Self routing Varnish Cache cluster example

self_route.vcl

# Self routing cluster example
vcl 4.0;

import directors;

backend node1 {
  .host = "node1.example.com";
  .port = "80";
}

backend node2 {
  .host = "node2.example.com";
  .port = "80";
}

backend node3 {
  .host = "node3.example.com";
  .port = "80";
}

backend content {
  .host = "content-origin.example.com";
  .port = "80";
}

sub vcl_init
{
  # We use a simple hash director to shard our content
  new cluster = directors.hash();
  cluster.add_backend(node1, 1);
  cluster.add_backend(node2, 1);
  cluster.add_backend(node3, 1);
}

sub vcl_recv
{
  # Figure out where the content is
  set req.backend_hint = cluster.backend(req.url);
  set req.http.X-shard = req.backend_hint;

  # Do we have the content? If yes, reroute to the backend
  # If not, pass the request to the appropriate node
  if (req.http.X-shard == server.identity) {
    set req.backend_hint = content;
  } else {
    return(pass);
  }
  
  # Your VCL logic starts here
}