter enables extensions in non-public content directories using a regular expression, defined here between single quotes:

/005  {  /type "allow" /extension '(css|gif|ico|js|png|swf|jpe?g)' }

Example filter: Filter extra Elements of a Request URL example-filter-filter-additional-elements-of-a-request-url

Below is a rule example that blocks content grabbing from the /content path and its subtree, using filters for path, selectors, and extensions:

/006 {
        /type "deny"
        /path "/content/*"
        /selectors '(feed|rss|pages|languages|blueprint|infinity|tidy|sysview|docview|query|jcr:content|_jcr_content|search|childrenlist|ext|assets|assetsearch|[0-9-]+)'
        /extension '(json|xml|html|feed))'
        }

Example /filter section example-filter-section

When configuring the Dispatcher, restrict external access as much as possible. The following example provides minimal access for external visitors:

After you create filters, test page access to ensure that your AEM instance is secure.

The following /filter section of the dispatcher.any file can be used as a basis in your Dispatcher configuration file.

This example is based on the default configuration file that is provided with Dispatcher and is intended as an example for use in a production environment. Items prefixed with # are deactivated (commented out). Care should be taken if you decide to activate any of these items (by removing the # on that line). Doing so can have a security impact.

Deny access to everything, then allow access to specific (limited) elements:

  /filter
      {
      # Deny everything first and then allow specific entries
      /0001  { /type "deny" /url "*"  }

      # Open consoles
#     /0011 { /type "allow" /url "/admin/*"  }  # allow servlet engine admin
#     /0012 { /type "allow" /url "/crx/*"    }  # allow content repository
#     /0013 { /type "allow" /url "/system/*" }  # allow OSGi console

      # Allow non-public content directories
#     /0021 { /type "allow" /url "/apps/*"   }  # allow apps access
#     /0022 { /type "allow" /url "/bin/*"    }
      /0023 { /type "allow" /url "/content*" }  # disable this rule to allow mapped content only

#     /0024 { /type "allow" /url "/libs/*"   }
#     /0025 { /type "deny"  /url "/libs/shindig/proxy*" } # if you enable /libs close access to proxy

#     /0026 { /type "allow" /url "/home/*"   }
#     /0027 { /type "allow" /url "/tmp/*"    }
#     /0028 { /type "allow" /url "/var/*"    }

      # Enable extensions in non-public content directories, using a regular expression
      /0041
        {
        /type "allow"
        /extension '(css|gif|ico|js|png|swf|jpe?g)'
        }

      # Enable features
      /0062 { /type "allow" /url "/libs/cq/personalization/*"  }  # enable personalization

      # Deny content grabbing, on all accessible pages, using regular expressions
      /0081
        {
        /type "deny"
        /selectors '((sys|doc)view|query|[0-9-]+)'
        /extension '(json|xml)'
        }
      # Deny content grabbing for /content and its subtree
      /0082
        {
        /type "deny"
        /path "/content/*"
        /selectors '(feed|rss|pages|languages|blueprint|infinity|tidy)'
        /extension '(json|xml|html)'
        }

#     /0087 { /type "allow" /method "GET" /extension 'json' "*.1.json" }  # allow one-level json requests
}

Consider the following recommendations if you do choose to extend access:

Depending on your installation, there might be more resources under /libs, /apps or elsewhere, that must be made available. You can use the access.log file as one method of determining resources that are being accessed externally.

Restricting Query Strings restricting-query-strings

Since Dispatcher version 4.1.5, use the /filter section to restrict query strings. It is recommended that you explicitly allow query strings and exclude generic allowance through allow filter elements.

A single entry can have either glob or some combination of method, url, query, and version, but not both. The following example allows the a=* query string and denies all other query strings for URLs that resolve to the /etc node:

/filter {
 /0001 { /type "deny" /method "POST" /url "/etc/*" }
 /0002 { /type "allow" /method "GET" /url "/etc/*" /query "a=*" }
}

/filter {
>/0001 { /type "deny" /method "*" /url "/path/*" }
>/0002 { /type "allow" /method "GET" /url "/path/*" }
>/0003 { /type "deny" /method "GET" /url "/path/*" /query "*" }
>/0004 { /type "allow" /method "GET" /url "/path/*" /query "a=*" }
}

Testing Dispatcher Security testing-dispatcher-security

Dispatcher filters should block access to the following pages and scripts on AEM publish instances. Use a web browser to attempt to open the following pages as a site visitor would and verify that a code 404 is returned. If any other result is obtained, adjust your filters.

You should see normal page rendering for /content/add_valid_page.html?debug=layout.

To determine whether anonymous write access is enabled, issue the following command in a terminal or command prompt. Writing data to the node should not be possible.

curl -X POST "https://anonymous:anonymous@hostname:port/content/usergenerated/mytestnode"

To attempt to invalidate the Dispatcher cache and ensure that you receive a code 403 response, issue the following command in a terminal or command prompt:

curl -H "CQ-Handle: /content" -H "CQ-Path: /content" https://yourhostname/dispatcher/invalidate.cache

Enabling Access to Vanity URLs enabling-access-to-vanity-urls-vanity-urls

Configure the Dispatcher to enable access to vanity URLs that are configured for your AEM pages.

When access to vanity URLs is enabled, Dispatcher periodically calls a service that runs on the render instance to obtain a list of vanity URLs. Dispatcher stores this list in a local file. When a request for a page is denied due to a filter in the /filter section, Dispatcher consults the list of vanity URLs. If the denied URL is on the list, Dispatcher allows access to the vanity URL.

To enable access to vanity URLs, add a /vanity_urls section to the /farms section, similar to the following example:

 /vanity_urls {
      /url "/libs/granite/dispatcher/content/vanityUrls.html"
      /file "/tmp/vanity_urls"
      /delay 300
 }

The /vanity_urls section contains the following properties:

Use the following procedure to enable access to vanity URLs.

Forwarding Syndication Requests - /propagateSyndPost forwarding-syndication-requests-propagatesyndpost

Syndication requests are intended for Dispatcher only, so by default they are not sent to the renderer (for example, an AEM instance).

If necessary, set the /propagateSyndPost property to "1" to forward syndication requests to Dispatcher. If set, you must make sure that POST requests are not denied in the filter section.

Configuring the Dispatcher Cache - /cache configuring-the-dispatcher-cache-cache

The /cache section controls how Dispatcher caches documents. Configure several subproperties to implement your caching strategies:

An example cache section might look as follows:

/cache
  {
  /docroot "/opt/dispatcher/cache"
  /statfile  "/tmp/dispatcher-website.stat"
  /allowAuthorized "0"

  /rules
    {
    # List of files that are cached
    }

  /invalidate
    {
    # List of files that are auto-invalidated
    }
  }

Specifying the Cache Directory specifying-the-cache-directory

The /docroot property identifies the directory where cached files are stored.

If you use multiple farms, each farm must use a different document root.

Naming the Statfile naming-the-statfile

The /statfile property identifies the file to use as the statfile. Dispatcher uses this file to register the time of the most recent content update. The statfile can be any file on the web server.

The statfile has no content. When content is updated, the Dispatcher updates the timestamp. The default statfile is named .stat and is stored in the docroot. Dispatcher blocks access to the statfile.

Serving Stale Documents When Errors Occur serving-stale-documents-when-errors-occur

The /serveStaleOnError property controls whether Dispatcher returns invalidated documents when the render server returns an error. By default, when a statfile is touched and invalidates cached content, the Dispatcher deletes the cached content. This action is done the next time it is requested.

If /serveStaleOnError is set to "1", Dispatcher does not delete invalidated content from the cache. That is, unless the render server returns a successful response. A 5xx response from AEM or a connection timeout causes the Dispatcher to serve the outdated content and respond with and HTTP Status of 111 (Revalidation Failed).

Caching When Authentication is Used caching-when-authentication-is-used

The /allowAuthorized property controls whether requests that contain any of the following authentication information are cached:

By default, requests that include this authentication information are not cached because authentication is not performed when a cached document is returned to the client. This configuration prevents Dispatcher from serving cached documents to users who do not have the necessary rights.

However, if your requirements permit the caching of authenticated documents, set /allowAuthorized to one:

/allowAuthorized "1"

Specifying the Documents to Cache specifying-the-documents-to-cache

The /rules property controls which documents are cached according to the document path. Regardless of the /rules property, Dispatcher never caches a document in the following circumstances:

Each item in the /rules property includes a glob pattern and a type:

If you do not have dynamic pages (beyond those pages already excluded by the above rules), you can configure Dispatcher to cache everything. The rules section looks as follows:

/rules
  {
    /0000  {  /glob "*"   /type "allow" }
  }

For information about Glob properties, see Designing Patterns for Glob Properties.

If there are some sections of your page that are dynamic (for example a news application) or within a closed user group, you can define exceptions:

/rules
  {
   /0000  { /glob "*" /type "allow" }
   /0001  { /glob "/en/news/*" /type "deny" }
   /0002  { /glob "*/private/*" /type "deny"  }
  }

Compression

On Apache web servers, you can compress the cached documents. Compression allows Apache to return the document in a compressed form if so requested by the client. Compression is done automatically by enabling the Apache module mod_deflate, for example:

AddOutputFilterByType DEFLATE text/plain

The module is installed by default with Apache 2.x.

Invalidating Files by Folder Level invalidating-files-by-folder-level

Use the /statfileslevel property to invalidate cached files according to their path:

Only resources along the path to the invalidated file are affected. Consider the following example: a website uses the structure /content/myWebsite/xx/. If you set statfileslevel as 3, a .statfile is created as follows:

When a file in /content/myWebsite/xx is invalidated, then every .stat file from docroot down to /content/myWebsite/xxis touched. This scenario is the case only for /content/myWebsite/xx and not for example /content/myWebsite/yy or /content/anotherWebSite.

Automatically Invalidating Cached Files automatically-invalidating-cached-files

The /invalidate property defines the documents that are automatically invalidated when content is updated.

With automatic invalidation, Dispatcher does not delete cached files after a content update, but checks their validity when they are next requested. Documents in the cache that are not auto-invalidated remain in the cache until a content update explicitly deletes them.

Automatic invalidation is typically used for HTML pages. HTML pages often contain links to other pages, making it difficult to determine whether a content update affects a page. To make sure that all relevant pages are invalidated when content is updated, automatically invalidate all HTML pages. The following configuration invalidates all HTML pages:

  /invalidate
  {
   /0000  { /glob "*" /type "deny" }
   /0001  { /glob "*.html" /type "allow" }
  }

For information about Glob properties, see Designing Patterns for Glob Properties.

This configuration causes the following activity when /content/wknd/us/en is activated:

If you offer automatically generated PDF and ZIP files for download, you might have to invalidate these files automatically, too. A configuration example looks as follows:

/invalidate
  {
   /0000 { /glob "*" /type "deny" }
   /0001 { /glob "*.html" /type "allow" }
   /0002 { /glob "*.zip" /type "allow" }
   /0003 { /glob "*.pdf" /type "allow" }
  }

The AEM integration with Adobe Analytics delivers configuration data in an analytics.sitecatalyst.js file in your website. The example dispatcher.any file that is provided with Dispatcher includes the following invalidation rule for this file:

{
   /glob "*/analytics.sitecatalyst.js"  /type "allow"
}

Using custom invalidation scripts using-custom-invalidation-scripts

The /invalidateHandler property lets you define a script that is called for each invalidation request received by Dispatcher.

It is called with the following arguments:

This method can be used to cover several different use cases. For example, invalidating other application-specific caches, or to handle cases where the externalized URL of a page, and its place in the docroot, does not match the content path.

The following example script logs each invalidated request to a file.

/invalidateHandler "/opt/dispatcher/scripts/invalidate.sh"

Sample invalidation handler script sample-invalidation-handler-script

#!/bin/bash

printf "%-15s: %s %s" $1 $2 $3>> /opt/dispatcher/logs/invalidate.log

Limiting the Clients That Can Flush the Cache limiting-the-clients-that-can-flush-the-cache

The /allowedClients property defines specific clients that are allowed to flush the cache. The globbing patterns are matched against the IP.

The following example:

/allowedClients
  {
   /0001 { /glob "*.*.*.*"  /type "deny" }
   /0002 { /glob "127.0.0.1" /type "allow" }
  }

For information about Glob properties, see Designing Patterns for Glob Properties.

Ignoring URL Parameters ignoring-url-parameters

The ignoreUrlParams section defines which URL parameters are ignored when determining whether a page is cached or delivered from cache:

When a parameter is ignored for a page, the page is cached the first time that the page is requested. Subsequent requests for the page are served to the cached page, regardless of the value of the parameter in the request.

To specify which parameters are ignored, add glob rules to the ignoreUrlParams property:

The following example causes Dispatcher to ignore all parameters, except the nocache parameter. As such, Dispatcher never caches request URLs that include the nocache parameter:

/ignoreUrlParams
{
    # ignore-all-url-parameters-by-dispatcher-and-requests-are-cached
    /0001 { /glob "*" /type "allow" }
    # allow-the-url-parameter-nocache-to-bypass-dispatcher-on-every-request
    /0002 { /glob "nocache" /type "deny" }
}

In the context of the ignoreUrlParams configuration example above, the following HTTP request causes the page to be cached because the willbecached parameter is ignored:

GET /mypage.html?willbecached=true

In the context of the ignoreUrlParams configuration example, the following HTTP request causes the page not to be cached because the nocache parameter is not ignored:

GET /mypage.html?nocache=true
GET /mypage.html?nocache=true&willbecached=true

For information about Glob properties, see Designing Patterns for Glob Properties.

Caching HTTP Response Headers caching-http-response-headers

The /headers property lets you define the HTTP header types that Dispatcher is going to cache. On the first request to an uncached resource, all headers matching one of the configured values (see the configuration sample below) are stored in a separate file, next to the cache file. On subsequent requests to the cached resource, the stored headers are added to the response.

Below is a sample from the default configuration:

/cache {
  ...
  /headers {
    "Cache-Control"
    "Content-Disposition"
    "Content-Type"
    "Expires"
    "Last-Modified"
    "X-Content-Type-Options"
    "Last-Modified"
  }
}

FileETag none

Dispatcher Cache File Permissions dispatcher-cache-file-permissions

The mode property specifies what file permissions are applied to new directories and files in the cache. The umask of the calling process restricts this setting. It is an octal number constructed from the sum of one or more of the following values:

The default value is 0755, which allows the owner to read, write, or search and the group and others to read or search.

Throttling .stat file touching throttling-stat-file-touching

With the default /invalidate property, every activation effectively invalidates all .html files (when their path matches the /invalidate section). On a website with considerable traffic, multiple, subsequent activations increase the cpu load on the backend. In such a scenario, it is desirable to “throttle” .stat file touching to keep the website responsive. You can accomplish this action by using the /gracePeriod property.

The /gracePeriod property defines the number of seconds a stale, auto-invalidated resource may still be served from the cache after the last occurring activation. The property can be used in a setup where a batch of activations would otherwise repeatedly invalidate the entire cache. The recommended value is 2 seconds.

For more details, see /invalidate and /statfileslevelearlier.

Configuring Time Based Cache Invalidation - /enableTTL configuring-time-based-cache-invalidation-enablettl

Time-based cache invalidation depends on the /enableTTL property and the presence of regular expiration headers from the HTTP standard. If you set the property to 1 (/enableTTL "1"), it evaluates the response headers from the backend. If the headers contain a Cache-Control, max-age or Expires date, an auxiliary, empty file next to the cached file is created, with the modification time equal to the expiry date. When the cached file is requested past the modification time, it is automatically re-requested from the backend.

Before Dispatcher 4.3.5, the TTL invalidation logic was based only on the configured TTL value. With Dispatcher 4.3.5, both the set TTL and the Dispatcher cache invalidation rules are accounted for. As such, for a cached file:

This new implementation supports use cases where files have a longer TTL (for example, on the CDN). But those file can still be invalidated even if the TTL has not expired. It favors content freshness over cache-hit ratio on the Dispatcher.

Conversely, in case you need only the expiration logic applied to a file then set /enableTTL to 1 and exclude that file from the standard cache invalidation mechanism. For example, you can:

  /invalidate
  {
   /0000  { /glob "*" /type "deny" }
   /0001  { /glob "*.html" /type "allow" }
   /0002  { /glob "*.example.html" /type "deny" }
  }

Doing so ensures that .stat file invalidation is not used and only TTL expiration is active for the specified files.

Configuring Load Balancing - /statistics configuring-load-balancing-statistics

The /statistics section defines categories of files for which Dispatcher scores the responsiveness of each render. Dispatcher uses the scores to determine which render to send a request.

Each category that you create defines a glob pattern. Dispatcher compares the URI of the requested content to these patterns to determine the category of the requested content:

Dispatcher supports a maximum of eight statistics categories. If you define more than eight categories, only the first 8 are used.

Render Selection

Each time the Dispatcher requires a rendered page, it uses the following algorithm to select the render:

The score for a render’s category is based on previous response times, and previous failed and successful connections that Dispatcher attempts. For each attempt, the score for the category of the requested URI is updated.

Defining Statistics Categories defining-statistics-categories

Define a category for each type of document for which you want to keep statistics for render selection. The /statistics section contains a /categories section. To define a category, add a line below the /categories section that has the following format:

/name { /glob "pattern"}

The category name must be unique to the farm. The pattern is described in the Designing Patterns for glob Properties section.

To determine the category of a URI, the Dispatcher compares the URI with each category pattern until a match is found. Dispatcher begins with the first category in the list and continues in order. Therefore, place categories with more specific patterns first.

For example, Dispatcher the default dispatcher.any file defines an HTML category and an others category. The HTML category is more specific and so it appears first:

/statistics
  {
  /categories
    {
      /html { /glob "*.html" }
      /others  { /glob "*" }
    }
  }

The following example also includes a category for search pages:

/statistics
  {
  /categories
    {
      /search { /glob "*search.html" }
      /html { /glob "*.html" }
      /others  { /glob "*" }
    }
  }

Reflecting Server Unavailability in Dispatcher Statistics reflecting-server-unavailability-in-dispatcher-statistics

The /unavailablePenalty property sets the time (in tenths of a second) that is applied to the render statistics when a connection to the render fails. Dispatcher adds the time to the statistics category that matches the requested URI.

For example, the penalty is applied when the TCP/IP connection to the designated hostname/port cannot be established. The reason is either because AEM is not running (and not listening) or because of a network-related problem.

The /unavailablePenalty property is a direct child of the /farm section (a sibling of the /statistics section).

If no /unavailablePenalty property exists, a value of "1" is used.

/unavailablePenalty "1"

Identifying a Sticky Connection Folder - /stickyConnectionsFor identifying-a-sticky-connection-folder-stickyconnectionsfor

The /stickyConnectionsFor property defines one folder that contains sticky documents. This property is accessed using the URL. Dispatcher sends all requests, from a single user that are in this folder, to the same render instance. Sticky connections ensure that session data is present and consistent for all documents. This mechanism uses the renderid cookie.

The following example defines a sticky connection to the /products folder:

/stickyConnectionsFor "/products"

When a page is composed of content from several content nodes, include the /paths property that lists the paths to the content. For example, a page contains content from /content/image, /content/video, and /var/files/pdfs. The following configuration enables sticky connections for all content on the page:

/stickyConnections {
  /paths {
    "/content/image"
    "/content/video"
    "/var/files/pdfs"
  }
}

httpOnly httponly

When sticky connections are enabled, the Dispatcher module sets the renderid cookie. This cookie does not have the httponly flag, which should be added to enhance security. You add the httponly flag by setting the httpOnly property in the /stickyConnections node of a dispatcher.any configuration file. The property’s value (either 0 or 1) defines whether the renderid cookie has the HttpOnly attribute appended. The default value is 0, which means the attribute is not added.

For additional information about the httponly flag, read this page.

secure secure

When sticky connections are enabled, the Dispatcher module sets the renderid cookie. This cookie does not have the secure flag, which should be added to enhance security. You add the secure flag setting the secure property in the /stickyConnections node of a dispatcher.any configuration file. The property’s value (either 0 or 1) defines whether the renderid cookie has the secure attribute appended. The default value is 0, which means the attribute is added if the incoming request is secure. If the value is set to 1, then the secure flag is added regardless of whether the incoming request is secure or not.

Handling Render Connection Errors handling-render-connection-errors

Configure Dispatcher behavior when the render server returns a 500 error, or is unavailable.

Specifying a Health Check Page specifying-a-health-check-page

Use the /health_check property to specify a URL that is checked when a 500 status code occurs. If this page also returns a 500 status code, the instance is considered to be unavailable and a configurable time penalty ( /unavailablePenalty) is applied to the render before retrying.

/health_check
  {
  # Page gets contacted when an instance returns a 500
  /url "/health_check.html"
  }

Specifying the Page Retry Delay specifying-the-page-retry-delay

The /retryDelay property sets the time (in seconds) that Dispatcher waits between rounds of connection attempts with the farm renders. For each round, the maximum number of times the Dispatcher attempts a connection to a render is the number of renders in the farm.

Dispatcher uses a value of "1" if /retryDelay is not explicitly defined. The default value is usually appropriate.

/retryDelay "1"

Configuring the Number of Retries configuring-the-number-of-retries

The /numberOfRetries property sets the maximum number of rounds of connection attempts that Dispatcher performs with the renders. If Dispatcher cannot successfully connect to a render after this number of retries, Dispatcher returns a failed response.

For each round, the maximum number of times the Dispatcher attempts a connection to a render is the number of renders in the farm. Therefore, the maximum number of times that the Dispatcher attempts a connection is ( /numberOfRetries) x (the number of renders).

If the value is not explicitly defined, the default value is 5.

/numberOfRetries "5"

Using the Failover Mechanism using-the-failover-mechanism

To resend requests to different renders when the original request fails, enable the failover mechanism on your Dispatcher farm. When failover is enabled, Dispatcher has the following behavior:

To enable failover, add the following line to the farm (or website):

/failover "1"

Ignoring Interruption Errors - /ignoreEINTR ignoring-interruption-errors-ignoreeintr

Any file system-oriented system call can be interrupted EINTR if the object of the system call is on a remote system accessed by way of NFS. Whether these system calls can time out or be interrupted is based on how the underlying file system was mounted on the local machine.

Use the /ignoreEINTR parameter if your instance has such a configuration and the log contains the following message:

Error while reading response: Interrupted system call

Internally, Dispatcher reads the response from the remote server (that is, AEM) using a loop that can be represented as:

while (response not finished) {
read more data
}

Such messages can be generated when the EINTR occurs in the read more data section. And, the reception of a signal before any data was received is the cause.

To ignore such interrupts, you can add the following parameter to dispatcher.any (before /farms):

/ignoreEINTR "1"

Setting /ignoreEINTR to "1" causes Dispatcher to continue to attempt to read data until the complete response is read. The default value is 0 and deactivates the option.

Designing Patterns for Glob Properties designing-patterns-for-glob-properties

Several sections in the Dispatcher configuration file use the glob properties as selection criteria for client requests. The values of glob properties are patterns that Dispatcher compares to an aspect of the request, such as the path of the requested resource, or the IP address of the client. For example, the items in the /filter section use glob patterns to identify the paths of the pages that Dispatcher acts on or rejects.

The glob values can include wildcard characters and alphanumeric characters to define the pattern.

Logging logging

In the Web server configuration, you can set:

Refer to the web server documentation and the readme file of your Dispatcher instance for more information.

Apache Rotated or Piped Logs

If using an Apache web server, you can use the standard functionality for Log Rotations, or Piped Logs, or both. For example, using Piped Logs:

DispatcherLog "| /usr/apache/bin/rotatelogs logs/dispatcher.log%Y%m%d 604800"

This functionality automatically rotates:

See the Apache Web Server documentation on Log Rotation and Piped Logs. For example, Apache 2.4.

Trace Logging trace-logging

Among other enhancements for the Dispatcher, version 4.2.0 also introduces Trace Logging.

This ability is a higher level than Debug logging that shows additional information in the logs. It adds logging for:

You can enable Trace Logging by setting the log level to 4 in your web server.

Below is an example of logs with tracing enabled:

[Thu Mar 03 16:05:38 2016] [T] [17183] request.headers[Host] = "localhost:8443"
[Thu Mar 03 16:05:38 2016] [T] [17183] request.headers[User-Agent] = "curl/7.43.0"
[Thu Mar 03 16:05:38 2016] [T] [17183] request.headers[Accept] = "*/*"
[Thu Mar 03 16:05:38 2016] [T] [17183] request.headers[X-Forwarded-SSL-Client-Cert] = "(null)"
[Thu Mar 03 16:05:38 2016] [T] [17183] request.headers[Via] = "1.1 localhost:8443 (dispatcher)"
[Thu Mar 03 16:05:38 2016] [T] [17183] request.headers[X-Forwarded-For] = "::1"
[Thu Mar 03 16:05:38 2016] [T] [17183] request.headers[X-Forwarded-SSL] = "on"
[Thu Mar 03 16:05:38 2016] [T] [17183] request.headers[X-Forwarded-SSL-Cipher] = "DHE-RSA-AES256-SHA"
[Thu Mar 03 16:05:38 2016] [T] [17183] request.headers[X-Forwarded-SSL-Session-ID] = "ba931f5e4925c2dde572d766fdd436375e15a0fd24577b91f4a4d51232a934ae"
[Thu Mar 03 16:05:38 2016] [T] [17183] request.headers[X-Forwarded-Port] = "8443"
[Thu Mar 03 16:05:38 2016] [T] [17183] request.headers[Server-Agent] = "Communique-Dispatcher"

And an event is logged when a file that matches a blocking rule is requested:

[Thu Mar 03 14:42:45 2016] [T] [11831] 'GET /content.infinity.json HTTP/1.1' was blocked because of /0082

Confirming Basic Operation confirming-basic-operation

To confirm basic operation and interaction of the web server, Dispatcher and AEM instance you can use the following steps:

Using Multiple Dispatchers using-multiple-dispatchers

In complex setups, you may use multiple Dispatchers. For example, you may use:

In such a case, make sure that each request goes through only one Dispatcher. A Dispatcher does not handle requests that come from another Dispatcher. Therefore, make sure that both Dispatchers access the AEM website directly.

Debugging debugging

When adding the header X-Dispatcher-Info to a request, Dispatcher answers whether the target was cached, returned from cached, or not cacheable at all. The response header X-Cache-Info contains this information in a readable form. You can use these response headers to debug issues involving responses cached by the Dispatcher.

This functionality is not enabled by default, so for the response header X-Cache-Info to be included, the farm must contain the following entry:

/info "1"

For example,

/farm
{
    /mywebsite
    {
        # Include X-Cache-Info response header if X-Dispatcher-Info is in request header
        /info "1"
    }
}

Also, the X-Dispatcher-Info header does not need a value, but if you use curl for testing, you must supply a value to send to the header, such as:

curl -v -H "X-Dispatcher-Info: true" https://localhost/content/wknd/us/en.html

Below is a list containing the response headers that X-Dispatcher-Info returns: