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concept.md

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Concepts

  • Product:

    • The product equals "tenant" in BFE, which has its own configuration, such as routing policy, permission, etc.
    • Field "host" in HTTP header is used to identify product that the incoming message belongs to.
  • Cluster:

    • Cluster means a set of backend servers which provide same functionality and process similar task.
    • Usually,cluster span multiple IDC/region in scope。
  • Sub Cluster:

    • A cluster may be composed of multiple sub clusters conceptually。
    • Usally, backend servers within one IDC/region is defiend as a sub cluster.
  • Instance:

    • Instance is backend server. A sub cluster would contain multiple instances.
    • To BFE,each backend instance expose IP address + port to accept request.

Typical message routing flow

Traffic Forwarding

  • Step1-2:DNS query

    • request host name:demo.example.com
    • get IP address 6.6.6.6(example)
  • Step3:IP diagram is routed to POP of IDC1,and processed by layer 4 load balancer L4LB.

  • Step4:L4LB forward diagram to BFE

  • Step5:BFE receive HTTP request, identify which product the request belongs to:

    • BFE uses field "host" in HTTP header to decide product.
    • In this scenario, assume demo.example.com belongs to product "demo".
  • Step6:Identify a cluster of product "demo", which would handle this message.

    • Based on configured distribution rule of product "demo", identify cluster "demo-static" in this product to handle the message .
  • Step7:Identify a sub cluster within "demo-static"

    • Based on routing rule in "demo-static", identify sub cluster "demo-static.idc1" to handle this message.
  • Step8:Identify instance

    • based on configured load balancing policy, identify instance as "a-demo-static-1.idc1".
  • Step9:request is sent to instance "a-demo-static-1.idc1".

  • Step10:BFE receive response message from "a-demo-static-1.idc1".

  • Step11-12:BFE send back response to client, via L4LB.