Long description

Web servers and data servers are shown in the image. A browsing window is shown at the top left. Two arrows from this page labeled update "A" B C and retrieve "A" B C, points to the load balancer. Two arrows from the load balancer labeled retrieve "A" B C and update "A" B C, points to the first and fourth web servers among the four. Arrows from the first and fourth web servers, labeled retrieve "A" B C and Update "A" B C points to the two data servers. On the left it is labeled as follows: problem: how to ensure that this retrieval sees the updated version of "A" B C.