Summary of this picture: We have requests coming in from clients. The load balancer assigns these requests to different workers in the system in a way that should ensure evenness of work distribution among all its active workers. Meanwhile, the performance monitor checks to see that the system is still performing within an acceptable throughput range. If so, nothing changes; if not, it might tell the system to boot up more workers.
The servers themselves handle the requests as necessary, in some cases reading files from disk, performing computations on the inputs, or making a call to the database. When making calls to the database, they first make requests to the memcached servers to check if the desired database query has already been performed. If so, they retrieve that value directly; otherwise they make the database call and then later store the result in the cache.
The database is often replicated, as in the picture, to contain a master database with all the write updates, as well as "slaves", copies of the master which can be easily read from. This enables more efficient access to the database, since the load on the database is spread out instead of being directed to a single master.
Summary of this picture: We have requests coming in from clients. The load balancer assigns these requests to different workers in the system in a way that should ensure evenness of work distribution among all its active workers. Meanwhile, the performance monitor checks to see that the system is still performing within an acceptable throughput range. If so, nothing changes; if not, it might tell the system to boot up more workers.
The servers themselves handle the requests as necessary, in some cases reading files from disk, performing computations on the inputs, or making a call to the database. When making calls to the database, they first make requests to the memcached servers to check if the desired database query has already been performed. If so, they retrieve that value directly; otherwise they make the database call and then later store the result in the cache.
The database is often replicated, as in the picture, to contain a master database with all the write updates, as well as "slaves", copies of the master which can be easily read from. This enables more efficient access to the database, since the load on the database is spread out instead of being directed to a single master.
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