Shulou(Shulou.com)06/02 Report--

When a traditional Web project needs to expand from a single point to a cluster, there is a problem to consider: the implementation of distributed Session. There are usually three solutions for distributed session. Now we simply record these three ways:

1.session broadcast

As the name implies, broadcasting is that all the servers in the cluster synchronize their session to other servers, so that each server has the session information of other servers, so that no matter which server the request enters, the session information can be obtained. This method is relatively simple in understanding and implementation, and avoids the problem of session loss caused by a single point of failure. However, because broadcasting is a process in which multiple servers are synchronized, there will be a certain delay, so it is only suitable for the case of small cluster size and low network overhead.

two。 Viscous session

This is a way to specify session, which distributes all requests to the specified server at the routing of the cluster, so that a request with session goes to the same back-end server every time. This method has no additional network overhead and is suitable for medium-sized clusters, but because each request corresponds to a server, when there is a server down machine, the corresponding session will be lost, resulting in a single point of failure.

3. Centralized cache management

The session information is taken out separately, and all the session information is placed in the specified cache for centralized management. All requests with session will be processed here first, and then distributed to the backend server accordingly. Commonly used caches are memcache, redis, and so on. This method is used in large clusters to facilitate the increase of cluster nodes, but the stability depends on the stability of the cache, so it is necessary to have a reasonable write strategy to avoid the loss of session after cache failure.

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