LVS and Varnish

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Wikimedia infrastructure

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LVS and Varnish infrastructure

Wikipedia request flow

Diagram of "text" traffic flow through Wikimedia front edge LVS/nginx/Varnish infrastructure.

Naming

  • eqiad is representative of whichever data centre is currently primary (codfw is similar).
  • esams is representative of all caching sites (ulsfo is similar).
  • "upload" traffic operates similarly to "text" shown here.

See Varnish and Clusters for more information about those in particular.

Routing

When LVS balances traffic to ports :80 (varnish), and :443 (nginx), it uses a hash of the client IP to help with TCP Fast Open and SSL session persistence respectively.

Within the caching layer (cp#xxx machines), the jump from nginx:443 to varnish:80 is direct on the local host.

However, the jump from varnish:80 (frontend) to varnish:3128 (backend) is different: for that jump, we hash on the URL (and other req meta-data) when balancing to the backends to divide the cache space among all machines, and thus the request typically moves from one machine to another within the same cluster.