Difference between revisions of "MapGuide RFC 3 - Session Affinity"

Latest revision as of 20:55, 15 March 2007

This page has moved to the MapGuide Trac Wiki:

http://trac.osgeo.org/mapguide/wiki/MapGuideRfc3

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-===Overview===
+This page has moved to the MapGuide Trac Wiki:
-When multiple MapGuide instances are accessed via a load balancer, problems arise when a request that requires a session that was created on one MapGuide site server is processed by a different server. The proposed short-term solution to this problem is to ensure that any requests that make use of a session and its related resources are always processed by the same server that created (and therefore has access to) that session.
+http://trac.osgeo.org/mapguide/wiki/MapGuideRfc3
-===Motivation===
-In a deployment that uses multiple, synchronized MapGuide Servers, a load balancer will typically be used to distribute incoming client requests to a number of MapGuide Web Tier deployments. Each instance of the web tier makes use of a single MapGuide Site Server in order to process its requests.
-Many operations require the use of sessions in MapGuide. Once a session has been created, the server may create temporary resources in a session repository. A session repository is very similar to the main (Library://) repository, except that the resources it contains only persist for the lifetime of the session. Requests that require the use of such session-based resources can only succeed if they are present on the server. Thus, if the load balancer hits one web tier deployment, and hence one particular server when it creates a session, subsequent requests for that same session which get directed to an alternate web tier instance (and hence a different server) will fail. This is because the alternate server knows nothing about the requested session, and does not have a copy of the session repository.
-All requests related to that particular session will fail unless the load balancer happens to direct the request to the server that created it. Configuring a load balancer to determine the session and direct the request to a particular web tier instance would be complex and undesirable.
-The proposal is to modify MapGuide to handle the problem so that the load balancer configuration can be trivial.
-===Funding/Resources===
-Autodesk to supply the resources to make the required changes.
-===Proposed Changes===
-The proposed changes represent a short-term solution to this problem. In the long term, steps should be taken to ensure that any of the available servers in a site are capable of accessing sessions created on any of the other servers.
-The changes can be summarized as follows:
-) Modify the web tier so that it can be configured to access more than one site server - this allows each web tier instance to make use of all of the site servers.
-) Modify the web tier so that requests that require a session are always directed to the site server that created the session.
-) Modify the server code so that any support servers that require access to session resources are able to retrieve them from the appropriate site server.
-====Technical====
-To support item 1, the web tier needs to perform some rudimentary load-balancing to distribute requests among the available servers. A simple round-robin algorithm would suffice. Support for failover if errors occur or servers are taken offline is beyond the scope of this proposal.
-To support items 2 and 3, some means is required to map between a session ID and the corresponding server.
-===Implications===
-Client requests, particularly from the MapGuide viewers, often depend upon a session, so most of the traffic from a given client will always be directed back to the same server.
-===Test Plan===
-Testing will require multiple site servers, support servers, and web tiers to be deployed under a load balancer. Testing should then be carried out by making requests from multiple clients accessing different sessions.

Difference between revisions of "MapGuide RFC 3 - Session Affinity"

Latest revision as of 20:55, 15 March 2007

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