Self routing Varnish Cache cluster example using 302 redirects

self_route_302.vcl

# Self routing cluster example using 302 redirects
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? Did they come in with the right Host?
  # If yes, reroute to the backend
  # If not, redirect the request to the appropriate node
  if (req.http.X-shard == server.identity &&
      req.http.X-shard + ".example.com" == req.http.Host) {
    set req.backend_hint = content;
  } else {
    set req.http.X-redir = "https://" + req.http.X-shard +
      ".example.com" + req.url;
    return(synth(302, "Found"));
  }
  
  # Your VCL logic starts here
}

sub vcl_synth
{
  if (resp.status == 302) {
    set resp.http.Location = req.http.X-redir;
    return (deliver);
  }
}