Max connections


I’m confused about Max Connections in the docs:

503 Backend.max_conn Reached
Each backend in your Fastly service has an associated maximum number of connections. Varnish will respond with this error when it makes a request to a backend that has reached the defined limit. By default we limit you to 200 origin connections from a single cache node to protect origins from overload. If you want to change the number of connections, access the Hosts area of the configurations settings and select Advanced Configuration settings on an origin or backend object (via the gear icon next to the name) then, modify the Max Connection field to a higher number.

Does this mean by default, the Fastly will only allow 200 connections to the backend (e.g. misses) or 200 connections or requests to the backend total?





The 200 connections to your origin is per cache node . And this is connections, not requests…we will hold backend connections open and pipe multiple requests across the open connection. This error tends to be when the backend origin server has hit a connection limit from us. You can increase the number of connections we make per cache node to your origins if the limit really is on the Fastly layer.