custom.backend.vcl-sample

# First backend definition, with a built-in probe
backend default {
    # I have Virtual Hosts that only listen to the Public IP
    # so no 127.0.0.1 for me
    # Backend is running on port 81
    .host = "127.0.0.1";
    .port = "80";
    .probe = {
        .url = "/ping";
        .timeout  = 1s;
        .interval = 10s;
        .window    = 5;
        .threshold = 2;
    }
    .first_byte_timeout     = 300s;   # How long to wait before we receive a first byte from our backend?
    .connect_timeout        = 5s;     # How long to wait for a backend connection?
    .between_bytes_timeout  = 2s;     # How long to wait between bytes received from our backend?
}

# Backend definition with entirely custom backend probes (raw HTTP headers) in a separated definition
backend custom_healthchecks {
    .host  = "127.0.0.1";
    .port  = "80";
    .probe = custom_backend_probe;    # Refer to the probe definition below, so we can reuse the probe.

    .first_byte_timeout     = 300s;
    .connect_timeout        = 5s;
    .between_bytes_timeout  = 2s;
}

probe custom_backend_probe {
  .request   = "GET /some/url HTTP/1.1"
               "Host: some.virtualhost.domain.Tld"
               "Connection: close"
               "Accept-Encoding: text/html"
               "User-Agent: Varnish Health Probe";
  .interval  = 10s;
  .timeout   = 10s;
  .window    = 2;
  .threshold = 2;
}

# Below is an example redirector based on the Client IP (same returning class C subnet IP will get
# rerouted to the same backend, as long as it's available).
#
# In order for these to work, you need to define 2 backends as shown above named 'web1' and 'web2' (replace 'default'
# from the example above).
director pool_clientip client {
  {
    .backend = web1;
    .weight = 1;
  }
  {
    .backend = web2;
    .weight = 1;
  }
}

# Below is an example that will round-robin (based on the weight) to each backend.
# Web2 will get twice the hits as web1 since it has double the weight (= preference).
director pool_clientip {
  {
    .backend = web1
    .weight = 1;
  }
  {
    .backend = web2
    .weight = 2;
  }
}